EMBEDDED-ATOM METHOD STUDY OF THE EFFECT OF THE ORDER DEGREE ON THE LATTICE-PARAMETERS OF CU-BASED SHAPE-MEMORY ALLOYS

Using the embedded-atom method, the variation in the total energies an d lattice parameters with the degree of long-range order has been calc ulated for the parent and 18R1 martensite phases for several Cu-Zn-Al and Cu-Al-Ni shape memory alloys. It was found that the bond angle phi , i.e. the angle between lines connecting the nearest neighbours in th e basal plane of the martensite, increases with increase in degree S(B 2) of B2-type order for both Cu-Zn-Al and Cu-Al-Ni alloys. When the de gree S(L2) of L2(1)-type order increases, the bond angle phi increases for the Cu-Zn-Al shape memory alloys, but it decreases for the Cu-Al- Ni shape memory alloys. This result agrees well with experiment.