Pseudoelastic effects in CuZn single crystals

Abstract

Mechanical properties associated with pseudoelastic phenomena in CuZn single crystals have been studied and characterized. As a result it is possible to clarify superelastic properties and to report on a new rubber-like behavior. Two-surface analysis at a range of temperatures above M s demonstrated that the habit plane and shape strain direction of the stress-induced martensitic variant were those associated with the lowest Schmid factor of the 24 possible variants. The magnitudes of the measured strains were identical to the resolved theoretical values calculated from the phenomenological theory. The influence of temperature, strain rate, and the amount of superelastic cycling above M s was observed. The onset of ‘advanced deformation’ (by either the nucleation of reversible α s martensite or plastic flow) caused modification in the pseudoelastic loops of the stress-strain curves. ‘Training’ of specimens above M s caused the nucleation of the same variant when cooling to near M s . However, for certain orientations of the stress-induced martensite (SIM) single crystals further cooling caused a subsequent transformation of the SIM into a (2, 0, 10) 9R twin as the temperature approached M ƒ . The twinned single crystal of martensite was observed to behave in a rubber-like fashion on load cycling below M ƒ . The rubber-like behavior is due to twin boundary movement of the trained SIM variant and its (2, 0, 10) 9R twin. Magnitudes of the rubber-like strain have been measured and compared to the predicted theoretical values.