High strain rate shear deformation and fracture behaviour of biomedical titanium alloy

Abstract

The rate and temperature dependent shear deformation behaviour of biomedical titanium alloy (Ti–15Mo–5Zr–3Al) is investigated using a torsional split Hopkinson pressure bar at strain rates ranging from 1·2 × 10³ to 2·8 × 10³ s^–1 and temperatures of –150, 25 and 300°C. It is found that both the strain rate and the temperature have a significant effect on the high strain rate shear properties and fracture characteristics of the alloy. As the strain rate is increased or the temperature is reduced, the flow stress, workhardening rate, strain rate and temperature sensitivity increase, but the activation volume and activation energy decrease. The fracture strain increases with both increasing strain rate and increasing temperature. The shear flow behaviour of the Ti–15Mo–5Zr–3Al specimens is accurately described by the Kobayashi–Dodd constitutive equation. Metallographic observations reveal that the failure of the present Ti–15Mo–5Zr–3Al alloy is dominated by intensive localised shearing. Moreover, the SEM fractographs show that the fracture surfaces are characterised by a dimple-like structure. The dimple density increases with an increasing strain rate or temperature. By contrast, the dimple size reduces at higher strain rates and temperatures and gives rise to a significant improvement in the fracture resistance.