Role of aging induced alpha precipitation on the mechanical and tribocorrosive performance of a beta Ti-Nb-Ta-O orthopedic alloy

A low modulus beta Ti-Nb-Ta-O alloy was subjected to heat treatment to investigate its phase stability upon aging. The resultant effect on the mechanical and functional properties was systematically evaluated. The aging of the beta-only microstructure, obtained by solutionizing and quenching, resulted in the formation of ultrafine alpha-precipitates with increasing order of size as the aging temperature increased from 400 degrees C to 600 degrees C. The variation in the size of alpha-precipitates effected the mechanical properties at the three different aging temperature. The highest hardening observed at 400 degrees C was associated with macroscopic embrittlement, whereas age softening was observed in samples aged at 600 degrees C due to coarsening of precipitates and softening of the beta-matrix. In contrast, aging at 500 degrees C resulted in about 32% increase in tensile strength from the beta-solutionized condition. As the samples aged at 500 degrees C showed optimum combination of mechanical properties among the aged samples, these were further characterized for their electrochemical, tribological and biological responses. The fretting wear studies showed that the wear rate of the solution-treated samples increased after aging due to the higher corrosion rate leading to a higher rate of tribocorrosive dissolution and formation of a transfer layer harder than that of solution treated sample. The Ti-Nb-Ta-O alloy supported the attachment and proliferation of osteoblasts similar to that on commercially pure Ti. Taken together, this work provides new insights into the preparation of next-generation Ti alloys for biomedical applications with high strength and low modulus through microstructural control induced by heat treatment.