Nanoindentation studies on precipitation hardening of Ti-rich Ti50.4Ni49.5Si0.1 shape memory ribbons

Precipitation hardening effect in Ti-rich Ti50.4Ni49.5Si0.1 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 Ti2Ni precipitates and the ribbon aged at 773 K for 1 h is hardened by the coexistence of dense nanoscale Ti2Ni and Ti3Ni4 precipitates. The Ti3Ni4 formation is closely related to the Si content in the ribbons, which enhances the Ti2Ni 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 Ti2Ni and Ti3Ni4 precipitates in aged Ti50.4Ni49.5Si0.1 ribbons show not only significant precipitation hardening but also a substantial improvement in the functionality of the TiNi ribbons.