Impact Toughness of Ultrafine-Grained Commercially Pure Titanium for Medical Application

Abstract

This study aims at achieving the best combination of strength, ductility, and impact toughness in ultrafine-grained (UFG) Ti Grade 4 produced by equal-channel angular pressing via Conform scheme (ECAP-C) with subsequent cold drawing. UFG structures with various parameters (e.g., size and shape of grains, dislocation density, conditions of boundaries) are formed by varying the treatment procedures (deformation temperature and speed at drawing, annealing temperature). The tensile and impact toughness tests were performed on samples with a V-shaped notch and different structures of commercially pure Ti Grade 4 in the coarse-grained and UFG states. The results demonstrated that grain refinement, higher dislocation density, and their elongated shape were obtained as a result of drawing at 200 degrees C, which led to a decrease in both the uniform elongation at tension and the impact toughness of Ti Grade 4. Short-term annealing at 400-450 degrees C could improve the impact toughness of UFG Ti with a non-significant decrease in strength. This short-term annealing contributes to the dislocation density decrease without considerable grain growth as a result of the recovery and redistribution of dislocations. The dependence of impact toughness on the strain hardening ability of UFG Ti was discussed.