STRAIN INDUCED PHASE TRANSFORMATION IN Ti-15Mo β ALLOY

^a School of Engineering Technology, Purdue University, West Lafayette, IN47906, USA
^b Medtronic Neuromodulation, 7000 Central Avenue NE, Minneapolis, MN55432 USA

Abstract

β-Ti alloys have been chosen for biomedical applications attributed to a combination of high strength, high fatigue resistance, good corrosion resistance and more importantly low modulus closer than other metallic materials for implants and osseointegrated prosthesis to the cortical elastic modulus (4-30 GPa). However, the phase constituents and phase transformation are still under dispute. A Ti-15Mo alloy after severe cold plastic deformation is studied to reveal the phases and phase transformation by TEM techniques. Athermal ω phase was observed in all samples evidencing the high stability of ω phase compared to β phase. However, the β to ω transformation does not proceed to a completion in heat treatment. Strain induced phase transformation happens in cold-draw wires through a coordinated shuffle of atoms along the {2 1 1}planes of β phase leading to the reduction on the <1 1 1> directions. The atomic level of shear causes the transformation of β to ω. The transformation of β to athermal ω under a train is not in a stable state but having a variable crystal structure between β and ω.