Effects of heat treatment on the microstructure and properties of a face-centered cubic CoCrMoW alloy prepared via laser powder bed fusion

The laser powder bed fusion (LPBF) process allows for the production of metals and alloys with intricate substructures including cell boundaries, stacking faults and dislocations, which can serve as nucleation sites for precipitation upon heat treatment, enabling the precipitation control for superior properties. In this study, a biomedical face-centered cubic Co25Cr5Mo5W alloy with dense cell boundaries and stacking faults was fabricated by LPBF, which exhibited exceptional tensile properties with a yield strength of ∼ 820 MPa and an elongation of ∼ 22.3%. Subsequently, the as-built alloy samples were heat-treated at 700 °C, 900 °C and 1100 °C for 1 h, respectively, to reveal the elemental diffusion and precipitation behaviors at different temperatures and their influence on the properties. Comprehensive microstructure analysis revealed distinct elemental diffusion behaviors and resulting properties among the three heat-treated specimen groups. The 700 °C heat-treated specimen exhibited noticeable elemental segregation at cellular sub-grain boundaries, without significant precipitation within the cellular sub-grains even with extended heat treatment time. The 900 °C heat-treated specimen displayed fine and dense Co ₃(Mo,W) ₂ Si precipitates dispersed throughout the specimen, enhancing the yield strength to ∼ 1170 MPa while maintaining a decent ductility of ∼ 7.5%. Conversely, the 1100 °C heat-treated specimen exhibited larger precipitates with sparser distribution, leading to reduced strength and ductility. Additionally, the 900 °C heat-treated specimen exhibited excellent corrosion resistance.