Anisotropic microstructure and mechanical properties of additively manufactured Co-Cr-Mo alloy using selective electron beam melting for orthopedic implants

Co-Cr-Mo alloy is used extensively for orthopedic implant applications. In this work, anisotropy in microstructure and mechanical properties of additively manufactured Co-Cr-Mo alloy by selective electron beam melting (SEBM) has been investigated. Experimental results show that the SEBM-built Co-Cr-Mo parts along the build direction would be preferred over that of the non-build direction in strength and elongation. Strong anisotropy in tensile properties was found for the SEBM-built Co-Cr-Mo parts in two different directions. The microstructure of SEBM-built Co-Cr-Mo alloys consists of face-centered cubic columnar grains with the < 001 > preferred orientation and continuous thin carbide films at the grain boundaries. Columnar grains are supposed to be the basic microstructure feature that results in poor mechanical performance in the non-build direction. However, continuous thin carbide films at columnar grain boundaries severely exaggerate the anisotropic characteristics, which is the dominant reason for anisotropy. It is suggested that the SEBM-built Co-Cr-Mo along the build direction is expected to be suitable for load-bearing orthopedic implants.