Coupled shear and shuffle modes during twin growth in B2-NiTi

Deformation twinning of B2 austenitic phase in NiTi has not been understood despite its significance. A number of experimental observations have been made, but these alone cannot explain the complex shears and shuffles that produce the twin. We propose that twinning can occur via ((2) over bar 11)[(1) over bar(1) over bar(1) over bar] shear and the proposed shuffle differs from previous work and is parallel to the twinning shear. We established a twin energy barrier which is lower compared the previously proposed twinning modes, and has a magnitude of 79 mJ/m(2). Hydrostatic pressure is found to alter this energy barrier and the coupling of shear and shuffle mechanism. (C) 2011 American Institute of Physics. [doi:10.1063/1.3596458]