GRAIN BOUNDARY ENGINEERING OF POLYCRYSTALLINE SHAPE MEMORY ALLOYS BY PHASE MANIPULATION FOR ENHANCED MECHANICAL DUCTILITY AND APPLICATION FATIGUE LIFE

摘要

Provided is a method of making a polycrystalline shape memory alloy (SMA) by forming an alloy with grains and boundaries between them, exposing the alloy to a two-phase temperature range at which a two-phase equilibrium is achieved in the alloy, converting grains to an austenite phase, and precipitating a face-centered-cubic crystal structure solid solution phase at grain boundaries, then quenching the alloy. Also provided is a polycrystalline SMA with a dual-phase microstructure having grains mostly in an austenite phase, a martensite phase, or in transition between an austenite phase and a martensite phase and grain boundaries containing a face-centered-cubic crystal structure solid solution phase.