AVALANCHES IN THE GROWTH OF STRESS-INDUCED MARTENSITES

We present an experimental study of phase-transition avalanches during the stress-induced formation of martensite in a Cu-Zn-Al alloy, with particular attention to the effect of cycling. We have analyzed statis tically the amplitudes, durations, and energies of the thermal events accompanying the transition, and found that these magnitudes distribut e according to power laws in the first fifty cycles, within experiment al error, with exponents alpha = 2.3 +/- 0.2, tau = 2.9 +/- 0.7, and e psilon = 1.8 +/- 0.3, respectively. However, the extent of power-law b ehavior is reduced by at least one decade after five hundred transitio n cycles, and the system is seen to become progressively subcritical. We present a method of measuring the distribution of energy barriers e ncountered along the transition, which in our case is found to spread over more than four orders of magnitude. Finally, we have observed tha t repeated cycling leads to a statistical reproducibility of transform ation trajectories, and to the remarkable correlation between the cycl e-to-cycle trajectory fluctuations and the cycle-averaged response fun ction of the system observed recently in magnetic systems [J.S. Urbach , R.C. Madison, and J.T. Markert, Phys. Rev. Lett. 75, 4694 (1995)]. [ S0163-1829(97)09041-3].