Transformational and pseudoelastic characteristics of melt-spun Ti50Ni25Cu25 shape memory ribbon crystallized and aged at a low temperature

The aim of this study is to understand the properties of amorphous Ti50Ni25Cu25 shape memory ribbon crystallized and aged at a temperature lower than its crystallization temperature. The hardness and pseudoelasticity (PE) performance of the ribbons aged at 435 °C, for different intervals, are characterized by nanoindentation. The 435 °C-aged ribbon is fully crystallized and exhibits the lowest hardness value of 5.3 GPa when the aging time reaches 300 min. With increasing aging time to 600 min, the hardness of the ribbon rises to 7.9 GPa due to the strong precipitation hardening effect caused by the fine and dense TiCu precipitates. Additionally, both depth recovery ratio (DRR) and energy recovery ratio (ERR) associated with the PE performance are effectively promoted by this precipitation hardening effect. Under the applied force of 20 mN (equals to the average contact pressure of 4.6 GPa) the DRR and ERR are 86.0% and 85.7%, respectively, which are higher than those of Ti50Ni25Cu25 ribbons crystallized and aged at 500 °C. Experimental results indicate that aging at a temperature lower than the crystallization temperature can effectively improve the mechanical and functional properties of amorphous Ti50Ni25Cu25 shape memory ribbon.