Heterogeneous grain refinement of biomedical Ti29Nb13Ta4.6Zr alloy through high-pressure torsion

The biomedical -type titanium alloy ti29nb13ta4.6zr (tntz) exhibits non-toxicity and alow young's modulus that is similar to that of bone. this alloy has a low young's modulus because itcontains a metastable phase. strengthening due to grain refinement tends to provide high mechanicalstrength, while keeping the young's modulus low, because it maintains the original phase. in this case,severe plastic deformation, such as high-pressure torsion (hpt), is a potential treatment for obtainingthese properties simultaneously. thus, in this study, the effect of hpt on the microstructure and hardnessof tntz was systematically investigated. on the cross sections of tntz subjected to hpt, heterogeneousmicrostructures, consisting of a matrix and an unetched band not corroded by an etching solution, wereobserved. both the matrix and the unetched band were comprised of a single phase with submicron-sized grains, but their grain geometries differed: equiaxed grains and elongated grains are observed inthe matrix and the unetched band, respectively. the hardness distribution in the cross section of tntzsubjected to hpt is also heterogeneous; the hardness is higher in the matrix than in the unetched band,when the number of hpt rotations is small.