Mechanism of deformation and crystal lattice reorientation in strain localization bands and deformation twins of the B2 phase of titanium nickelide

Optical metallography and transmission electron microscopy were used to investigate the formation and microstructure of strain localization bands and deformation twins in single crystals of a TiNi alloy deformed by rolling. On the basis of these investigations, with the use of the theory of martensitic transformations based oil the concept of cooperative thermal vibrations of coherent objects (close-packed planes) in crystals, a new mechanism of twinning in these alloys is suggested, namely, through the forward plus reverse (B2 --> B19 --> B2) martensitic transformations with the reverse transformation developing via an alternative transformation system. It is shown that using this mechanism one can describe on the same grounds the twinning in the crystal lattice of the B2 phase with twin planes of different ({1 1 2}, {1 1 3}, and {3 3 2}) Miller indices and the formation of strain localization bands with low-angle misorientations. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.