Cold Swaging and Recrystallization Annealing of Ti-Nb-Ta-Zr-O Alloy - Microstructure, Texture and Microhardness Evolution

Abstract

Metastable β-Ti alloy Ti-35.3Nb-7.3Zr-5.7Ta-0.7O (wt. %) shows properties desirable for use as an implant material. However, very large grains (with the size of 0.5 – 3 mm) negatively affect the strength and fatigue resistance. Combination of cold-swaging and recrystallization annealing is used to refine the microstructure. Microstructure after cold swaging and after annealing is studied using scanning electron microscope by electron back-scatter diffraction measurements. Grain size and texture is determined and homogeneity of deformation inside the grains is discussed. Microhardness maps are measured in the cold-swaged samples. It is found that microhardness and thus also the deformation is higher in the center of each rod however the grains retain their original size. Annealing leads to recrystallization that is complete or nearly complete at the temperatures of 1000°C and more. Annealing at 1000°C for 15 min yields grain size of around 100 μm. This grain size is believed to increase the fatigue performance to satisfactory values.

Phase Transformations upon Ageing in Ti15Mo Alloy Subjected to Two Different Deformation Methods

“…In the rudimentary stage of the HPT deformation, a twinning process takes place, which is followed by significant grain refinement [31,33,34]. In contrast, deformation using RS creates shear bands with a high density of lattice defects and refined grains with an elongated character, as also reported in studies [35][36][37][38]. The shear bands are caused by the dislocation slip during RS, while the elongated character of the grains is the result of the combination of a dislocation slip and a grain boundary slip [37].…”