Accommodation mechanisms in strain-transformable titanium alloys

TL;DR

This paper reports the design and analysis of a novel strain-transformable titanium alloy that exhibits high ductility and stable work-hardening, with deformation mechanisms involving twinning and stress-induced martensite acting as accommodation processes.

Contribution

It introduces a new Ti-alloy positioned at the boundary between TRIP and TWIP regimes, demonstrating its deformation behavior and underlying mechanisms.

Findings

Large ductility with stable work-hardening observed.

Deformation primarily via {332}<113> twins without primary martensite.

Stress-induced martensite acts as an accommodation mechanism.

Abstract

A new $\beta$-metastable Ti-alloy is designed with the aim to obtain a TWIP alloy but positioned at the limit between the TRIP/TWIP and the TWIP dominated regime. The designed alloy exhibits a large ductility combined with an elevated and stable work-hardening rate. Deformation occurring by formation and multiplication of {332}<113> twins is evidenced and followed by in-situ electron microscopy, and no primary stress induced martensite is observed. Since microstructural investigations of the deformation mechanisms show a highly heterogeneous deformation, the reason of the large ductility is then investigated. The spatial strain distribution is characterized by micro-scale digital image correlation, and the regions highly deformed are found to stand at the crossover between twins, or at the intersection between deformation twins and grain boundaries. Detailed electron back-scattered imaging in such regions of interest finally allowed to evidence the formation of thin needles of stress induced martensite. The latter is thus interpreted as an accommodation mechanism, relaxing the local high strain fields, which ensures a large and stable plastic deformation of this newly designed Ti-alloy.