电子束和激光的差异研究

No abstract

No abstract

Electron beam melting (EBM) and selective laser melting (SLM) are two advanced rapid prototyping manufacturing technologies capable of fabricating complex structures and geometric shapes from metallic materials using computer tomography (CT) and Computer-aided Design (CAD) data. Compared to traditional technologies used for metallic products, EBM and SLM alter the mechanical, physical and chemical properties, which are closely related to the biocompatibility of metallic products. In this study, we evaluate and compare the biocompatibility, including cytocompatibility, haemocompatibility, skin irritation and skin sensitivity of Ti6Al4V fabricated by EBM and SLM. The results were analysed using one-way ANOVA and Tukey's multiple comparison test. Both the EBM and SLM Ti6Al4V exhibited good cytobiocompatibility. The haemolytic ratios of the SLM and EBM were 2.24% and 2.46%, respectively, which demonstrated good haemocompatibility. The EBM and SLM Ti6Al4V samples showed no dermal irritation when exposed to rabbits. In a delayed hypersensitivity test, no skin allergic reaction from the EBM or the SLM Ti6Al4V was observed in guinea pigs. Based on these results, Ti6Al4V fabricated by EBM and SLM were good cytobiocompatible, haemocompatible, non-irritant and non-sensitizing materials. Although the data for cell adhesion, proliferation, ALP activity and the haemolytic ratio was higher for the SLM group, there were no significant differences between the different manufacturing methods.

Additive manufacture (AM) appears to be the most suitable technology to produce sophisticated, high quality, lightweight parts from Ti6Al4V alloy. However, the fatigue life of AM parts is of concern. In our study, we focused on a comparison of two techniques of additive manufacture-selective laser melting (SLM) and electron beam melting (EBM)-in terms of the mechanical properties during both static and dynamic loading. All of the samples were untreated to focus on the influence of surface condition inherent to SLM and EBM. The EBM samples were studied in the as-built state, while SLM was followed by heat treatment. The resulting similarity of microstructures led to comparable mechanical properties in tension, but, due to differences in surface roughness and specific internal defects, the fatigue strength of the EBM samples reached only half the value of the SLM samples. Higher surface roughness that is inherent to EBM contributed to multiple initiations of fatigue cracks, while only one crack initiated on the SLM surface. Also, facets that were formed by an intergranular cleavage fracture were observed in the EBM samples.

No abstract

The use of additive manufacturing technologies to produce lightweight or functional structures is widespread. Especially Ti6Al4V plays an important role in this development field and parts are manufactured and analyzed with the aim to characterize the mechanical properties of open-porous structures and to generate scaffolds with properties specific to their intended application. An SLM and an EBM process were used respectively to fabricate the Ti6Al4V single struts. For mechanical characterization, uniaxial compression tests and hardness measurements were conducted. Furthermore, the struts were manufactured in different orientations for the determination of the mechanical properties. Roughness measurements and a microscopic characterization of the struts were also carried out. Some parts were characterized following heat treatment (hot isostatic pressing). A functional correlation was found between the compressive strength and the slenderness ratio (λ) as well as the equivalent diameter (d) and the height (L) of EBM and SLM parts. Hardness investigations revealed considerable differences related to the microstructure. An influence of heat treatment as well as of orientation could be determined. In this work, we demonstrate the influence of the fabrication quality of single struts, the roughness and the microstructure on mechanical properties as a function of orientation.

This article gives a comparison between laser beam welding and electron beam welding. In a first step, the basic principles and properties of both methods and/or the resulting weld joints are specified, afterwards the research results from laser beam welding in vacuum are presented. Thanks to modern laser systems (fibre laser and/or disk laser) and their excellent beam quality, laser beam welding in vacuum allows a direct comparison of the process behaviour, the development of the keyhole and the respective welding results from both beam welding methods. The welding possibilities of this process variation are demonstrated, the advantages with regard to electron beam welding and/or the disadvantages compared to laser beam welding in atmosphere are discussed and the need for future research are specified.

No abstract

No abstract

Welding characteristics of Ti-5Al-5V-5Mo-3Cr (Ti5553) alloy has been investigated. The weld joints were performed by laser beam (LBW), electron beam (EBW) and gas tungsten arc welding (GTAW). Regardless of the welding method used, the welds showed low hardness values with coarse columnar grains in the fusion zone (FZ) and retained equiaxed beta phase within the heat affected zone (HAZ). Larger grains were present at the near HAZ compared with far HAZ (near base metal). The strengths of the welded samples were lower than the base metal. Fracture occurred at the weld zones with transgranular and microvoid coalescence fracture mechanism.

No abstract

Abstract Surface degradation of linen fabric induced by laser treatment with the aim of reproducing an image was investigated and compared with the degradation induced by an electron beam and a heat source. The results confirm that the brown shades obtained by the laser beam are mainly due to surface tar formation, and that the degradation pattern is similar to that observed by treatment with an electron beam. Surface thermal treatment, however, showed different fibre behaviour.

Depending on the application, establishing a strategy for selecting the type of powder bed fusion technology—from electron beam (EB-PBF) or laser powder bed fusion (L-PBF)—is important. In this study, we focused on the β-type Ti–15Mo–5Zr–3Al alloy (expected for hard-tissue implant applications) as a model material, and we examined the variations in the microstructure, crystallographic texture, and resultant mechanical properties of specimens fabricated by L-PBF and EB-PBF. Because the melting mode transforms from the conduction mode to the keyhole mode with an increase in the energy density in L-PBF, the relative density of the L-PBF-built specimen decreases at higher energy densities, unlike that of the EB-PBF-built specimen. Although both EB-PBF and L-PBF can obtain cubic crystallographic textures via bidirectional scanning with a 90° rotation in each layer, the formation mechanisms of the textures were found to be different. The <100> texture in the build direction is mainly derived from the vertically grown columnar cells in EB-PBF, whereas it is derived from the vertically and horizontally grown columnar cells in L-PBF. Consequently, different textures were developed via bidirectional scanning without rotation in each layer: the <110> and <100> aligned textures along the build direction in L-PBF and EB-PBF, respectively. The L-PBF-built specimen exhibited considerably better ductility, but slightly lower strength than the EB-PBF-built specimen, under the conditions of the same crystallographic texture and relative density. We attributed this to the variation in the microstructures of the specimens; the formation of the α-phase was completely absent in the L-PBF-built specimen. The results demonstrate the importance of properly selecting the two technologies according to the material and its application.

No abstract

No abstract

No abstract

No abstract

No abstract

No abstract

Abstract This research compared high‐cycle fatigue (HCF) performances of joints of Ti–6Al–4V titanium (TC4) alloy with the thickness of 30 mm welded by vacuum electron beam welding (EBW) and laser welding with filler wire (LWFW) (hereinafter referred to as EBW and LWFW joints). Under test conditions, the fatigue strength of the LWFW joint is only 65% that of the EBW joint. Based on analysis, the main reason is that a larger microhardness gradient is present in the LWFW joint. The average microhardness of the weld metal (WM) of the LWFW joint is 41 HV lower than that of base metal (BM). A lot of punctate β phases in the WM of the LWFW joint may be an important reason for its softening. The research results provide data supports for the application of the EBW and LWFW of Ti alloy in the field of aviation manufacturing.

No abstract

No abstract

In this study, samples of alloy Ti-6Al-4V have been processed by different additive manufacturing techniques in order to compare the resulting microstructure. In all three processes, ultrafast cooling gives rise to strongly out-of-equilibrium microstructures. However, the specific of the heat flow in each process lead to significant differences as far as the grains orientation and the resulting microstructural anisotropy are concerned.

Laser or electron beams are used as tools for welding, cutting, drilling melting, tempering or vaporizing in many machining tasks. These beams have fundamentally different physical natures. They are produced differently, and behave fundamentally differently when penetrating material. The differences between electron and laser devices that occur in machining, the advantages and disadvantages of these technologies in comparison with one another, will be discussed in this article. Using a more detailed description of electron beam technology, comparisons between laser and electron beam technology will be discussed.

