Self-accommodation of B19′ martensite in Ti-Ni shape memory alloys - Part II. Characteristic interface structures between habit plane variants

Four characteristic interface microstructures between habit plane variants (HPVs) in the self-accommodation morphologies of B19' martensite in Ti-Ni alloys have been investigated by scanning transmission electron microscopy (STEM). The straight interface of a {(1) over bar(1) over bar1}(B19') type I twin is present at interface I. The relaxation of the transformation strain at interface II is achieved by a volume reduction of the minor correspondence variants (CVs) in the relevant habit plane variants (HPVs). The relaxation of the transformation strain at interface III is mainly due to the formation of a {(1) over bar(1) over bar1}(B19') type I twin between the two major CVs. Subsequently, local strain around the tips of the minor CVs perpendicular to the interface is released by the formation of micro-twins with the < 011 >(B19') type II and/or {(1) over bar(1) over bar1}(B19') type I relation. The major and minor CVs in each HPV are alternately connected through fine variants with the {(1) over bar(1) over bar1}(B19') type I twin relation parallel to interface IV. The results are compared with macroscopic observations and the predictions of PTMC analysis.