Water-atomized and gas-atomized 17-4 PH stainless steel powder were used as feedstock to manufacture components by selective laser melting process and applying laser energy density of 64 and 104 J/mm3. Gas atomized powder revealed only martensitic phase after printing and heat treatment at both energy density. As-printed water atomized powder contained both martensitic and austenitic phase regardless of energy density. After solutionizing at 1051ºC and aging at 482 ºC, austenitic phase was observed in water atomized powder printed at higher laser energy density of 104 J/mm3. This could be perhaps due to higher carbon content in water-atomized powder and dissolutions of these carbon at higher energy density of 104 J/mm3, local enrichment of austenite stabilizer element and reverse austenite formation. The H900 heat treatment cycle was not effective in enhancing mechanical properties of the water atomized powder after laser melting. After solutionizing at 1315ºC and aging at 482ºC fully martensitic structure was observed with hardness (40.2 HRC), yield strength (1000 MPa) and ultimate tensile strength (1261 MPa) comparable to those of gas atomized (42.7 HRC, 1254 MPa and 1300 MPa) and wrought alloy (39 HRC, 1170 MPa and 1310 MPa), respectively. Higher elongation in water atomized powder (5.5%) was related to finer martensite grain size. Water atomize powder had one order of magnitude higher carbon content compared to gas atomized powder that could get dissolved at 1315ºC and lead to formation of finer martensite, precipitation of carbides along with Cu-enriched carbides.
- Demonstrate the role of powder feedstock on materials properties during SLM
- Define the post processing for water atomized 17-4 PH powder to get similar results to gas powder
- Describe the role of particle size distribution and laser energy density on materials properties