EFFECT OF CHI-PHASE PRECIPITATION ON ELASTIC-MODULUS OF CU-AL-NI-(TI)-(MN) SHAPE-MEMORY ALLOYS

Cu-Al-Ni shape memory alloys present a minimum in their elastic modulu s during the martensitic transformation, and the values in both the ma rtensite and high temperature beta-phase, follow the same trend. The a ddition of Ti, as grain refiner, produces chi-phase precipitates which substantially modify the elastic modulus profile of the alloy. The el astic modulus values of both martensite and beta-phase increase to a d ifferent level, and no minimum during the transformation is observed. The specific changes in the elastic modulus depend upon the size distr ibution of the chi-phase precipitates, which, in turn, is a function o f the thermomechanical history of the material. In the present article , a dislocation string model is used to qualitatively explain the elas tic modulus profiles, making use of the coherency degree of the precip itates.