Co–Cr–Mo alloy fabricated by laser powder bed fusion process: grain structure, defect formation, and mechanical properties

In this work, a commercial Co–Cr–Mo alloy fabricated by laser powder bed fusion (LBPF) was studied from the point of view of the microstructure of the as-built material, crack mechanism formation, mechanical properties, and residual stresses. Correlative characterization encompassing X-ray diffraction, optical and scanning electron microscopy supported by electron backscattered diffraction, nanoindentation, tensile testing, and residual stresses measurements were performed on the as-built and heat-treated samples. The anisotropic microstructure of the as-built Co–Cr–Mo samples is imposed by the heat flow condition along the building direction (BD), parallel to the z-axis. Cracks and pores were found at the cellular dendrite boundaries and grain boundaries. Only diffraction peaks corresponding to γ-Co (FCC) were observed through X-ray diffraction. The formation of M₂₃C₆ carbides was experimentally confirmed by electron backscatter diffraction analysis and predicted by the non-equilibrium solidification path simulation. After the Co–Cr–Mo alloy was heat-treated at 1050 °C for 2 h, the previous cellular structures were dissolved. The tensile properties of the heat-treated samples were reduced due to the microstructural heterogeneities such as voids together with coarsened secondary particles that existed at the grain boundaries.