Mechanical behavior and phase stability of NiAl-based shape memory alloys

Abstract

NiAJ-based shape memory alloys (SMAs) can be made ductile by alloying with 100-300 wppm B and 14-20 at.% Fe. The addition of Fe has the undesirable effect that it lowers the temperature (A,,) of the martensite-*austenite phase transformation. Fortunately, however, A,, can be raised by lowering the '_uivalcm" amount of AI in the alloy. In this way a high A,, temperature of-I_PC has been obtained without sacrificing ductility. Furthermore, a recoverable strain of 0.7% has b_n obtained in a Ni-AI-F¢ alloy with A_ temperature of 140°C. Iron additions do not suppress the aging-induced ¢mbritflement that occurs in NLM allo_ts at 300-5000C as a result of NisAl 3 precipitation. Manganese additions (up m 10 at.%) have the effect of lowering Am,,degrading hot workability, and decreasing room-tempemm_ ductility.