Abstract Powder-bed fusion (PBF) process is a subdivision of additive manufacturing (AM) technology where a heat source at a controlled speed selectively fuses regions of a powder-bed material to form three-dimensional (3D) parts in a layer-by-layer fashion. Two of the most commercialized and powerful PBF methods for fabricating full-density metallic parts are the laser PBF (L-PBF) and electron beam PBF (E-PBF) processes. In this study, a multiphysics-based 3D numerical model is developed to compare the thermo-fluid properties of Ti-6Al-4V melt pools formed by the L-PBF and E-PBF processes. The temperature-dependent properties of Ti-6Al-4V alloy and the parameters for the laser and electron beams are incorporated in the model as the user-defined functions (UDFs). The melt-pool geometry and its thermo-fluid behavior are investigated using the finite volume (FV) method, and results for the variations of temperature, thermo-physical properties, velocity, geometry of the melt pool, and cooling rate in the two processes are compared under similar irradiation conditions. For an irradiance level of 26 J/mm3 and a beam interaction time of 1.212 ms, simulation results show that the L-PBF process gives a faster cooling rate (1. 5 K/μs) than that in the E-PBF process (0.74 K/μs). The magnitude of liquid velocity in the melt pool is also higher in L-PBF than that in E-PBF. The numerical model is validated by comparing the simulation results for the melt-pool geometry with the PBF experimental results and comparing the numerical melt-front position with the analytical solution for the classical Stephan problem of melting of a phase-change material (PCM).

Abstract Reduced pressure laser welds were made using a 6-kW commercial fiber-laser system on Ti-6Al-4 V and compared to electron beam welds of the same beam diameters as measured by beam diagnostics. The laser welds showed keyhole characteristics under easily achievable mechanical pumped vacuum levels of 1 mbar pressure that nearly matched the electron beam weld penetrations made at 9 × 10 –5 mbar vacuum. Ti-6Al-4 V alloys were used to represent refractory metals such as vanadium, tantalum, zirconium, or molybdenum that require vacuum or highly protective inert gas protection systems to prevent adverse interactions with air and can be difficult to weld under non-vacuum conditions. Results show that laser weld depths of 20 mm with aspect ratios of 17:1 can be made under what appears to be stable keyhole behavior as the result of reduced pressure. The effect of fiber diameter was examined using 0.1-, 0.2-, and 0.3-mm fibers, showing that small spot sizes can easily be achieved at long focal length lenses of 400 and 500 mm. The 0.1- and 0.2-mm fibers produced keyhole welds with minimal amounts of porosity, which was only present at 2 kW or higher, while the 0.3-mm fiber produced keyhole welds with more rounded roots that were porosity free as shown by radiography up to the maximum power of 6 kW. Correlations between weld depth and processing conditions are presented for the reduced pressure laser. These results are directly compared to electron beam welds, facilitating design of future reduced pressure laser systems targeted for deep weld penetrations historically developed for electron beams.

A comparative study on fatigue crack growth behaviour was made between the electron-beam powder-bed-fusion (PBF-EB) and laser powder-bed-fusion (PBF-LB) Inconel 718. The crack followed a transgranular path with a faster propagation rate for the PBF-EB Inconel 718, whereas a combination of intergranular and transgranular path was observed for the PBF-LB, and its slower rate being comparable to the wrought counterpart. The main fatigue crack in the PBF-EB Inconel 718 exhibited a sawtooth shaped path at the micro-scale, with intensive slip traces close to the crack surfaces owing to the very low work hardening rate. Based on the digital image correlation (DIC) analysis of the crack tip field, fatigue-crack sawtooth path in the PBF-EB Inconel 718 can be successfully predicted by using a strain energy density criterion, which dictates the crack growth follows the direction of minimum distance from the crack tip to elasto-plastic boundary. For the PBF-LB Inconel 718, the predominant fatigue crack was straight at low ΔK, but severe deflections occurred at the medium and high ΔK regimes. A clear correlation exists between the incipient intergranular cracks and the main crack path deflection. This suggests that once the accumulated damage in the plastic zone around the crack tip reaches the critical value, intergranular cracks can form the new front of the fatigue crack, causing the main crack path deflection. Elasto-plastic fracture mechanics parameters of rp and ΔCTOD, derived from the DIC-based crack tip field analysis, can qualitatively predict the lower crack growth rate of the PBF-LB Inconel 718.

Ti-6Al-4V alloy fabricated by laser powder bed fusion (L-PBF) and electron beam powder bed fusion (EB-PBF) techniques have been studied for applications ranging from medicine to aviation. The fabrication technique is often selected based on the part size and fabrication speed, while less attention is paid to the differences in the physicochemical properties. Especially, the relationship between the evolution of α, α’, and β phases in as-grown parts and the fabrication techniques is unclear. This work systematically and quantitatively investigates how L-PBF and EB-PBF and their process parameters affect the phase evolution of Ti-6Al-4V and residual stresses in the final parts. This is the first report demonstrating the correlations among measured parameters, indicating the lattice strain reduces, and c/a increases, shifting from an α’ to α+β or α structure as the crystallite size of the α or α’ phase increases. The experimental results combined with heat-transfer simulation indicate the cooling rate near the β transus temperature dictates the resulting phase characteristics, whereas the residual stress depends on the cooling rate immediately below the solidification temperature. This study provides new insights into the previously unknown differences in the α, α’, and β phase evolution between L-PBF and EB-PBF and their process parameters.

In the following paper we present the investigation of microstructure and mechanical properties produced by selective laser melting (SLM) and electron beam melting (EBM). The chosen alloy is a Ti-(46- 48)Al-2Cr-2Nb alloy which has a great potential in replacing heavy weight Ni-base superalloys in turbine blades. Cylindrical specimens were produced and characterized by optical microscopy (OM), scanning electron microscopy (SEM) and chemical analysis to determine the microstructure and composition. In addition compression tests at room and elevated temperatures (700-800 °C) were carried out to identify the mechanical properties of the alloy.

The current paper is to compare the welding characteristics as well as the post-weld impact and bending properties of electron-beam welded (EBW) and laser-beam-welded (LBW) 5 mm thick AA 8090 Al–Li alloy plates. In comparison under the same weld depth of 5 mm, the as-welded or T6 EBW specimens exhibited higher strength and fracture toughness than the LBW counterparts by ∼7% or ∼24%, respectively. The grain size and δ′ precipitate size in the EBW specimens were smaller than those in the LBW ones due to mainly the lower heat input absorbed. The uniformly dispersed pores in the EBW specimens originating from volatile element evaporation were spherical in shape, <0.2 mm in size, and ∼1.3% in volume fraction, compared with the spherical or elongated pores in the LBW ones of 0.05–1 mm in size and ∼7.2% in volume fraction originating primarily from the bubbles ejected into the molten pool due to intense evaporation at the bottom part of a keyhole with the entrapment of shielding gas during rapid solidification. The joint efficiency in terms of strength was typically around 80%, which might be considered to be acceptable. But if the welded specimens were loaded under high-rate impact with a V-notch and hence multiaxial stresses, both the EBW and LBW specimens would be subject to unacceptably low joint efficiency in terms of fracture absorbed energy Et (below 20%). The Et joint efficiency decreased with increasing loading rate.

Powder bed fusion processes based additively manufactured SS 316L components fall short of surface integrity requirements needed for optimal functional performance. Hence, machining is required to achieve dimensional accuracy and to enhance surface integrity characteristics. This research is focused on comparing the material removal performance of 316L produced by PBF-LB (laser) and PBF-EB (electron beam) in terms of tool wear and surface integrity. The results showed comparable surface topography and residual stress profiles. While the hardness profiles revealed work hardening at the surface where PBF-LB specimens being more susceptible to work hardening. The investigation also revealed differences in the progress of the tool wear when machining specimens produced with either PBF-LB or PBF-EB.

Electron beam (EBAM) and laser beam (LBAM) additive manufacturing processes with a deposited material in the form of a wire are an efficient methods enabling the making of component parts. The scope of the presented work was to investigate the influence of technological process on microstructure and mechanical properties such as tensile strength, microhardness and elongation of the fabricated components. The achieved results and gained knowledge will enable the production of a whole structure from stainless steel in the future. The metallographic examination revealed that the microstructure is not fully homogenies, the cell-dendritic areas occurred. Moreover, the microhardness profiles indicated that some fluctuation in the microstructure as well as mechanical properties can be observed on the cross section of deposited components. However, the mechanical tests showed that the tensile strength as well as elongation fulfil the requirement of producer of deposited wire.

No abstract

No abstract

No abstract

No abstract

Additive manufacturing (AM) of metals is expanding and already starts to reach industrial scale. Among many different technologies of AM, powder-bed technologies are the most widespread as they provide the highest resolution and so the widest options in the production of complex parts. Selective laser melting (SLM) and electron beam melting (EBM) both belong to this technological group. In this paper, we describe the differences between these two technologies on the example of titanium alloy production. Due to different material states in the as-built condition, the material shows a different response to heat treatment. We depict the differences by microstructure observations and hardness measurement after annealing the titanium alloy at temperatures of 100-1000 °C and subsequent water quenching. While the titanium alloy is stable when manufactured by EBM, it shows microstructural changes associated with changes in mechanical properties when manufactured by SLM.

