Transformation induced toughening in a Ni-Ti 52 shape memory alloy

In this work the mechanical behavior of a Ti-rich Ni-Ti shape memory alloy was investigated. In particular, it was found that this alloy contains a re latively high volume fraction of brittle precipitates (4 vol.%). Neverthele ss, the alloy exhibits unusually elevated plasticity and work hardening pro perties. These properties cannot be simply described in terms of dislocatio n slip mechanisms alone. The experimental outcome indicates that high stres s build-ups due to plastic incompatibilities can be relieved through revers ion of martensite into the austenitic B2 phase. It was found that regions o f highly localized stress concentrations such as crack tips developed a fin e-grained structure upon crack advance. The "trail" of fine martensite grai ns found on the fractured surfaces can be satisfactorily explained by the s tress-induced reversed transformation. (C) 2001 Elsevier Science B.V. All r ights reserved.