Effect of Ti addition on microstructure and mechanical properties of Co-Cr-Mo alloy developed by µ-plasma arc metal powder additive manufacturing process.

This paper presents effects of addition of 4wt.% of Ti to Co-Cr-Mo alloy by µ-plasma arc metal powder additive manufacturing (µ-PAMPAM) process on microstructure, phase evolution, bending strength, tensile and compressive yield and ultimate strength, % elongation, microhardness, porosity, and density of the resultant alloy and their comparison with Co-Cr-Mo alloy. Microstructure and phase evolution study of Co-Cr-Mo alloy showed Co-rich matrix comprising of γ-Co and ε-Co phases, formation of Cr7C3 and Cr23C6 carbides due to presence of carbon and affinity of Cr towards it, and micro-cracks. Addition of 4 wt% Ti to Co-Cr-Mo alloy refined its grains, minimized formation of micro-cracks, led to formation of β-Ti phase and Co-Ti intermetallic compound along with the chromium carbides. It also reduced porosity and density of the resultant Co-Cr-Mo-4Ti alloy. Grain refinement increased flexural strength of Co-Cr-Mo-4Ti alloy. Solid solution effect of Ti increased tensile and compressive yield strength, ultimate compressive and tensile strength, and percentage elongation of Co-Cr-Mo-4Ti alloy as compared to Co-Cr-Mo alloy. Microhardness of Co-Cr-Mo-4Ti alloy increased to 473 MPa from 382 MPa of Co-Cr-Mo alloy due to formation of Co-Ti intermetallic compound and β-Ti phase. All these improvements enhance durability and strength of Co-Cr-Mo-4Ti alloy along with a reduction in stress shielding effect as compared to the Co-Cr-Mo, making it more suitable for knee prothesis applications.