Effects of thermal cycling on the martensitic transformation in two-phase α/β brasses

Abstract

The effects of thermal cycling between the parent and martensite phases of two-phase α/β CuZn alloys have been studied by electrical resistance-temperature measurements, optical microscopy, and transmission electron microscopy (TEM). The martensite start (Ms) temperature is dominated primarily by the composition of the β phase but increases substantially between the first and second cycles because of deformation of the α particles and a resultant change in the internal strain fields of the system. With increasing thermal cycling, the Ms temperature increases slightly and eventually becomes constant. However, the transformation hysteresis becomes smaller, and more perfect thermoelastic behavior is found. The number of vestigial deformation markings in the β phase is increased by thermal cycling and becomes more distinct; the dislocation density in the β phase is also increased and features a more crystallographic arrangement. The vestigial deformation of the β phase is instrumental in subsequent martensite nucleation and in creating a martensite microstructural memory.