The characteristics of precipitation hardening and the shape memory effect in aged Ti50.6Ni39.4Cu9.8Si0.2 shape memory ribbons

As-spun Ti50.6Ni39.4Cu9.8Si0.2 shape memory ribbon fabricated by the melt-spinning technique is found to be partially amorphous. The ribbon is crystallized at 550 °C for different aging times. Nanoindentation testing revealed the hardness of the amorphous region to be about 7.8 GPa, but that of the crystalline region is 3.1 GPa. The average hardness of the aged ribbon is 3.4 GPa at 550 °C×15 min aging and then decreases continuously. In 550 °C×1 h-aged ribbon, TEM observations show that GP zones and nanoscale Ti2Ni formed in the primary grain, and only GP zones are observed in the crystallized equiaxed grain. Both of these nanoscale precipitates strengthen the matrix and cause precipitation hardening. The 550 °C×15 min-aged ribbon exhibits an excellent shape memory effect, with recoverable strain of 6.2%. The recoverable strain of the ribbon gradually decreases with increasing aging time; however, it still shows recoverable strain of >4% with irreversible strain of <0.3% in each tested ribbon. Experimental results show that Ti50.6Ni39.4Cu9.8Si0.2 ribbon exhibits less thermal hysteresis than TiNi binary ribbons. Also, it has better SME performance and is less brittle than Ti50Ni25Cu25 ribbons in the early-aging stage.