This article reviews published data on the mechanical properties of additively manufactured metallic materials. The additive manufacturing techniques utilized to generate samples covered in this review include powder bed fusion (e.g., EBM, SLM, DMLS) and ...Read More

The most popular additive manufacturing (AM) technologies to produce titanium alloy parts are electron beam melting (EBM), selective laser melting (SLM) and directed energy deposition (DED). This investigation explores mainly these three techniques and compares these three methods comprehensively in terms of microstructure, tensile properties, porosity, surface roughness and residual stress based on the information available in the literature. It was found that the microstructure is affected by the highest temperature generated and the cooling rate which can be tailored by the input variables of the AM processes. The parts produced from EBM have strength comparable to that of conventionally fabricated counterparts. SLM and DED yield superior strength, which can be up to 25% higher than traditionally manufactured products. Due to the presence of larger tensile residual stress, surface roughness and porosity, AM fabricated parts have lower fatigue life compared to those of from traditional methods. EBM parts have slightly lower fracture toughness (i.e., lower fatigue life) than conventionally produced parts while SLM and DED have significantly lower fracture toughness. Annealing, hot isostatic pressing, stress relief and additional machining processes improve the characteristics of parts produced from AM. Ti–6Al–4V alloy parts fabricated via AM may have limited applications despite the high demands in aerospace or biomedical engineering. Since rapid product development using 3D printers leads to significant cost reductions more recently, it is expected that more opportunities may soon be available for the AM of titanium alloys with newer AM processes such as cold spray additive manufacturing (CSAM) and additive friction stir deposition (AFSD).

No abstract

This article reviews published data on the mechanical properties of additively manufactured metallic materials. The additive manufacturing techniques utilized to generate samples covered in this review include powder bed fusion (e.g., EBM, SLM, DMLS) and ...Read More

Electron beam melting (EBM), as one of metal additive manufacturing technologies, is considered to be an innovative industrial production technology. Based on the layer‐wise manufacturing technique, as‐produced parts can be fabricated on a powder bed using the 3D computational design method. Because the melting process takes place in a vacuum environment, EBM technology can produce parts with higher densities compared to selective laser melting (SLM), particularly when titanium alloy is used. The ability to produce higher quality parts using EBM technology is making EBM more competitive. After briefly introducing the EBM process and the processing factors involved, this paper reviews recent progress in the processing, microstructure, and properties of titanium alloys and their composites manufactured by EBM. The paper describes significant positive progress in EBM of all types of titanium in terms of solid bulk and porous structures including Ti–6Al–4V and Ti–24Nb–4Zr–8Sn, with a focus on manufacturing using EBM and the resultant unique microstructure and service properties (mechanical properties, fatigue behaviors, and corrosion resistance properties) of EBM‐produced titanium alloys.

This paper provides a brief review of relatively new additive manufacturing technologies for the fabrication of unusual and complex metal and alloy products by laser and electron beam melting. A number of process features and product microstructures are illustrated utilizing 3D optical and transmission electron microscope image compositions representing examples of 3D materials science. Processing methods involving electron beam melting (EBM) and a process referred to as direct metal laser sintering (DMLS), often called selective laser melting (SLM) are described along with the use of light (optical) microscopy (OM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) to elucidate microstructural phenomena. Examples of EBM and SLM studies are presented in 3D image compositions. These include EBM of Ti-6Al-4V, Cu, Co-base superalloy and Inconel 625; and SLM of 17-4 PH stainless steel, Inconel 718 and Inconel 625. 3D image compositions constituting 3D materials science provide effective visualization for directional solidification-related phenomena associated with the EBM and SLM fabrication of a range of metals and alloys, especially microstructures and microstructural architectures.

This article reviews published data on the mechanical properties of additively manufactured metallic materials. The additive manufacturing techniques utilized to generate samples covered in this review include powder bed fusion (e.g., EBM, SLM, DMLS) and ...Read More

This article reviews published data on the mechanical properties of additively manufactured metallic materials. The additive manufacturing techniques utilized to generate samples covered in this review include powder bed fusion (e.g., EBM, SLM, DMLS) and ...Read More

Additive Manufacturing (AM) methods are generally used to produce an early sample or near net-shape elements based on three-dimensional geometrical modules. To date, publications on AM of metal implants have mainly focused on knee and hip replacements or bone scaffolds for tissue engineering. The direct fabrication of metallic implants can be achieved by methods, such as Selective Laser Melting (SLM) or Electron Beam Melting (EBM). This work compares the SLM and EBM methods used in the fabrication of titanium bone implants by analyzing the microstructure, mechanical properties and cytotoxicity. The SLM process was conducted in an environmental chamber using 0.4–0.6 vol % of oxygen to enhance the mechanical properties of a Ti-6Al-4V alloy. SLM processed material had high anisotropy of mechanical properties and superior UTS (1246–1421 MPa) when compared to the EBM (972–976 MPa) and the wrought material (933–942 MPa). The microstructure and phase composition depended on the used fabrication method. The AM methods caused the formation of long epitaxial grains of the prior β phase. The equilibrium phases (α + β) and non-equilibrium α’ martensite was obtained after EBM and SLM, respectively. Although it was found that the heat transfer that occurs during the layer by layer generation of the component caused aluminum content deviations, neither methods generated any cytotoxic effects. Furthermore, in contrast to SLM, the EBM fabricated material met the ASTMF136 standard for surgical implant applications.

Additive manufacturing (AM) is recognized as a core technology for producing high value, complex, and individually designed components as well as prototypes, giving AM a significant advantage over subtractive machining. Selective laser melting (SLM) or electron beam melting (EBM) are two of the main technologies used for producing metal components. The powder size varies, depending on the technology and manufacturer, from 20–50 μm for SLM and 45–100 μm for EBM. One of the current barriers for implementing AM for most industries is the lack of build repeatability and a deficit in quality assurance standards. The mechanical properties of the components depend critically on the density achieved; therefore, defect analysis and detection of unfused powder must be carried out to verify the integrity of the components. Detecting unfused powder in AM parts using X-ray computed tomography (XCT) is challenging because detection relies on variations in density. Unfused particles have the same density as the manufactured parts; therefore, detection is difficult using standard methods for density measurement. This study presents a methodology to detect unfused powders in SLM and EBM-manufactured components. Aluminum and titanium artefacts with designed internal defects filled with unfused powder are scanned with XCT and the results are analyzed with VGSTUDIO Max 3.0 (Volume Graphics, Germany) software package. Preliminary results indicate that detecting unfused powder in an aluminum SLM artifact with a 9.5 μm voxel size is achievable. This is possible because of the size of the voids between the powder particles and the non-uniform shape of the particles. Conversely, detecting unfused powder in the EBM-manufactured titanium artifact is less challenging owing to the uniform spherical shape and slightly larger size of the particles.

This article reviews published data on the mechanical properties of additively manufactured metallic materials. The additive manufacturing techniques utilized to generate samples covered in this review include powder bed fusion (e.g., EBM, SLM, DMLS) and ...Read More

No abstract

The surface texture of additively manufactured metallic surfaces made by powder bed methods is affected by a number of factors, including the powder's particle size distribution, the effect of the heat source, the thickness of the printed layers, the angle of the surface relative to the horizontal build bed and the effect of any post processing/finishing. The aim of the research reported here is to understand the way these surfaces should be measured in order to characterise them. In published research to date, the surface texture is generally reported as an Ra value, measured across the lay. The appropriateness of this method for such surfaces is investigated here. A preliminary investigation was carried out on two additive manufacturing processes—selective laser melting (SLM) and electron beam melting (EBM)—focusing on the effect of build angle and post processing. The surfaces were measured using both tactile and optical methods and a range of profile and areal parameters were reported. Test coupons were manufactured at four angles relative to the horizontal plane of the powder bed using both SLM and EBM. The effect of lay—caused by the layered nature of the manufacturing process—was investigated, as was the required sample area for optical measurements. The surfaces were also measured before and after grit blasting.

