Enhancement of Shape Memory Properties through Precipitation Hardening in a Ti-Rich Ti-Ni-Pd High Temperature Shape Memory Alloy

摘要

Effects of aging on martensitic transformation temperature, microstructure and shape memory characteristics were investigated for Ti50Ni20Pd30 and Ti52Ni18Pd30 alloys. There was no significant change in the microstructure and transformation temperature by aging, irrespective of aging temperature, in case of the Ti50Ni20Pd30 alloy. On the other hand, fine Ti2Pd type precipitates were formed upon aging in the Ti52Ni18Pd30 alloy within the aging temperature range of 673-1073 K. The transformation temperature of the Ti52Ni18Pd30 alloy was sensitively dependent on the aging temperature. The Ti2Pd type nanoscaled precipitates were found to be very effective in enhancing the high temperature dimensional stability during shape memory cycling. Excellent shape memory properties with a large recovery strain and a small plastic strain even at 500 MPa were observed in the Ti52Ni18Pd30 alloy solution treated and aged at lower temperatures of 673 and 773 K owing to the formation of fine and dense Ti2Pd type precipitates.