In this study, the microstructures and mechanical properties of Inconel 718 fabricated from selective laser melting (SLM) process were experimentally investigated. Specimens with different build heights were prepared for microstructural observations by optical microscopy and scanning electron microscope. The texture evolution was also examined using electron backscatter diffraction (EBSD). In general, columnar γ dendrites are found along the build direction from the X-plane (side surface), while the microstructure of Z-plane (scanning surface) is characterized by equiaxed grains. The microstructures vary along the build height: the top layers present coarse columnar dendrites while the bottom layers show much narrower columnar dendrites owing to a higher cooling rate. The top layers also present the combination of a γ matrix and a higher percentage of the Laves phase, while the bottom layers show a much less Laves phase due to, again, a higher cooling rate. Random textures are shown for the SLM Inconel 718 samples. Nanoindentation tests identify the Young’s modulus and hardness of about 200 GPa and 7 GPa, respectivley.

This study presents a thorough literature review on the powder-bed laser additive manufacturing processes such as selective laser melting (SLM) of Inconel 718 parts. The paper first introduces the general aspects of powder-bed laser additive manufacturing and then discusses the unique characteristics and advantages of SLM. Moreover, the bulk of this study includes extensive discussions of microstructures and mechanical properties, together with the application ranges, of Inconel 718 parts fabricated by SLM.

In this paper, the process parameter effects on the thermal characteristics in powder-bed electron beam additive manufacturing (EBAM) using Ti-6Al-4V powder were investigated. The machine-specific setting, called “speed function” (SF) index that controls the beam speed and the beam current during a build, was utilized to evaluate the beam scanning speed effects. EBAM parts were fabricated using different levels of SF index (20 to 65) and build surface morphology and part microstructures were examined. A near infrared (NIR) thermal imager was used for temperatures measurements during the EBAM process. In addition, a thermal model previously developed was employed for temperature predictions and comparison with the experimental results. The major results are summarized as follows. The SF index noticeably affects the thermal characteristics in EBAM, e.g., a melt pool length of 1.72 mm vs. 1.26 mm for SF20 and SF65, respectively, at the 24.43 mm build height. This is because the higher the speed function index, the higher the beam speed, which reduces the energy density input and results in a lower process temperature. For the surface conditions and part microstructures, in general, a higher SF index tends to produce parts of rougher surfaces with more residual porosity features and large β grain columnar widths.

In this study, the microstructure analysis and nanoindentation characterization from electron beam additive manufacturing (EBAM) were experimentally investigated. Specimens with different build heights of an EBAM built part were tested for microstructure observations by optical microscopy and scanning electron microscopy. The correspondent Young’s modulus and hardness were measured by nanoindentation. Columnar prior β structure is found along the build direction from the X-plane, while the Z-plane is characterized by equiaxed grains and fine Widmanstätten (α+β) structure. The microstructure varies along the build height: the top layers present finer columnar prior β grains and inside Widmanstätten (α+β) structure, while the bottom layers show bigger percentage of α′ martensitic phase owing to the very high cooling rate. Nanoindentation tests identify the highest Young’s modulus of 127.9 GPa and hardness of 6.5 GPa from the top layers of Z-plane. The Young’s modulus and hardness of the middle layers are lower because of the repeated heating. The Z-plane shows higher mechanical properties compared to that of the X-plane. The enhancement of modulus and hardness of the Ti-6Al-4V alloy could be attributed to the strengthening phase of α′ and fine microstructure.

In the powder-based electron beam additive manufacturing (EBAM) process, preheating is applied, prior to the melting stage, to aggregate precursor powders and to reduce the residual stresses in the build parts. Preheating results in sintering of the powders, which serve as the initial work material for the subsequent melting stage. In this study, sintered Ti-6Al-4V alloy powders from preheating were obtained and studied. The specimens of sintered powders, also processed to prepare metallographic samples, were observed and characterized by optical microscopy (OM) and scanning electron microscopy (SEM). The results show that after preheating, some powders are partially “melted” and necks between adjacent particles are formed with metallurgical bonds. The sintering evidence, necking, can be noted on both the build plane and the side surface (normal to the build plane). The Baktetwave α-β structure is identified in the powders, while the martensitic structure is formed in the solid EBAM part.

This paper presents a thorough literature review of the powder-based electron beam additive manufacturing (EBAM) technology. EBAM, a relatively new additive manufacturing (AM) process, can produce full-density metallic parts directly from the electronic data of the designed part geometry. EBAM has gained broad attentions from different industries such as aerospace and biomedical, with great potential in a variety of applications. The paper first introduces the general aspects of EBAM. The unique characteristics, advantages and challenges of EBAM are then presented. Moreover, the hub of this paper includes extensive discussions of microstructures, mechanical properties, geometric attributes, which impact the application ranges of EBAM parts, with focus on commonly used titanium alloys (in particular, Ti-6Al-4V). In the end, modeling work of the EBAM process is discussed as well.

In machining using a diamond-coated tool, the tool geometry and process parameters have compound effects on the thermal and mechanical states in the tools. For example, decreasing the edge radius tends to increase deposition-induced residual stresses at the tool edge interface. Moreover, changing the uncut chip thickness to a small-value range, comparable or smaller than the edge radius, will involve the so-called size effect. In this study, a developed 2D cutting simulation that incorporates deposition residual stresses was applied to evaluate the size effect, at different cutting speeds, on the tool stresses, tool temperatures, specific cutting energy as well as the interface stresses around a cutting edge. The size effect on the radial normal stress is more noticeable at a low speed. In particular, a large uncut chip thickness has a substantially lower stress. On the other hand, the size effect on the circumferential normal stress is more noticeable at a high speed. At a small uncut chip thickness, the stress is largely compressive.