Effect of Solution Treatment on Microstructure and Mechanical Hardness of Ti-6Al-7Nb

Abstract

The metastable β Ti-6Al-4V alloy has been used clinically as a permanent implant material owing to its suitable mechanical properties and biocompatibility. However, the alloying element V was accused of causing toxicity when released to human body fluid. In this work, Nb was used in the alloy to replace V. This study presents the characterization of microstructure and mechanical hardness of as-cast Ti-6Al-7Nb and after solution treatment. The Ti-6Al-7Nb alloy was fabricated by the centrifugal casting method. Solution treatment was carried out at 970°C for 1 hour, followed by oil quenching, and consecutively an aging treatment was applied at 500°C for 8 hours. The microstructure was studied by an optical microscope. The mechanical hardness was measured by microhardness Vickers. The results show that the mechanical hardness of the Ti-6Al-7Nb decreased from 396.2 to 377.2 HV as a result of the solution treatment. Reduction in the hardness was attributed to the phase transformation of α to the β phase during the solution treatment. The XRD analysis showed a reduction in the intensity of α phases at the (011), (012), and (020) planes in the alloy after the solution treatment. The results indicated that the microstructure and mechanical hardness of Ti-6Al7-Nb alloy were affected by the solution treatment.