Complex multi-step martensitic twinning process during plastic deformation of the superelastic Ti-20Zr-3Mo-3Sn alloy

The Ti-20Zr-3Mo-3Sn (at.%) alloy is investigated before and after deformation by conventional and cyclic tensile tests, electron back-scattered diffraction (EBSD), in situ synchrotron X-ray diffraction (SXRD) and transmission electron microscopy (TEM). On one hand, the maximum recovery strain of 3.3% is obtained, which is attributed to the favorable {111} < 101 >(beta) texture of beta phase after short solution treatment. On the other hand, plastic deformation mechanisms are studied from specimens strained to 5% and 8%. The reversible stress-induced martensitic (SIM) alpha transformation is preliminary detected by SXRD during loading and after unloading in both specimens. Then, the deformation microstructures are further inves-tigated in details by TEM. At 5% of strain, primary alpha deformation bands are observed with an abnormal orientation relationship (OR) with beta phase. From crystallographic reconstruction, this OR is shown to be due to {130}< 310 >(alpha) twinning followed by {111}alpha?? type I reorientation twinning during loading. At 8% of strain, a complex hierarchical microstructure composed of primary and secondary alpha bands is observed, which corresponds to residual primary {130}< 310 >(alpha) twins with secondary {130}< 310 >(alpha) twins occur-ring after {111}alpha?? reorientation twinning of primary {130}< 310 >(alpha) twins. The sequence of plastic defor-mation is then composed of primary {130}< 310 >(alpha) twinning, followed by {111}(alpha)?? reorientation twinning and finally secondary {130}< 310 >(alpha) twinning. A thin layer of omega phase is also observed at the beta/alpha inter -phase boundary. Occurrence of this unprecedented complex multi-step martensitic twinning process is rationalized by means of Schmid factor analysis and transformation strain calculations. (C)2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

The Ti-20Zr-3Mo-3Sn alloy was investigated before and after deformation, and it was found that a large recovery strain could be obtained after short solution treatment. The reversible stress-induced martensitic transformation was detected during loading and unloading, and the deformation microstructures were studied in detail. A complex multi-step martensitic twinning process was observed, and the occurrence of this process was rationalized through analysis and calculations.