Martensitic transformation in Zr-Ti alloys

Abstract

Martensitic transformation in a series of Zr-Ti alloys has been studied by transmission electron microscopy. A transition in morphology and substructure was observed with increasing additions of titanium. The 5 wt pct Ti alloy was found to be predominantly dislocated lath martensite while the 10 wt pct Ti alloy showed mainly a twinned plate morphology. Twins within the martensite plates could be classified into two categories, namely, thick {1011} twins and thin twins mainly on {1011} planes and, to a lesser extent, on {1122} and {1121} planes. In the case of the thick {1011} twins, the specific variant of the twin plane was always found to correspond to a plane of the {110} bcc type, which is a mirror plane in the parent bcc crystal. When the specific variant of the composition plane was not parallel to a mirror plane, the twins were observed to be very thin. Evidence of slip within individual twin bands pointed to the operation of a multiple shear inhomogeneous deformation {1011}. Observations concerning deformation twins due to impingement effect are also discussed in this paper.