Metal powder Additive Manufacturing (AM) allows complex parts to be build from commercial materials. Several industries such as automotive, aerospace and medical have interests in using these technologies. However in metal powder AM, supports/ anchors are required to be melted in place to avoid process failure due to upward warping of flat overhanging geometries. This leads to additional melting of materials, processing time and thus increasing costs of parts build. A series of experiments were conducted to understand capability of processes such as Selective Laser Melting (SLM) and Electron Beam Melting (EBM) to build flat overhang geometries. In addition, effect of preheating the powder feedstock was also performed.

Nickel-based superalloys processed by additive manufacturing have demonstrated directional solidification, which has been shown to equal or improve mechanical properties compared to cast and wrought alloys. Inconel 625 cylinders have been manufactured by electron beam melting (EBM) and selective laser melting (SLM) and compared. EBM cylinders were built in the Z-axis direction (parallel to the build direction), and SLM cylinders were built in XY-axis (perpendicular to build direction) and Z-axis directions. The microstructures of as-fabricated as well as fabricated and HIPed cylinders were characterized by light optical metallography (LOM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive (X-ray) spectroscopy (EDS). EBM fabricated components contained columnar plates of ?¢¢ (Ni3Nb) precipitates while SLM components contained columnar arrays of fine ?¢¢ nanoparticles. The EBM fabricated and HIPed samples and SLM fabricated and HIPed samples exhibited equiaxed grains, but both components contained complex arrays of dissimilar precipitates.

No abstract

The continued drive for increased efficiency, performance and reduced costs for industrial gas turbine engines demands extended use of high strength-high temperature capability materials, such as nickel based superalloys. To satisfy the requirements of the component design and manufacturing engineers, these materials must be capable of being welded in a satisfactory manner. The present paper describes the characteristic defects found as a result of welding the more difficult, highly alloyed materials and reviews a number of welding processes used in the manufacture and repair of nickel alloy components. These include gas tungsten arc (GTA) and electron beam (EB) welding, laser powder deposition and friction welding. Many of the more dilute nickel based alloys are readily weldable using conventional GTA processes; however, high strength, precipitation hardened materials are prone to heat affected zone and strain age cracking defect formation. A number of factors are found to affect the propensity for defects: composition (aluminium and titanium content), grain size, pre- and post-weld heat treatment, as well as the welding process itself (control of heat input and traverse speed). Process parameter identification is still largely empirical and a fuller understanding of the joining processes is dependent upon the development and application of more sophisticated numerical modelling techniques.

A unique experiment carried out at TWI a few years ago compared the welding performance of a number of fibre-delivered lasers with beam qualities ranging between 4 and 23mm.mrad, under identical processing conditions, and demonstrated the effect of laser beam brightness, together with beam quality and spot diameter, on the welding performance on both steel and aluminium. This paper describes a continuation of this earlier study, carrying out welding under identical processing conditions and comparing, against these initial results, the welding performances of laser beams with even higher beam qualities (higher brightness) and of an in-vacuum electron beam. This investigation demonstrates that the welding performance of a high-brightness laser set-up is highly dependent on the conditions of the metal vapour column forming between the processing point and the focusing lens. The effective removal of this metal vapour column, which scatters and/or absorbs some of the incident laser power, is essential in maximising the welding performance that is achievable with high-brightness lasers. By using an argon side-jet shielding and a series of argon cross-jets along the beam path between the focusing lens and the processing point, it was shown that the welding performance of high-brightness lasers could be improved considerably, and matching, or possibly surpassing, that of an equivalent beam quality in-vacuum electron beam used under similar conditions of power, spot size and welding speed.

No abstract

Titanium alloys used in aerospace structures require joints of high integrity to meet the design requirements. Gas tungsten arc welding (GTAW), laser beam welding (LBW) and electron beam welding (EBW) are all processes capable of creating fusion welded joints. Gas tungsten arc welding offers the potential to achieve welds of equal quality to EBW or LBW at much lower capital costs; however, the application of GTAW involves gaining an understanding of the complex process characteristics. This paper reviews the process characteristics for GTAW titanium alloys and compares these characteristics with EBW and LBW titanium alloys. The characteristics of active flux tungsten inert gas welding and keyhole mode GTAW, two recent developments to GTAW, are considered, as is keyhole mode plasma arc welding. These variants are capable of greater penetration and, in some cases, faster processing speeds than conventional GTAW. Finally, the current knowledge of weld microstructural development in cast and wrought α + β titanium alloys and the mechanical performance of such welded joints are examined. Notably, conduction mode GTAWs are shown to have comparable mechanical properties with EBWs in relation to both cast and wrought base metals.

No abstract

No abstract

Current additive manufacturing (AM) processes are mainly focused on powder bed technologies, such as electron beam melting (EBM) and selective laser melting (SLM). However, the main disadvantages of such techniques are related to the high cost of metal powder, the degree of energy consumption, and the sizes of the components, that are limited by the size of the printing cell. The aim of the present study was to evaluate the environmental behavior of low carbon steel (ER70S-6) produced by a relatively inexpensive AM process using wire feed arc welding. The mechanical properties were examined by tension testing and hardness measurements, while microstructure was assessed by scanning electron microscopy and X-ray diffraction analysis. General corrosion performance was evaluated by salt spray testing, immersion testing, potentiodynamic polarization analysis, and electrochemical impedance spectroscopy. Stress corrosion performance was characterized in terms of slow strain rate testing (SSRT). All corrosion tests were carried out in 3.5% NaCl solution at room temperature. The results indicated that the general corrosion resistance of wire arc additive manufacturing (WAAM) samples were quite similar to those of the counterpart ST-37 steel and the stress corrosion resistance of both alloys was adequate. Altogether, it was clearly evident that the WAAM process did not encounter any deterioration in corrosion performance compared to its conventional wrought alloy counterpart.

No abstract

Owing to its potential application prospect in novel accident tolerant fuel, molybdenum alloys and their welding technologies have gained great importance in recent years. The challenges of welding molybdenum alloys come from two aspects: one is related to its powder metallurgy manufacturing process, and the other is its inherent characteristics of refractory metal. The welding of powder metallurgy materials has been associated with issues such as porosity, contamination, and inclusions, at levels which tend to degrade the service performances of a welded joint. Refractory metals usually present poor weldability due to embrittlement of the fusion zone as a result of impurities segregation and the grain coarsening in the heat-affected zone. A critical review of the current state of the art of welding Mo alloys components is presented. The advantages and disadvantages of the various methods, i.e., electron-beam welding (EBW), tungsten-arc inert gas (TIG) welding, laser welding (LW), electric resistance welding (ERW), and brazing and friction welding (FW) in joining Mo and Mo alloys, are discussed with a view to imagine future directions. This review suggests that more attention should be paid to high energy density laser welding and the mechanism and technology of welding Mo alloys under hyperbaric environment.

Welding and joining of magnesium alloys exert a profound effect on magnesium application expansion, especially in ground and air transportations where large-size, complex components are required. This applies to joi n t s b e t w e e n d i f f e r e n t g r a d e s o f c a s t a n d wrought magnesium alloys and to dissimilar joints with other materials, most frequently with aluminum and steel. Due to specific physical properties of magnesium, its welding requires low and well controlled power input. Moreover, very high affinity of magnesium alloys to oxygen requires shielding gases which protect the liquid weld from an environment. To magnify complexity, also solid state reaction with oxygen, which forms a thermodynamically stable natural oxide layer on magnesium surface, is an inherent deficiency of joining Both the conventional and novel welding techniques were adapted to satisfy these requirements, including arc welding, resistance spot welding, electromagnetic welding, friction stir welding, electron beam and laser welding. Since fusion welding has a tendency to generate porosities and part distortion, many alternative joining practices were implemented. These include soldering, brazing, adhesive bonding and mechanical fastening. However, also the latter techniques have disadvantages associated, for example, with stress induced by drilling holes during mechanical fastening, preheating during clinching or extensive surface preparation in adhesive bonding. Hence, experiments are in progress with completely novel ideas of magnesium joining. An application of magnesium is often in multi-material structures, requiring dissimilar joints, involving magnesium alloys as one side where on another end there are alloys with drastically different properties. How to weld dissimilar materials is one of the most difficult problems in welding. A difference in physicochemical properties of dissimilar joint components creates challenges for mechanically bolted assemblies as well. Due to its very low electronegative potential, magnesium is susceptible to galvanic corrosion thus affecting performance of mechanical joints in conductive environments. This chapter covers key aspects of magnesium welding and joining along with engineering applications, challenges and still existing limitations. For each technique, the typical joint characteristics and possible defects are outlined with particular attention paid to weld metallurgy and its relationship with weld strength, ductility and corrosion resistance. Although fundamentals for each technique are provided, the primary focus is on recent global activities.

