Microstructural evolution of Ti-6Al-7Nb alloy during high pressure torsion

Abstract

Ti-6Al-7Nb alloys are being evaluated for biomedical applications, in substitution of the more conventional Ti-6Al-7V. Both types of alloys present a microstructure containing the α and the β phases, which result in good compromise for mechanical applications. In the present work Ti-6Al-7Nb alloys were processed by High Pressure Torsion (HPT), varying the number of revolutions and thus the total imposed strain. X-Ray Diffraction (XRD) results revealed the formation of different crystallographic textures in samples subjected to HPT. Microhardness distribution, across the diameters of the disks, is rather homogeneous for all samples, with higher values for those subjected to 03 and 05 turns. Transmission electron microscopy (TEM) micrographs have showed that an ultra-fine grained microstructure was obtained in all the samples.

Superplasticity in the Ti–6Al–7Nb alloy processed by high-pressure torsion

“…The grain size is finer after processing by HPT and it is smaller with increasing number of revolutions. The grain size of ~100 nm obtained after HPT processing through N = 5 is smaller than the grain size of 200 nm, obtained after processing by ECAP [13]; however, this result is consistent with the value of 97 nm reported earlier using HPT [14]. The difference in the grain size may be due to the difference in the imposed strain, which is higher in the HPT processing.…”

Texture evolution in high-pressure torsion processing

“…It is noted that no information is available concerning the evolution of the texture as a function of the number of HPT turns in Tibased alloys. However, based on the X-ray diffraction patterns for HPT processed Ti-6Al-7Nb alloy a basal fiber may form after N = 1 and 3 turns and a decrease of the intensity of the (0002) peak is evident after N = 5 turns indicating a change in the texture [219].…”

Effects of High-Pressure Torsion on Mechanical Properties of Biocompatible Ti–6Al–7Nb Alloy

“…Pinheiro et al reported that, when the as-cast Ti6Al7Nb alloy was subjected to HPT, the grain size was reduced to 97 nm after 3 revolutions and 107 nm after 5 revolutions. 44) The Vickers hardness increased from 190 HV to approximately 340 HV by applying HPT under a pressure of 5 GPa. It was thus concluded that HPT could enable the grain refinement of the Ti6Al7Nb alloy.…”