INFLUENCE OF GRAIN-SIZE AND ORDERING DEGREE OF THE PARENT PHASE ON MS IN A CUZNAL ALLOY CONTAINING BORON

The influence of the average grain size and ordering degree of parent phase on the starting temperature of thermoelastic martensitic transformation in a Cu-25. 62 Zn-3. 97 Al-0. 0018 B (wt%) shape memory alloy was studied. Based on the thermodynamics of phase transformation, a linear relationship between the starting temperature of martensitic transformation and the reciprocal of the square root of grain size is obtained, i. e. M//s temperature decreases with increasing grain size. Application of L. D. Landau's theory gives a quantitative relationship between M//s temperature and the ordering parameter of the parent phase which is confirmed by the results of X-ray diffraction and electric resistance measurement. The activation energy of the ordering process is calculated to be 46 kJ/mol.