Acoustic emission during martensitic transformation in Cu-Mn-Al alloy

Abstract

Simultaneous measurements of acoustic emission and electric resistivity was carried out during martensitic transformation in Cu-11.89 wt pct Al-5.75 wt pct Mn alloy. Acoustic emission generated during nucleation and annihilation of thin martensite plate have low m value than that during the frictional interaction during the propagation of the martensite/austenite interfaces, then higher fraction of higher peak ampilitude AE events released during the nucleation and annihilation is arisen from the shorter rise time of the AE events. The elastic strain energy stored in martensite is released during the reverse transformation, during which the propagating interface have to overcome higher energetic barrier of structural obstacles, producing more abrupt change in elastic strain and releasing more energetic high amplitude as well as greater number of AE events during the reverse transformation. The temperature shift of AE starting/finishing in relation to that of $M_s/M_f$ and $A_s/A_f$ during the forward and reverse transformation, respectively, is caused by the difference in physical contents to be measured. The effects of thermal cycling and heating/cooling rate during martensitic transformation were observed by the electric resistance vs temperature hysteresis. The broadening of $\mid{M_s-M_f}\mid$ and $\mid{A_s-A_f}\mid$ with an increase of heating/cooling rate indicates the more elastic strain energy stored in martensite and stabilization of martensite during the forward and reverse transformation, respectively. The more reduction of the effective transformed volume increased with an increase of thermal cycling and a decrease of heating/cooling rate, and it may be arisen from the more production of the precipitation or stabilization of the martensite. In addition, the acoustic emission was studied during the thermal cycling. The decrease of the accumulated AE events energy per thermal cycling with an increase of thermal cycling may be condidered to be caused b...