Elastic constant softening and martensite nucleation in a CuZnAl single crystal

The internal friction (IF) and Youngʹs modulus (E) of a Ni50.8Ti49.2 is affected by thermal cycling. With increasing the number n of thermal cycles, the IF peak PAM (PMA) occurring at the austenite/martensite transition temperature decreases to disappear almost completely. Meanwhile the associated E(T) minimum at the beginning (n<250) deepens and then becomes progressively shallower and wider (3×1033×103, the direct transformation is to some extent hindered by the dislocation network introduced by thermal cycling. A not thermally activated IF peak PTWM, which is believed to be due to stress-assisted motions of (001) compound twin boundaries in the homogeneous martensite state, grows with increasing n.