Fatigue Data for Laser Powder Bed Fused 17-4 PH Stainless Steel Specimens in Different Heat Treatment and Surface Roughness Conditions

This article presents the data demonstrating the synergistic effect of surface roughness and heat treatment on the fatigue behavior of 17–4 PH stainless steel (SS) fabricated via Laser Powder Bed fusion (L-PBF). Two sets of specimens, in as-built and machined surface conditions, were heat treated using five different recommended procedures for 17-4 PH SS by ASTM. Axial fully-reversed fatigue tests (R = -1) were conducted on heat treated as-built and machined specimens. The stable hysteresis stress–strain data, as well as the maximum and minimum stress and strain values for the cycle in a log10 increment are included for all conducted fatigue experiments. In addition, fractography images are provided for selected set of specimens

Effect of Preheating Build Platform on Microstructure and Mechanical Properties of Additively Manufactured 316L Stainless Steel

This study aims to understand the effect of build platform preheating on the microstructural features and mechanical properties of 316L stainless steel (SS) fabricated via laser beam powder bed fusion (LB-PBF) process. Two sets of specimens were fabricated on a non-preheated build platform and the build platform preheated to 150 °C. Thermal simulations are carried out using ANSYS using additive manufacturing module to investigate the variation in thermal history experienced by the specimens in each condition. Microstructural features are analyzed via simulation, and the results are validated experimentally. In addition, the effect of preheating on the porosity size and distribution is evaluated using digital optical microscopy. Mechanical properties of specimens from each condition are further assessed and correlated to the variations in microstructure and defect size distributions.Mechanical Engineerin

A Comparative Study on the Microstructure and Texture Evolution of L-PBF and LP-DED 17-4 PH Stainless Steel during Heat Treatment

This study aims to characterize the microstructure and crystallographic texture of 17-4 PH stainless steel (SS) manufactured with laser powder directed energy deposition (LP-DED) and laser powder bed fusion (L-PBF), in both non-heat treated and heat treated conditions. It is found that the non-heat treated LP-DED 17-4 PH SS possesses coarse columnar ferrite grains decorated with Widmanstätten ferrite grains, whereas the L-PBF counterpart has very fine and mostly equiaxed ferrite grains along with lath martensite. An identical stress relief (SR) temperature is obtained for both the L-PBF and LP-DED 17-4 PH SS samples based on the phase diagrams generated using Thermo-Calc. software. The SR step prior to CA-H1025 heat treatment resulted in texture weakening and slightly refined the grain structure. The non-heat treated L-PBF 17-4 PH SS sample possesses strong cube and γ-fiber textures, while the texture transfers to weaker γ-fiber components after performing SR-CA-H1025 heat treatment.Mechanical Engineerin

Fatigue Behavior of Laser Beam Directed Energy Deposited Inconel 718 at Elevated Temperature

Nickle based super alloys such as Inconel 718 are being extensively used to manufacture turbine blades for jet engines due to their superior mechanical properties at higher working temperatures. Furthermore, poor machinability associated with Inconel 718 also makes it an attractive material for additive manufacturing processes, which possess the capability to fabricate near net shaped parts. Hence, in this study, the fatigue behavior of Inconel 718 fabricated using laser beam directed energy deposition (LB-DED) is investigated under strain-controlled, fully-reversed conditions at an elevated temperature of 650° C. Fractography analysis was conducted to determine the failure mechanism for additive manufactured Inconel 718 due to higher working temperatures. The results obtained from the fatigue and fractography analysis were then compared with the results obtained from fatigue tests conducted at room temperature. At elevated test temperature, LB-DED Inconel 718 specimens exhibited lower fatigue resistance compared to the tests conducted at the room temperature, primarily in the low cycle fatigue regime. Whereas, in the high cycle fatigue regime the effect of test temperature was observed to be minimal. Furthermore, secondary cracks resulting from the formation of brittle behaving precipitates on the grain boundaries was also evident from the fractography analysis indicating significant changes in the microstructural features of LB-DED Inconel 718 as a consequence of elevated test temperature.Mechanical Engineerin