The airfoil alloy IN 939 has been evaluated for the use in large aircraft engine structures. Castability trials, including sprayforming, structural welding, with electron beam (EB) and with laser, as well as repair with TIG-welding have been performed. Brazing has also been evaluated while different heat treatment schedules for pre-and post-welding and for the solution and age cycle were reviewed. Mechanical property data, tensile, creep, LCF, FCG, were established for several temperatures on material excised from large castings and on weldments. The performance of the sprayformed (SF) material was superior to the conventionally cast (CC) material but notchsensitivity was noticed in creep testing.

No abstract

Abstract It is recently conceptualized that nano-scale machining might be achieved by coupling electron emission with radiation transfer. A laser may be used to heat a workpiece to a threshold temperature, and a nano-probe might then transfer additional energy via electron emission to remove a minute amount of material. To investigate this hypothesis, a detailed numerical study is presented. The electron-beam transport is modeled using a Monte Carlo approach, and a radiation transfer model that includes Fresnel reflections is adapted to simulate laser heating. The numerical study suggests that approximately 0.5 W from a single electron-beam is sufficient to initialize local evaporation from a gold film. With the use of a laser, the required power can be halved if the film is sufficiently thin. This paper describes the details of the numerical study and establishes guidelines for such nano-scale machining processes.

No abstract

No abstract

Microfluidic devices offer the potential to automate a wide variety of chemical and biological operations that are applicable for diagnostic and therapeutic operations with higher efficiency as well as higher repeatability and reproducibility. Polymer based microfluidic devices offer particular advantages including those of cost and biocompatibility. Here, we describe direct and replication approaches for manufacturing of polymer microfluidic devices. Replications approaches require fabrication of mould or master and we describe different methods of mould manufacture, including mechanical (micro-cutting; ultrasonic machining), energy-assisted methods (electrodischarge machining, micro-electrochemical machining, laser ablation, electron beam machining, focused ion beam (FIB) machining), traditional micro-electromechanical systems (MEMS) processes, as well as mould fabrication approaches for curved surfaces. The approaches for microfluidic device fabrications are described in terms of low volume production (casting, lamination, laser ablation, 3D printing) and high-volume production (hot embossing, injection moulding, and film or sheet operations).

Early progress in machining. Electron beam machining. Ion beam machining. Electrochemical machining. Laser machining. Electrodischarge machining. Plasma arc machining. Ultrasonic machining (USM). Water-jet machining. Specialized methods of machining. Appendix. Basic atomic and electrical principles.

No abstract

A feature of radiation-beam technologies is similar processes associated with phase transformations and chemical reactions that cause changes in the volume of matter, accompanied by the vibroacoustic energy release distributed through the equipment flexible system in a wide frequency range (up to 40 kHz and high for 150 ms). The vibroacoustic signal amplitude accompanying radiation-beam technologies depends on the power density and process performance. The accelerated growth of the high-frequency components of the vibroacoustic signal is associated with the activation of the processes of volumetric boiling and evaporation/sublimation of the material. The Kf parameter, introduced as the ratio of the effective amplitudes of the low-frequency and high-frequency ranges of the vibroacoustic signal, monitors the results of high-energy flows’ impact on the material in the direction of vaporization/sublimation. The Kf parameter decrease tendency shows an increase in the proportion of the substance evaporated during laser treatment. The Kf parameter control allows the indication of the short-circuit approach in electric discharge machining, which allows increased productivity and reliability of processing. The monitoring of the Kf parameter helps to select rational processing modes, preventing excessive evaporation, providing the necessary intensity of the impact power to trigger the necessary chemical reactions in surface electron-beam alloying.

CONVENTIONS USED IN THIS BOOK Standardization Introduction to the International (SI) System of Units MACHINE TOOLS AND MACHINING OPERATIONS Introduction Generating Motions of Machine Tools Machines Using Single-Point Tools Machines Using Multipoint Tools Machines Using Abrasive Wheels Summary of Machine Tool Characteristics and Machining Equations Problems References MECHANICS OF METAL CUTTING Introduction Terms and Definitions Chip Formation The Forces Acting on the Cutting Tool and Their Measurement Specific Cutting Energy Plowing Force and the Size The Apparent Mean Shear Strength of the Work Material Chip Thickness Friction in Metal Cutting Analytical Modeling of Machining Operations Problems References TEMPERATURES IN METAL CUTTING Heat Generation in Metal Cutting Heat Transfer in a Moving Material Temperature Distribution in Metal Cutting The Measurement of Cutting Temperatures Problems References TOOL LIFE AND TOOL MATERIALS Introduction Progressive Tool Wear Forms of Wear in Metal Cutting The Tool Material Tool Geometries The Work Material High Speed Machining Hard Machining Problems References CUTTING FLUIDS AND SURFACE ROUGHNESS Cutting Fluids The Action of Coolants The Action of Lubricants Application of Cutting Fluids Cutting Fluid Maintenance Environmental Considerations Disposal of Cutting Fluids Dry Cutting and Minimum Quantity Lubrication Surface Roughness Tool Geometries for Improved Surface Finish Burr Formation in Machining Problems References ECONOMICS OF METAL-CUTTING OPERATIONS Introduction Choice of Feed Choice of Cutting Speed Tool Life for Minimum Cost and Minimum Production Time Estimation of Factors Needed to Determine Optimum Conditions Example of a Constant-Cutting-Speed Operation Machining at Maximum Efficiency Facing Operations Operations with Interrupted Cuts Economics of Various Tool Materials and Tool Designs Machinability Data Systems Limitations of Available Machinability Data Problems References NOMENCLATURE OF CUTTING TOOLS Introduction Systems of Cutting-Tool Nomenclature International Standard Problems References CHIP CONTROL Introduction Chip Breakers Prediction of Radius of Chip Curvature Prediction of Chip Breaking Performance Tool Wear During Chip Breaking Problems References MACHINE TOOL VIBRATIONS Introduction Forced Vibrations Self-Excited Vibrations (Chatter) Determination of Frequency Response Loci Dynamic Acceptance Tests for Machine Tools Improving Machine Tool Stability Problems References GRINDING Introduction The Grinding Wheel Effect of Grinding Conditions on Wheel Behavior Determination of the Density of Active Grains Testing of Grinding Wheels Dressing and Truing of Grinding Wheels Analysis of the Grinding Process Thermal Effects in Grinding Cutting Fluids in Grinding Grinding-Wheel Wear Nonconventional Grinding Operations Problems References MANUFACTURING SYSTEMS AND AUTOMATION Introduction Types of Production Types of Facilities Layout Types of Automation Transfer Machines Automatic Machines Numerically Controlled (NC) Machine Tools Comparison of the Economics of Various Automation Systems Handling of Components in Batch Production Flexible Manufacturing Systems Problems References COMPUTER-AIDED MANUFACTURING Introduction Scope of CAD/CAM Process-Planning Tasks Computer-Aided Process Planning Processing of NC Programs Computer-Aided NC Processing Numerical Control Processing Languages NC Programming Using APT-Based Languages Graphics-Based NC Processing Systems References DESIGN FOR MACHINING Introduction Standardization Choice of Work Material Shape of Work Material Shape of Component Assembly of Components Accuracy and Surface Finish Summary of Design Guidelines Cost Estimating for Machined Components Problems References NONCONVENTIONAL MACHINING PROCESSES Introduction Range of Nonconventional Machining Processes Ultrasonic Machining Water-Jet Machining Abrasive-Jet Machining Chemical Machining Electrochemical Machining Electrolytic Grinding Electrical-Discharge Machining Wire Electrical-Discharge Machining Laser-Beam Machining Electron-Beam Machining Plasma-Arc Cutting Comparative Performance of Cutting Processes Problems References NOMENCLATURE INDEX

Generation of the electron beam The behaviour of the electron beam on penetrating metal Welding parameters and advice on welding practice The weldability of metallic materials Preparation of the workpiece Beam and machine control Electron beam welding machines and equipment Quality levels and acceptable variations in electron beam welds Examples of electron beam welded components Personnel qualifications and machine testing Standards and regulations Other methods of working materials with electron beams A comparison of electron beam and laser welding.

A major challenge for additively manufactured structural parts is the low fatigue strength connected to rough as-built surfaces. In this study, Ti6Al4V manufactured with laser powder bed fusion (L-PBF) and electron beam powder bed fusion (E-PBF) have been subjected to five surface processing methods, shot peening, laser shock peening, centrifugal finishing, laser polishing and linishing, in order to increase the fatigue strength. Shot peened and centrifugal finished L-PBF material achieved comparable fatigue strength to machined material. Moreover, the surface roughness alone was found to be an insufficient indicator on the fatigue strength since subsurface defects were hidden below smooth surfaces.

