Nanoindentation studies on precipitation hardening of Ti-rich Ti_(5o.4)Ni_(49.5)Si_(0.1) shape memory ribbons

摘要

Precipitation hardening effect in Ti-rich Ti_(5o.4)Ni_(49.5)Si_(0.1) shape memory ribbons is investigated. The hardness of the ribbon aged at 773 K for 1 h reaches a maximum. TEM observations show the as-spun ribbon is strengthened by nanoscale Ti_)2Ni precipitates and the ribbon aged at 773 K for 1 h is hardened by the coexistence of dense nanoscale Ti_2Ni and Ti_3Ni_4 precipitates. The Ti_3Ni_4 formation is closely related to the Si content in the ribbons, which enhances the Ti_2Ni formation and thus makes the matrix Ni-rich. The ribbon aged for 1 h exhibits excellent reversible strain of shape memory effect and remnant depth ratio of pseudoelasticity. The nanoscale Ti_2Ni and Ti_3Ni_4 precipitates in aged Ti5o.4Ni49.5Sio.! ribbons show not only significant precipitation hardening but also a substantial improvement in the functionality of the TiNi ribbons.