Effect of phase transformation on the mechanical properties of the Co-Cr-Mo alloy fabricated by selective laser melting

• Published in: Materials characterization Vol. 186; p. 111767
• Main Authors: Im, Hyeon-Tae, Kim, Dae Ha, Kim, Young Do, Fadonougbo, Julien O., Mo, Chan Bin, Park, Jae-Young, Park, Ki Beom, Kang, Jang-Won, Kang, Hyun-Su, Park, Hyung-Ki
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01-04-2022
• Subjects: Co-Cr-Mo alloy; Phase transformation; Residual stress; Selective laser melting; Stress relief annealing; Phase transformation; Stress relief annealing; Selective laser melting; Co-Cr-Mo alloy; Residual stress
• ISSN: 1044-5803; 1873-4189
• DOI: 10.1016/j.matchar.2022.111767

In this study, we examined the effect of stress relief annealing (SRA) temperatures on the microstructure and mechanical behavior of a Co-Cr-Mo alloy fabricated by selective laser melting (SLM). For the SRA, the as-built SLM samples were annealed at 750 °C and 1050 °C. In the as built SLM sample, the γ phase was mainly formed, but some ε phases were present together. The percentage of the ε phase increased significantly after SRA at 750 °C, and a microstructure with a 100% γ phase formed after SRA at 1050 °C. Changes in mechanical properties were characterized by an increase in both hardness and yield strength, while the elongation decreased after SRA at 750 °C. This was caused by the formation of the ε phase, which possesses high strength and hardness but brittleness. After SRA at 1050 °C, the hardness and yield strength decreased, and the elongation increased compared to the as-built SLM sample because of the decrease in the residual stress. In the γ phase of the Co-Cr-Mo alloy, strain-induced γ to ε martensitic transformation occurring during deformation, and it was more marked in the as-built SLM sample with high residual stress. Therefore, when the as-built sample was deformed, the brittle ε phase formed more rapidly than in the sample after SRA at 1050 °C, resulting in low elongation.
•The effect of SRA on the microstructure and mechanical properties of CCM alloy fabricated by SLM was investigated.•The phase transformation behavior was changed according to the SRA temperature.•The mechanical properties were affected by the microstructure change after SRA.•After SRA, the residual stress was reduced by the heat treatment effect.