Orthogonal shear process in Ni-Mn-Sn single crystal

Abstract

A coordinate change of conjugation twin boundaries in Ni-Mn-Sn single crystals is studied with scanning electron microscopy. During mechanical training, the so-called orthogonal shear process initiates variant reorientation leading to the replacement of the main with conjugation type I twin boundaries. The experimental data demonstrate that highly organized redistribution of adjacent variants, in the neighboring areas, is then critical for the removal of conjugation boundaries by coordinated secondary twinning. In addition, a more complex variant reorientation mechanism is uncovered and it is found to allow for transitioning between non-conjugate twin systems. The proposed mechanism appears consistent with the orientation relationship between austenite and martensite, which is controlled by a shear deformation and martensite crystallography leading to an equal distribution of martensitic variants. This contribution complements the existing theory of martensite crystallography providing direct evidence for the general nature of the orthogonal shear process as a first step in variant reorganization during mechanical training of martensite.