Effects of severe plastic deformation on microstructure, strength and other technological properties of commercial purity titanium used for implants

Abstract

Commercially pure Ti and the Ti6Al4V alloy have been used as implant materials because of their excellent propertied in that context. However, the former material has low strength when compared to the alloy, which in its turn contains two potentially cytotoxic elements, that is, Al and V. On the other hand, it has been demonstrated that severe plastic deformation or SPD causes a drastic increase in tensile strength by reducing the grain size to nanometric or submicrometric dimensions. This mechanism can be exploited to upgrade the tensile strength of commercially pure Ti, thus creating an alternative to the Ti64 alloy.The present study intends to apply one of the many SPD methods, viz., the ECAP technology (Equal Channel Angular Pressing) combined with cold rolling, to increase the tensile strength of Ti Grade 2 up to H 1000 MPa, while still maintaining a reasonable ductility. Special attention will be given to determine the pressing temperature and minimum deformation level, which are important process parameters in the production of a homogeneous and small grain size. Transmission electron microscopy, Electron Backscattered Diffraction, microhardness measurements and tensile/compression test will be used to characterize microstructural evolution, strength, work hardening behavior and strain rate sensitivity. Finally, the influence of ECAP - deformation on two technological properties: corrosion and machinability will be assessed by standard tests. The results of this study can contribute to a better knowledge of commercial Ti as a biological implant material, thus opening the way to consideration of its use as a replacement of the more expensive and potentially dangerous Ti64 alloy. (AU)