BETEROGENEOUS GRAN REFNEMENT OF BOMEDICAL Ti-29N-13Ta-46Zr ALLOY THROUGHHGH-PRESSURE TORSON

The biomedical B-type titanium alloy Ti-29Nb-13Ta-4.6Zr (TNTZ) exhibits non-toxicity and a low Young s modulus that is similar to that of bone. This alloy has a low Young s modulus because it contains a metastable B phase. Strengthening due to grain refinement tends to provide high mechanical strength while keeping the Young s modulus low because it maintains the original B phase. In this case, severe plastic deformation such as high-pressure torsion (HPT) is a potential treatment to obtain these properties simultaneously. Thus, in this study, the effect of HPT on the microstructure and hardness of TNTZ was systematically investigated. On the cross sections of TNTZ subjected to HPT, a heterogeneous microstructure consisting of a matrix and an unetched band not corroded by an etching solution were observed. Both the matrix and the unetched band comprise a single B phase with submicron-sized grains, but their grain geometries differed: equiaxed grains and elongated grains are observed in the matrix and the unetched band, respectively. The hardness distribution in the cross section of TNTZ subjected to HPT is also heterogeneous; the hardness is higher in the matrix than that in the unetched band when the number of HPT rotations is small.

Keywords:

Biomaterial , B-type titanium alloy , Severe plastic deformation , Grain refinement