Currently, the focus of additive manufacturing (AM) is shifting from simple prototyping to actual production. One driving factor of this process is the ability of AM to build geometries that are not accessible by subtractive fabrication techniques. While these techniques often call for a geometry that is easiest to manufacture, AM enables the geometry required for best performance to be built by freeing the design process from restrictions imposed by traditional machining. At the micrometer scale, the design limitations of standard fabrication techniques are even more severe. Microscale AM thus holds great potential, as confirmed by the rapid success of commercial micro-stereolithography tools as an enabling technology for a broad range of scientific applications. For metals, however, there is still no established AM solution at small scales. To tackle the limited resolution of standard metal AM methods (a few tens of micrometers at best), various new techniques aimed at the micrometer scale and below are presently under development. Here, we review these recent efforts. Specifically, we feature the techniques of direct ink writing, electrohydrodynamic printing, laser-assisted electrophoretic deposition, laser-induced forward transfer, local electroplating methods, laser-induced photoreduction and focused electron or ion beam induced deposition. Although these methods have proven to facilitate the AM of metals with feature sizes in the range of 0.1-10 µm, they are still in a prototype stage and their potential is not fully explored yet. For instance, comprehensive studies of material availability and material properties are often lacking, yet compulsory for actual applications. We address these items while critically discussing and comparing the potential of current microscale metal AM techniques.

No abstract

This study characterized properties of Ti-6Al-4V ELI (extra low interstitial, ASTM grade 23) specimens fabricated by a laser beam melting (LBM) and an electron beam melting (EBM) system for dental applications. Titanium alloy specimens were made into required size and shape for each standard test using fabrication methods. The LBM specimens were made by an LBM machine utilizing 20 µm of Ti-6Al-4V ELI powder. Ti-6Al-4V ELI specimens were also fabricated by an EBM using 40 µm of Ti-6Al-4V ELI powder (average diameter, 40 µm: Arcam AB^Ò) in a vacuum. As a control, cast Ti-6Al-4V ELI specimens (Cast) were made using a centrifugal casting machine in an MgO-based mold. Also, a wrought form of Ti-6Al-4V ELI (Wrought) was used as a control. The mechanical properties, corrosion properties and grindability (wear properties) were evaluated and data was analyzed using ANOVA and a non-parametric method (α = 0.05). The strength of the LBM and wrought specimens were similar, whereas the EBM specimens were slightly lower than those two specimens. The hardness of both the LBM and EBM specimens was similar and slightly higher than that of the cast and wrought alloys. For the higher grindability speed at 1,250 m/min, the volume loss of Ti64 LBM and EBM showed no significant differences among all the fabrication methods. LBM and EBM exhibited favorable results in fabricating dental appliances with excellent properties as found for specimens made by other fabricating methods.

used to statistically simulate the electron-beam transport; a large number of electron ensembles penetrating the workpiece surface are traced according to the material properties of the workpiece @3#. The change in the temperature of the workpiece is modeled using the Fourier heat conduction equation. Reasons for employing this equation are discussed later in the paper. Further consideration of using the Boltzmann transport equation ~BTE! in place of Fourier’s law is being considered and developed to determine the validity of the law in micro and/or nano systems @4#. The interactions between electrons and solid materials have been investigated in the literature both theoretically and experimentally @5‐7#. Particularly, Whiddington’s work @7# is important as it relates the electron penetration range Rp (m) with the electron acceleration voltage V ~Volt! and the mass density of the metal r ~kg/m 3 !, which is given as

PREFACE. Introduction. I.1 Outline of the Book. I.2 List of Symbols. I.3 Electromagnetic Fields and Potentials. I.4 Principle of Least Action. Lagrangian. Generalized Momentum. Lagrangian Equations. I.5 Hamiltonian. Hamiltonian Equations. I.6 Liouville Theorem. I.7 Emittance. Brightness. PART I ELECTRON BEAMS. 1 Motion of Electrons in External Electric and Magnetic Static Fields. 1.1 Introduction. 1.2 Energy of a Charged Particle. 1.3 Potential-Velocity Relation (Static Fields). 1.4 Electrons in a Linear Electric Field e0E kx. 1.5 Motion of Electrons in Homogeneous Static Fields. 1.6 Motion of Electrons in Weakly Inhomogeneous Static Fields. 1.6.1 Small Variations in Electromagnetic Fields Acting on Moving Charged Particles. 1.7 Motion of Electrons in Fields with Axial and Plane Symmetry. Busch's Theorem. 2 Electron Lenses. 2.1 Introduction. 2.2 Maupertuis's Principle. Electron-Optical Refractive Index. Differential Equations of Trajectories. 2.3 Differential Equations of Trajectories in Axially Symmetric Fields. 2.4 Differential Equations of Paraxial Trajectories in Axially Symmetric Fields Without a Space Charge. 2.5 Formation of Images by Paraxial Trajectories. 2.6 Electrostatic Axially Symmetric Lenses. 2.7 Magnetic Axially Symmetric Lenses. 2.8 Aberrations of Axially Symmetric Lenses. 2.9 Comparison of Electrostatic and Magnetic Lenses. Transfer Matrix of Lenses . 2.10 Quadrupole lenses. 3 Electron Beams with Self Fields. 3.1 Introduction. 3.2 Self-Consistent Equations of Steady-State Space-Charge Electron Beams. 3.3 Euler's Form of a Motion Equation. Lagrange and Poincare' Invariants of Laminar Flows. 3.4 Nonvortex Beams. Action Function. Planar Nonrelativistic Diode. Perveance. Child-Langmuir Formula. r- and T-Modes of Electron Beams. 3.5 Solutions of Self-Consistent Equations for Curvilinear Space-Charge Laminar Beams. Meltzer Flow. Planar Magnetron with an Inclined Magnetic Field. Dryden Flow. 4 Electron Guns. 4.1 Introduction. 4.2 Pierce's Synthesis Method for Gun Design. 4.3 Internal Problems of Synthesis. Relativistic Planar Diode. Cylindrical and Spherical Diodes. 4.4 External Problems of Synthesis. Cauchy Problem. 4.5 Synthesis of Electrode Systems for Two-Dimensional Curvilinear Beams with Translation Symmetry (Lomax-Kirstein Method). Magnetron Injection Gun. 4.6 Synthesis of Axially Symmetric Electrode Systems. 4.7 Electron Guns with Compressed Beams. Magnetron Injection Gun. 4.8 Explosive Emission Guns. 5 Transport of Space-Charge Beams. 5.1 Introduction. 5.2 Unrippled Axially Symmetric Nonrelativistic Beams in a Uniform Magnetic field. 5.3 Unrippled Relativistic Beams in a Uniform External Magnetic Field. 5.4 Cylindrical Beams in an Infinite Magnetic Field. 5.5 Centrifugal Electrostatic Focusing. 5.6 Paraxial-Ray Equations of Axially Symmetric Laminar Beams. 5.7 Axially Symmetric Paraxial Beams in a Uniform Magnetic Field with Arbitrary Shielding of a Cathode Magnetic Field. 5.8 Transport of Space-Charge Beams in Spatial Periodic Fields. PART II MICROWAVE VACUUM ELECTRONICS. 6 Quasistationary Microwave Devices. 6.1 Introduction. 6.2 Currents in Electron Gaps. Total Current and the Shockley-Ramo Theorem. 6.3 Admittance of a Planar Electron Gap. Electron Gap as an Oscillator. Monotron. 6.4 Equation of Stationary Oscillations of a Resonance Self-Excited Circuit. 6.5 Effects of a Space-Charge Field. Total Current Method. High-Frequency Diode in the r-Mode. Llewellyn-Peterson Equations. 7 Klystrons. 7.1 Introduction. 7.2 Velocity Modulation of an Electron beam. 7.3 Cinematic (Elementary) Theory of Bunching. 7.4 Interaction of a Bunched Current with a Catcher Field. Output Power of A Two-Cavity Klystron. 7.5 Experimental Characteristics of a Two-Resonator Amplifier and Frequency-Multiplier Klystrons. 7.6 Space-Charge Waves in Velocity-Modulated Beams. 7.7 Multicavity and Multibeam Klystron Amplifiers. 7.8 Relativistic Klystrons. 7.9 Reflex Klystrons. 8 Traveling-Wave Tubes and Backward-Wave Oscillators (O-Type Tubes). 8.1 Introduction. 8.2 Qualitative Mechanism of Bunching and Energy Output in a TWTO. 8.3 Slow-Wave Structures. 8.4 Elements of SWS Theory. 8.5 Linear Theory of a Nonrelativistic TWTO. Dispersion Equation, Gain, Effects of Nonsynchronism, Space Charge, and Loss in a Slow-Wave Structure. 8.6 Nonlinear Effects in a Nonrelativistic TWTO. Enhancement of TWTO Efficiency (Velocity Tapering, Depressed Collectors). 8.7 Basic Characteristics and Applications of Nonrelativistic TWTOs. 8.8 Backward-Wave Oscillators. 8.9 Millimeter Nonrelativistic TWTOs, BWOs, and Orotrons. 8.10 Relativistic TWTOs and BWOs. 9 Crossed-Field Amplifiers and Oscillators (M-Type Tubes). 9.1 Introduction. 9.2 Elementary Theory of a Planar MTWT. 9.3 MTWT Amplification. 9.4 M-type Injected Beam Backward-Wave Oscillators (MWO, M-Carcinotron). 9.5 Magnetrons. 9.6 Relativistic Magnetrons. 9.7 Magnetically Insulated Line Oscillators. 9.8 Crossed-Field Amplifiers. 10 Classical Electron Masers and Free Electron Lasers. 10.1 Introduction. 10.2 Spontaneous Radiation of Classical Electron Oscillators. 10.3 Stimulated Radiation of Excited Classical Electron Oscillators. 10.4 Examples of Electron Cyclotron Masers. 10.5 Resonators of Gyromonotrons (Free and Forced Oscillations). 10.6 Theory of a Gyromonotron. 10.7 Subrelativistic Gyrotrons. 10.8 Elements of Gyrotron Electron Optics. 10.9 Mode Interaction and Mode Selection in Gyrotrons. Output Power Systems. 10.10 Gyroklystrons. 10.11 Gyro-Traveling-Wave Tubes. 10.12 Applications of Gyrotrons. 10.13 Cyclotron Autoresonance Masers. 10.14 Free Electron Lasers. Appendixes. 1. Proof of the 3/2 Law for Nonrelativistic Diodes in the r-Mode. 2. Synthesis of Guns for M-Type TWTS and BWOS. 3. Magnetic Field in Axially Symmetric Systems. 4. Dispersion Characteristics of Interdigital and Comb Structures. 5. Electromagnetic Field in Planar Uniform Slow-Wave Structures. 6. Equations of Free Oscillations of Gyrotron Resonators. 7. Derivation of Eqs. (10.66) and (10.67). 8. Calculation of Fourier Coefficients in Gyrotron Equations. 9. Magnetic Systems of Gyrotrons. References. Index.

