Abstract: The effect of grain size and ordering of the parent phase on the critical points of thermoelastic martensitic transformation in Cu-25.62 Zn-3.97 Al-0.0018 B(wt-%)shape memory alloy has been investigated.Based on the thermodynamics of phase transformation,a linear rela- tionship between the starting temperature of martensitic transformation and the reciprocal of the square root of grain size is obtained,i.e.M_s temperature rises with increasing grain size. It shows a good agreement with the results of electric resistance measurement.Applying the Landau's theory,a quantitative relationship between M_s and the ordering parameter of the parent phase is set up,which is well confirmed by the results of X-ray diffraction and electric resistance measurement.The activation energy of the ordering process in the parent phase of the alloy is calculated to be 46 kJ/mol.

Key words: Cu-Zu-Al, shape memory alloy, thermoelastic martensite, grain size, ordering