STABILITY OF MARTENSITE IN Cu-Zn ALLOYS.

The enthalpy and entropy difference between the beta -phases and martensite has been calculated for Cu-Zn binary and ternary alloys using a description in terms of pairwise chemical interaction energies. It is shown that the concentration dependence of M//s is mainly determined by fourth neighbour pair interactions. This result is also supported by the analysis of the critical stress which is necessary to transform orthorhombic martensite to a fcc-ordered lattice. In contrast to the strong effect which long-range order has on the enthalpy of transformation, the entropy difference has been found to be quite insensitive to order.