Transformation- and stress-temperature behavior of hot-drawn Ni-rich NiTi wire after isochronous aging

Aging temperature in the range of 300-500 degrees C (1 h) strongly affects transformation and mechanical behavior of Ni50.8Ti alloy wire samples obtained as a result of hot drawing at test temperatures of -196 <= T <= 60 degrees C. Isochronous aging of hot-deformed Ni-rich NiTi alloy forms a mixed substructure that consists of grains and subgrains, their average size increases from 0.9 to 3.3 mu m vs temperature growth. In the aging range of 430-500 degrees C the diameter of Ti3Ni4 precipitates grows from 10-20 nm to 0.1-0.2 mu m along the grain/subgrain boundaries. The widest R-s(M) - A(f) temperature range (Delta 76 degrees C) of the reverse MT is revealed after aging at 300 degrees C; the minimal R-s(M) - A(f) temperature range (Delta 10 degrees C) - after aging at 500 degrees C. Aging-induced microstructure strongly affects stress-temperature behavior and Young's modulus: the obtained regularities are associated with contribution of various competing factors.