Effect of Heat Treatment on the Tensile Behavior of 17-4 PH Stainless Steel Additively Manufactured by Metal Binder Jetting

Metal Binder Jetting (MBJ), a non-fusion-based powder bed additive manufacturing (AM) process, enables the fabrication of complex geometries with minimum residual stresses. Various materials have been successfully manufactured via the MBJ process; however, appropriate post-process heat treatments are required to enhance their mechanical performance as compared to the wrought or other additively manufactured counterparts. This study aims to investigate the effect of post-manufacture heat treatment on the microstructure and mechanical properties of MBJ 17-4 PH stainless steel (SS). Various heat treatment procedures following the standard routes for the wrought 17-4 PH SS are conducted to evaluate their effects on the tensile behavior of MBJ 17-4 PH SS. The mechanical behavior of the MBJ 17-4 PH SS in various heat treatment conditions is discussed based on their corresponding microstructure.Mechanical Engineerin

High cycle fatigue behavior and life prediction for additively manufactured 17-4 PH stainless steel: Effect of sub-surface porosity and surface roughness

The high potential of additive manufacturing (AM) techniques offers novel opportunities and unexplored design freedom. However, typical internal defects and poor surface quality inherent to AM process not only cause a lower fatigue resistance, but also more scatter in fatigue data; thus, hindering adoption of AM to fatigue critical applications. This study investigates the effect of surface quality and sub-surface porosity on high cycle fatigue behavior of 17-4 precipitation hardening (PH) stainless steel (SS) fabricated using laser beam powder bed fusion (LB-PBF) process. Parts were fabricated in three conditions: net-shape (NS) specimens, oversized specimens, and cylindrical rods. The oversized specimens and cylindrical rods were, respectively, further shallow machined (SM) and deep machined (DM) to the dimensions and geometry of net-shape specimens. The population of defects was investigated via optical microscopy of polished sections, X-ray micro-CT scan analysis, and fractography of fracture surfaces after fatigue tests. The fatigue crack growth (FCG) properties were generated at three stress ratios of R=-1,0.1,0.7 to determine the Kitagawa-Takahashi diagram and propagation curve. The polished sections showed the presence of large sub-surface, close-to-surface pores in the NS specimens, while SM and DM conditions had smaller and more uniformly distributed porosity. Critical defects detected on the fracture surfaces were small pores in machined specimens, and relatively large surface irregularities in NS specimens. Machining process, both in SM and DM conditions, enhanced the fatigue performance of the material as compared to that of NS condition. However, in terms of level of machining allowance, no further enhancement in fatigue performance was observed for DM specimens as compared to that of SM ones. Fatigue assessment for both net-shape and machined conditions was obtained performing FCG simulations based on the typical surface features and volumetric defects. Simulation results yielded correct estimates for both net-shape and machined specimens

The Effects of Powder Recycling on the Mechanical Properties of Additively Manufactured 17-4 PH Stainless Steel

The booming interest in Additive Manufacturing (AM), is seeing a rising number of industries and research entities adopting this technology into their manufacturing practices. Of particular interest is Laser Powder Bed Fusion (L-PBF) process, a common AM method for fabricating metallic components. However, one obstacle is the high cost of powder feedstock. A popular tactic to offset this cost is to reuse the powder between prints, but there is no in-depth understanding of how the powder feedstock may change or affect the mechanical properties of the produced parts. By incorporating unique powder/part characterization methods, this study quantifies the rheological properties of continually recycled 17-4 precipitation hardening (PH) stainless steel (SS) powder through successive printing of mechanical test specimens. The AM specimens are subjected to tensile tests, to correlate mechanical behavior to changing powder quality, including particle size/shape distribution, flowability, and density.Mechanical Engineerin