Revealing the mode and strain of reversible twinning in B19 ' martensite by in situ synchrotron X-ray diffraction

The challenges in the identification of reversible twinning modes and in the measurement of reversible twinning strain impede the thorough understanding of twinning induced elasticity (TIE). In this report, we exploited the mode and strain of reversible twinning in B19 ' martensite in a Nb-nanowire/NiTiFe-matrix alloy. TIE strain up to 5.1% was achieved by pre-deforming the alloy up to an applied strain of 55.7%. In situ synchrotron X-ray diffraction (XRD) results show that B19 ' ( 20 1 over bar ) and ( 1 over bar 11 ) twins were in-duced by pre-deformation. More importantly, a large portion of these twins were found reversible for the first time. It is suggested that the reversibility is probably facilitated by the internal stresses gener-ated during large plastic deformation. Furthermore, the reversible twinning strain was measured using XRD based on a 'lattice strain matching' concept such that the contribution of reversible twinning to TIE was clarified. The measured twinning strain was compared with the calculated strain based on twinning crystallography. (c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.