Study on High Strength Ti-Al-V Alloy at Cryogenic Temperature

P K Mandal; Alex Joseph; Colin Siby; Jithin Devasia

Abstract

The α+β type high strength titanium alloy is usually used as a structural biomaterial for the manufacturing of orthopaedic prostheses as well as surgical and dental implants. The Ti-Al-V alloy had been deliberately solution treated at 860°C for 1 h (subsequently quenched in variable mediums) just below the β transus but within the α+β region to avoid grain coarsening for single β region as well as accomplish optimum balance properties of ductility and strength. It was found that during solution treatment plus subsequently age hardening treatment at 500°C for 5 h (STA) decomposition taking place from low modulus martensite and retained β phases into high modulus α phases (70–75 GPa). Meanwhile, the aged titanium alloy was examined through light optical microscopy, SEM with EDS analysis, Vicker’s hardness measurements, tensile properties and SEM with EDS fractography analysis. The better tensile properties have been achieved after ageing treatment in CT (i.e., specially quenching in water and cryogenic temperature (CT) after solution treatment) such as hardness of 408.8.3±8.3 HV, UTS of 1132 MPa, YS of 746 MPa, El of 3.0%, RA of 4.43%, respectively. The strength can be attributed to the fine precipitates of α phase as results of decomposition of martensite, carbo-nitride and retained β phases. The main reason for better strengthening of the present CT titanium alloy is the transformation of metastable β phase into needle shape α' martensite which results in reduction of β phases in the microstructure after ageing treatment.