We present an axisymmetric computational model to study the heating processes of gold nanoparticles, specifically nanorods, in aqueous medium by femtosecond laser pulses. We use a two-temperature model for the particle, a heat diffusion equation for the surrounding water to describe the heat transfer processes occurring in the system, and a thermal interface conductance to describe the coupling efficiency at the particle/water interface. We investigate the characteristic time scales of various fundamental processes, including lattice heating and thermal equilibration at the particle/surroundings interface, the effects of multiple laser pulses, and the influence of nanorod orientation relative to the beam polarization on energy absorption. Our results indicate that the thermal equilibration at the particle/water interface takes approximately 500 ps, while the electron-lattice coupling is achieved at approximately 50 ps when a 48×14 nm gold nanorod is heated to a maximum temperature of 1270 K with the application of a laser pulse having 4.70 J/m(2) average fluence. Irradiation by multiple pulses arriving at 12.5 ns time intervals (80 MHz repetition rate) causes a temperature increase of no more than 3 degrees during the first few pulses with no substantial changes during the subsequent pulses. We also analyze the degree of the nanorods' heating as a function of their orientation with respect to the polarization of the incident light. Lastly, it is shown that the temperature change of a nanorod can be modeled using its volume equivalent sphere for femtosecond laser heating within 5-15% accuracy.

We present the results of 3D modeling of the laser and electron beam powder bed fusion process at the mesoscale with an in-house developed advanced multiphysical numerical tool. The hydrodynamics and thermal conductivity core of the tool is based on the lattice Boltzmann method. The numerical tool takes into account the random distributions of powder particles by size in a layer and the propagation of the laser (electron beam) with a full ray tracing (Monte Carlo) model that includes multiple reflections, phase transitions, thermal conductivity, and detailed liquid dynamics of the molten metal, influenced by evaporation of the metal and the recoil pressure. The model has been validated by a number of physical tests. We numerically demonstrate a strong dependence of the net energy absorption of the incoming heat source beam by the powder bed and melt pool on the beam power. We show the ability of our model to predict the measurable properties of a single track on a bare substrate as well as on a powder layer. We obtain good agreement with experimental data for the depth, width and shape of a track for a number of materials and a wide range of energy source parameters. We further apply our model to the simulation of the entire layer formation and demonstrate the strong dependence of the resulting layer morphology on the hatch spacing. The presented model could be very helpful for optimizing the additive process without carrying out a large number of experiments in a common trial-and-error method, developing process parameters for new materials, and assessing novel modalities of powder bed fusion additive manufacturing.

No abstract

No abstract

Metal powder bed-based Additive Manufacturing (AM) technologies, such as Electron Beam-Melting (EBM) and Laser Powder Bed Fusion (LPBF), are established in several industries due to the large design freedom and mechanical properties. While EBM and LPBF have similar operating steps, process-specific characteristics influence the component design. The differences in the energy coupling lead to differing solidification conditions, microstructures, and, thus, mechanical properties. The surface finish and geometrical accuracy are also affected. As opposed to LPBF, EBM powder layers are preheated prior to selective melting. In this study, similar volume energy densities in LPBF and EBM were used to manufacture Ti6Al4V test geometries to assess the process transferability. Since the energy coupling of LPBF and EBM differ, heat source absorption was considered when calculating the volume energy density. Even when a similar volume energy density was used, significant differences in the component quality were found in this study due to specific respective process constraints. The extent of these constrains was investigated on voluminous samples and support-free overhanging structures. Overhang angles up to 90° were manufactured with LPBF and EBM, and characterized with regard to the relative density, surface roughness, and geometric compliance.

No abstract

No abstract

No abstract

No abstract

Surface quality is still one the major issues for powder-based metal additive manufacturing, affecting in a detrimental way tribology, fatigue resistance, corrosion and many other properties in comparison to their traditionally manufactured counterparts. Therefore, post-build surface finishing is required to improve surface quality. In this work, the effectiveness of laser polishing in improving the surface quality of Ti6Al4V specimens produced with Electron Beam-Powder Bed Fusion and Laser-Powder Bed Fusion was assessed. To this aim, two independent Box-Behnken designs were created to highlight the influence that the specific surface texture produced from the two additive manufacturing techniques has on the performance of laser polishing approach, also from a statistical point of view. The surface quality variations were analysed through confocal microscopy, using the areal mean roughness, Sa, as the output parameter. Microstructure and Vickers microhardness analysis were also performed to investigate the effects of laser polishing on the surface characteristics. Within the designed and investigated laser polishing windows, the results showed that laser polishing produced an appreciable surface quality improvement, of the 52 % for the case of Laser-Powder Bed Fusion and the 68 % for the case of Electron Beam-Powder Bed Fusion. Other important outcomes are related to the notable differences of the initial roughness of the L-PBF and E-PBF parts, affecting the performance of laser polishing: Electron Beam-Powder Bed Fusion parts had a rougher profile, with an average Sa of approximately 50 μm, if compared to Laser-Powder Bed Fusion parts for which the average Sa was approximately 10 μm in the as-built condition. This condition required a different approach for the laser polishing.

The differences between the physicochemical properties of the laser and electron beam powder bed fusion (L- and EB-PBF) methods are yet to be explored further. In particular, the differences in the residual stress and phase stability of alloys with unstable phases remain unexplored. The present work is the first to systematically investigate how the heat source type and process parameters affect the surface residual stress and phase stability of an unstable β-type titanium alloy, Ti–15Mo–5Zr–3Al. The surface residual stress and β-phase behavior were studied using high-precision X-ray diffraction (HP-XRD). Significant differences were observed between the two methods. The L-PBF-made specimens exhibited tensile residual stresses of up to 400 MPa in the surface area. HP-XRD analysis revealed a stress-induced lattice distortion, interpreted as a transitional state between the β-phase and α”-phase. In contrast, the EB-PBF-made specimens showed no significant residual stress and had an undistorted β-phase coexisting with the hexagonal α-phase caused by elemental partitioning. This study provides new insights into the previously neglected effects of L-PBF and EB-PBF in unstable β-type titanium alloys.

