ELASTIC PROPERTIES OF B2-NITI AND B2-PDTI

Elastic constants of the high-temperature phases of the shape-memory alloys NiTi and PdTi are determined by means of full-potential linearized augmented-plane-wave total-energy calculations. Thereby, insight into the driving mechanism of the martensitic transformation of these alloys can be obtained. In the case of NiTi, the c and c44 moduli are found to be low and to decrease with rising pressure. We find that the (parent) PdTi phase is metastable with respect to tetragonal deformations. From these data, we can explain the different transformation behavior of the two alloys. In the case of PdTi, the Ti-Ti bonding seems to be responsible for the formation of the martensitic phases. Experimental data, if available, are found to be in good agreement with the results of our calculations. © 1994 The American Physical Society.