Effects of cooling rate on martensitic transformation behavior and shape memory property for Ni-rich NiTiHf-Nb high-temperature shape memory alloy

Abstract

The NiTiHf-Nb alloy exhibits good workability as well as high-temperature shape memory property. In this work, effects of cooling rate on martensitic transformation behavior and shape memory property for Ni-rich (Ni 50.1 Ti 34.9 Hf 15 ) 85 Nb 15 alloy were investigated. For comparison, the martensitic transformation behavior and shape memory property of Ni 50.1 Ti 34.9 Hf 15 alloy were also investigated. As the cooling rate decreased from water cooling to furnace cooling after solution treatment, the martensitic transformation temperatures (TTs) of (Ni 50.1 Ti 34.9 Hf 15 ) 85 Nb 15 alloy decreased gradually, whereas the decrease was not obvious for Ni 50.1 Ti 34.9 Hf 15 alloy. The increased valence electron concentration (c v ) should account for the decrease in TTs of (Ni 50.1 Ti 34.9 Hf 15 ) 85 Nb 15 alloy. The shape memory effect strain increased with the decrease in the cooling rate for both two alloys, and the largest shape memory effect strain of 2.6% can be obtained in furnace-cooled (Ni 50.1 Ti 34.9 Hf 15 ) 85 Nb 15 alloy. This enhancement in the shape memory property should be ascribed to the precipitation of H-phase in furnace-cooled (Ni 50.1 Ti 34.9 Hf 15 ) 85 Nb 15 alloy. • Higher shape memory effect strain could be obtained by slow cooling after solution treatment. • Higher martensitic transformation temperatures could be obtained by fast cooling after solution treatment. • The martensitic start transformation temperatures were c v dependent. • Precipitation of H-phase could be improved by addition of Nb.