Effects of Build Orientations on Microstructure Evolution, Porosity Formation, and Mechanical Performance of Selective Laser Melted 17-4 PH Stainless Steel

Abstract

In this study, the effect of phase, microstructure, and porosity in Selective Laser Melting (SLM) on hardness, tensile, and fracture behavior of 17-4 PH was investigated. The increasing interest in SLM in producing complex parts has encouraged the industry to produce performance parts, such as martensitic 17-4 PH stainless steel. However, the microstructure and mechanical behavior of SLM 17-4PH is not fully understood by researchers. Understanding the microstructure profile is complex because it is driven by thermal history and porosity. Both elements vary, based on the build directions, further hindering researchers from fully understanding the mechanical properties. To fabricate specimens in three different building orientations (0°, 45°, and 90°), 17-4 powder was used. Two phases, namely, austenite and martensite, with 90° build direction, retained more austenite, due to the reheating process on a smaller base area. The optical microstructure revealed several elements that were distinct for SLM processing, including circular, columnar lath, wave melt pool, and porosity. Columnar lath was found to grow continuously across different melt pools. Hardness was found to be higher for 0° than for 90°, due to higher martensite content. Tensile strength was highest for 0°, at 958 MPa, higher than at 45° and 90° at 743 and 614 MPa, respectively. Porosity analysis validated that 90° had all three types of porosities and, specifically, the crescent type, which held un-melted powders. All types of porosities were found in fractography analysis.

Shot Peening Effect on Sliding Wear in 0.9% NaCl of Additively Manufactured 17-4PH Steel

“…GP1 gas-atomized powder by EOS GmbH (Krailling, Germany) was also used for fabrication with the following process parameters: the laser power was 200 W, the thickness of the sinter layer was 0.02 mm, the laser spot size was 0.1 mm and the scan speed 1000 mm/s. Following Equation (1), shown in [ 29 ], the calculated energy density for this research was 100 J/mm 2 : where the symbols are as follows: energy input per volume ( E ), energy density (J/mm 2 ), P , laser power (W), V , scanning, speed (mm/s), t , layer thickness (mm), h , hatch spacing (mm). Nitrogen was used as a shielding gas during fabrication.…”

“…The heat treatment process was carried out for the matrix together with the specimens in a Nabertherm GmbH (Lilienthal, Germany) model N41/H chamber furnace dedicated to annealing after sintering. The orientation of the print can affect the microstructure and mechanical properties of fabricated components of 17-4PH steel [ 29 , 30 ]. Therefore, in our case, the samples were fabricated in repeatable conditions, as shown in Figure 1 .…”

“…GP1 gas-atomized powder by EOS GmbH (Krailling, Germany) was also used for fabrication with the following process parameters: the laser power was 200 W, the thickness of the sinter layer was 0.02 mm, the laser spot size was 0.1 mm and the scan speed 1000 mm/s. Following Equation (1), shown in [29], the calculated energy density for this research was 100 J/mm 2 :…”

“…Materials 2024, 17, x FOR PEER REVIEW 4 of 17 the print can affect the microstructure and mechanical properties of fabricated components of 17-4PH steel [29,30]. Therefore, in our case, the samples were fabricated in repeatable conditions, as shown in Figure 1.…”

Role of laser power and scan speed combination on the surface quality of additive manufactured nickel-based superalloy

“…From the previous studies it was observed that, with regards to the as-built surface quality of IN718, the presence of partially melted powder particles, surface voids, porosity, unstable melt pool, spattering of molten droplets and balling are the significant factors that directly alter the surface roughness. [26][27][28] The sticking of partly melted powders on the surface of L-PBF-manufactured components is one of the primary causes of surface roughness. 29,30 The periodic bumps between the neighboring scan tracks and melt pool irregularities on the top surface also cause surface roughness.…”