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.