IRREVERSIBLE-PROCESSES DURING MARTENSITIC-TRANSFORMATION IN ZR-BASED SHAPE-MEMORY ALLOYS

The purpose of this paper is to explain the thermodynamical and shape memory behaviour in comparison with structural parameters for Zr-based intermetallics - a new class of potential shape memory alloys (SMA) f or high-temperature applications [1]. Electrical resistivity, structur al, shape memory and calorimetric measurements were carried out for th e Zr2CuNi - Zr2CuCo quasibinary cross-section. It was shown that the m artensitic transformation (MT) of the high -temperature B2 phase resul ted in the simultaneous formation of the two martensitic phases belong ing to the P2(1)/m (B19' type) and Cm space groups in the case of Zr2C uNi similar to ZrCu [2]. Co for Ni substitution causes the changes in the martensite volume fractions up to formation of only B19' type mart ensite in Zr2CuCo compound without significant changes in lattice para meters for both martensites. Such substitution also decreases generall y the transformation heats and energy dissipated during the full cycle of MT. The non-thermoelastic behaviour that was observed in [1] for Z r2CuNi changes to a thermoelastic one in the case of MT in Zr2CuCo. Sh ape memory effect (SME) is nearly complete for alloys with high Ni con tent (not less than 85% of shape recovery ratio (K-sme)). It becomes c omplete at Co additions. The effect of the interaction between two mar tensites on the non-thermoelastic MT behaviour and SME in Zr-based int ermetallics is discussed in the present paper.