Eleventh International Conference on Internal Friction and Ultrasonic Attenuation in Solids
J. Phys. IV France 06 (1996) C8-397-C8-400
Nucleation of Martensite in CuZnAl Alloys as Investigated by Young's Modulus and Acoustic Emission MeasurementsB. Coluzzi, A. Biscarini, S. Piazza and F.M. Mazzolai
Phys. Department, University of Perugia, Perugia, Italy
Young's modulus (E) has been measured during cooling/heating cycles carried out between a fixed upper temperature T2 (T2=340 K) and a gradually decreasing lower temperature T1 (T1 =320, 310, 300, 290, 285, 281 and 279.5 K). The E(T) curves show closed thermal hysteretic loops, which are needle-like for T1> while they assume a downward bent shape for T1<Ms. The occurrence of thermal hysteresis in the cooling/heating E(T) curves is interpreted as evidence of the formation, far above Ms, of static martensite embryos, which are stabilued by preexisting lattice defects. The formation, on cooling, and the delayed disappearance, on heating, of these static embryos is believed to be responsible for the needle shaped E(T) loops. Acoustic emission is found to occur only during the heating stages of partial thermal cycles carried out above Ms, suggesting that only the disappearance of a stabilized embryo is associated with an abrupt release of the stored energy.
© EDP Sciences 1996