Microstructural characterization of Ti-6Al-7Nb alloy after severe plastic deformation

Abstract

The ASTM F1295/Ti-6Al-7Nb alloy present mechanical properties and biocompatibility very attractive for application in medical and dental implants. In this context, processing of these Ti-based alloys by severe plastic deformation (SPD) has been extensively reported recently. However, the mechanical properties of equal channel angular pressed (ECAP) ASTM F1295 alloy are still a matter of research. In the present study, Ti-6Al-7Nb samples were processed by ECAP following thermomechanical processing which effects on the microstructure of Ti-6Al-7Nb alloy were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The analyses have shown that the microstructure was composed by ultrafine grains (UFG) with sizes ranging from 200 to 400 nm. Ring-type selected area electron diffraction patterns (SAEDP) suggested the co-existence of low-and high-angle grain boundaries. Some regions of the samples have presented evidences of the presence of grains with unfavorable orientation to the plastic deformation. These grains can act as rigid bodies and concentrate the deformation in its surrounding areas, as an "open-die grain" mechanism. Such deformation mechanism could be attributed to the differences in the plastic behavior between the alpha and beta titanium phases.

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.…”

Comparison between the machinability of different titanium alloys (Ti–6Al–4V and Ti–6Al–7Nb) employing the multi-objective optimization

“…Still, according to Gallego et al [5], an alloy with similar properties, containing niobium instead of vanadium as stabilizing element of the β phase, was developed. Niobium has excellent biocompatibility and, when associated with aluminium, accounts for most of the solid strengthening of the alloy [6].…”

Study on Corrosion Behavior of Ultrafine-Grained Ti-6Al-7Nb Fabricated by Equal Channel Angular Pressing

“…Recently, ultrafine-grained (UFG) and nanocrystalline (NC) materials processed by severe plastic deformation (SPD) have been widely investigated and found to have unique physical and chemical properties [11][12][13]. Enhanced mechanical behavior and biocompatibility of UFG/NC Ti-6Al-7Nb alloy were acquired after the SPD process [14][15][16][17][18][19]. For instance, Polyakova et al [9] revealed that the tensile strength of the UFG Ti-6Al-7Nb alloy with grain size of 330 nm increased to 1210 MPa after equal channel angular pressing (ECAP), which was 20% higher than observed in coarse-grained (CG) counterparts.…”