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 gamma-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 degrees 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.

Automated summary

This study investigates a commercial Co-Cr-Mo alloy fabricated by laser powder bed fusion in terms of microstructure, crack formation, mechanical properties, and residual stresses. The anisotropic microstructure of the as-built samples is influenced by the heat flow condition along the building direction. The presence of voids and coarsened secondary particles at the grain boundaries leads to reduced tensile properties after heat treatment.