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].…”

The Ultrafine-Grained Titanium and Biomedical Titanium Alloys Processed by Severe Plastic Deformation (SPD)

“…Pinheiro et al [32] reported that HPT proved to be an effective way to produce the UFG Ti-6Al-7Nb alloy, manifested by the increase of micro hardness 78.7% after 5 turns. Meanwhile, the dynamic recovery of the deformed microstructure reached a quasi-equilibrium state, indicating that saturation of the grain refinement was attained and no new defects were formed with higher plastic strain.…”