No abstract

No abstract

A high-alloy (Cr-Mo-V) cold-work tool steel was manufactured by laser powder-bed fusion (PBF-LB) without preheating and by electron-beam powder-bed fusion (PBF-EB) with the build temperature set at 850 °C. The solidification rates, cooling, and thermal cycles that the material was subjected to during manufacturing were different in the laser powder-bed fusion than electron-beam powder-bed fusion, which resulted in very different microstructures and properties. During the solidification of the PBF-LB steel, a cellular–dendritic structure was formed. The primary cell size was 0.28–0.32 µm, corresponding to a solidification rate of 2.0–2.5 × 106 °C/s. No coarse primary carbides were observed in the microstructure. Further rapid cooling resulted in the formation of a martensitic microstructure with high amounts of retained austenite. The high-retained austenite explained the low hardness of 597 ± 38 HV. Upon solidification of the PBF-EB tool steel, dendrites with well-developed secondary arms and a carbide network in the interdendritic space were formed. Secondary dendrite arm spacing was in the range of 1.49–3.10 µm, which corresponds to solidification rates of 0.5–3.8 × 104 °C/s. Cooling after manufacturing resulted in the formation of a bainite needle-like microstructure within the dendrites with a final hardness of 701 ± 17 HV. These findings provide a background for the selection of a manufacturing method and the development of the post-treatment of a steel to obtain a desirable final microstructure, which ensures that the final tool’s performance is up to specification.

Additively manufactured metal parts often have a high level of residual stress and can exhibit complex crystalline phase properties due to the rapid cooling nature of their fabrication process. X-ray diffraction (XRD) is a non-destructive technique that can characterize both the residual stress and the crystalline phase properties in detail. However, XRD is an ex-situ measurement and provides only the final state of the manufactured parts. In this article, a method that combines the XRD analyses and numerical simulation of the thermal history during the manufacturing process is reviewed with two examples of titanium alloys fabricated by laser and electron beam powder fusion techniques.

Additive manufacturing (AM) is a novel method of manufacturing parts directly from digital model by using layer-by-layer material build-up approach. This tool-less manufacturing method can produce fully dense metallic parts in short time with high precision. Features of AM like freedom of part design, part complexity, light weighting, part consolidation, and design for function are garnering particular interests in metal AM for aerospace, oil and gas, marine and automobile applications. Powder bed fusion, in which each powder bed layer is selectively fused using energy source like laser or electron beam, is the most promising AM technology that can be used for manufacturing small, low volume, and complex metallic parts. This review presents evolution, current status, and challenges of powder bed fusion technology. It also compares laser and electron beam-based technologies in terms of performance characteristics of each process, advantages/disadvantages, materials, and applications.

No abstract

Many standard welding processes, such as gas metal arc-, laser-, or electron-beam welding, can be used for additive manufacturing (AM) with only slight adaptions. Wire-based additive manufacturing provides an interesting alternative to powder-based processes due to their simplicity and comparatively high deposition rates. The use of an electron beam as heat source for AM offers unique possibilities for construction of components due to its inherent flexibility. It is possible to efficiently build bigger parts with comparably fine features and high complexity. Furthermore, additional working steps such as preheating, surface modification, welding, or heat treatments can be implemented into the additive manufacturing process and thereby alleviate the bottleneck of the evacuation of the vacuum chamber. Aside from this, the ultra high vacuum atmosphere can be beneficial, when working with reactive materials such as Ti or Mo. The intrinsic complexity of electron-beam additive manufacturing (EBAM) can make a stable and reproducible process control quite challenging. In this study, the influence of the main process parameters, such as heat input, energy distribution, wire feed, and their complex interactions are investigated. Based on single beads on a mild steel substrate using an unalloyed metal core wire (G4Si1), the correlation between the process parameters such as beam current, acceleration voltage, speed, wire feed rate and position, and the resulting bead geometry, height, width and penetration was studied. These findings were used to successfully establish a multi pass layout consisting of one to six beads next to each other and up to ten layers in height. For basic characterization, metallographic analysis as well as hardness measurements were performed.

No abstract

No abstract

In recent years, the field of micro- and nanochannel fabrication has seen significant advancements driven by the need for precision in biomedical, environmental, and industrial applications. This review provides a comprehensive analysis of emerging fabrication technologies, including photolithography, soft lithography, 3D printing, electron-beam lithography (EBL), wet/dry etching, injection molding, focused ion beam (FIB) milling, laser micromachining, and micro-milling. Each of these methods offers unique advantages in terms of scalability, precision, and cost-effectiveness, enabling the creation of highly customized micro- and nanochannel structures. Challenges related to scalability, resolution, and the high cost of traditional techniques are addressed through innovations such as deep reactive ion etching (DRIE) and multipass micro-milling. This paper also explores the application potential of these technologies in areas such as lab-on-a-chip devices, biomedical diagnostics, and energy-efficient cooling systems. With continued research and technological refinement, these methods are poised to significantly impact the future of microfluidic and nanofluidic systems.

Here, we demonstrate a new level of precision in measuring melting temperatures at high pressure using laser flash-heating followed by Scanning Electron Microscopy and Focused Ion Beam Milling. Furthermore, the new measurements on tantalum put unprecedented constraints on its highly debated melting slope, calling for a reevaluation of theoretical, shock compression and diamond cell approaches to determine melting at high pressure. X-ray analysis of the recovered samples confirmed the absence of chemical reactions, which likely played a significant role in previous experiments.

One of the challenges for metasurface research is upscaling. The conventional methods for fabrication of metasurfaces, such as electron-beam or focused ion beam lithography, are not scalable. The use of ultraviolet steppers or nanoimprinting still requires large-size masks or stamps, which are costly and challenging in further handling. This work demonstrates a cost-effective and lithography-free method for printing optical metasurfaces. It is based on resonant absorption of laser light in an optical cavity formed by a multilayer structure of ultrathin metal and dielectric coatings. A nearly perfect light absorption is obtained via interferometric control of absorption and operating around a critical coupling condition. Controlled by the laser power, the surface undergoes a structural transition from random, semiperiodic, and periodic to amorphous patterns with nanoscale precision. The reliability, upscaling, and subwavelength resolution of this approach are demonstrated by realizing metasurfaces for structural colors, optical holograms, and diffractive optical elements.

No abstract

Micro- and nano-scale devices are used in electronics, micro-electro- mechanical, bio-analytical and medical components. An essential step for the fabrication of such small scale devices is photolithography. Photolithography requires a master mask to transfer micrometre or sub-micrometre scale patterns onto a substrate. The requirement of a physical, rigid mask can impede progress in applications which require rapid prototyping, flexible substrates, multiple alignment and 3D fabrication. Alternative technologies, which do not require the use of a physical mask, are suitable for these applications. In this paper mask-less methods of micro- and nano-scale fabrication have been discussed. The most common technique, which is the laser direct imaging (LDI), technique has been applied to fabricate micrometre scale structures on printed circuit boards, glass and epoxy. LDI can be combined with chemical methods to deposit metals, inorganic materials as well as some organic entities at the micrometre scale. Inkjet technology can be used to fabricate micrometre patterns of etch resists, organic transistors as well as arrays for bioanalysis. Electrohydrodynamic atomisation is used to fabricate micrometre scale ceramic features. Electrochemical methodologies offer a variety of technical solutions for micro- and nano-fabrication owing to the fact that electron charge transfer can be constrained to a solid–liquid interface. Electrochemical printing is an adaptation of inkjet printing which can be used for rapid prototyping of metallic circuits. Micro-machining using nano-second voltage pulses have been used to fabricate high precision features on metals and semiconductors. Optimisation of reactor, electrochemistry and fluid flow (EnFACE) has also been employed to transfer micrometre scale patterns on a copper substrate. Nano-scale features have been fabricated by using specialised tools such as scanning tunnelling microscopy, atomic force microscopy and focused ion beam. The methodologies adopted for nano-fabrication have analogies with the micrometre scale patterning methods. Currently, the resolution of mask-less techniques is lower than that of lithographic methods using a physical mask. However, in future, hybridisation or combination of the mask-less methods could lead to high resolution and higher precision micro- and nano-scale patterning methods.