On the martensitic transformation temperature and its stress dependence in Cu-Zn and Cu-Zn-Al single crystals

Publisher Website
Google Scholar
Abstract
The critical stress to induce martensite in Cu-Zn and Cu-Zn-Al single crystals has been determined down to 80 K. It has been found that the stress increases linearly with increasing temperature. From this result it is deduced that the higher vibrational entropy of the beta -phase compared with the martensite is due solely to the soft transverse ( zeta zeta 0) phonon modes, the other modes remaining largely unaffected by the transformation. This result is consistent with the predictions of Zener on the stability of beta -phases in the noble-metal alloys. The linearity in the temperature dependence of the critical stress has been used to obtain transformation temperatures by a linear extrapolation to zero stress. The results for alloys with Zn concentrations between 40 and 45 at.% Zn can be expressed as Ms (K)=2686-64 CZn. This dependence is different from what has been reported in the literature before. Finally, the influences of previous plastic deformation in the beta -phase and of a stress-induced transformation of the martensite to the FCT phase are considered.