Application of Harmonic Structure Design to Biomedical Co-Cr-Mo Alloy for Improved Mechanical Properties

Harmonic structure is a recently introduced concept for material microstructure design. It is essentially a bimodal microstructure in which deliberately introduced structural heterogeneity has a specific order: interconnected network of ultra-fine grained (UFG) regions, called "shell area", and coarse-grained regions called "core area". Such microstructural features dictate a unique set of properties to the Harmonic-structured materials. The present paper deals with the application of harmonic structure design to biomedical Co-Cr-Mo alloys for improved mechanical properties. In the present work, it has been demonstrated that full density Co-Cr-Mo alloy compacts with harmonic structure can be successfully prepared by controlled mechanical milling followed by spark plasma sintering of the pre-alloyed powders at 1323 K for 3.6 ks. Sintered compacts exhibited an excellent combination of strength and ductility. Moreover, it has been also shown that the mechanical properties depend strongly on the volume fraction of the inter-connected three-dimensional network of fine-grained regions, i.e., shell volume fraction. In addition, the plastic deformation of harmonic structure Co-Cr-Mo alloy also led to alpha-FCC to epsilon-HCP allotropic transformation. Therefore, the application of harmonic structure design leads to the new generation microstructure of biomedical Co-Cr-Mo alloys, which demonstrates outstanding mechanical properties compared to conventional materials.