Pseudoelastic behavior of nickel–titanium melt-spun ribbon

The pseudoelastic behavior of NiTi shape memory alloys (SMAs) is known to be sensitive to alloying and prior thermal history, but relatively little has been established concerning the influence of grain size, especially in the nanoscale regime. The research reported, employs the technique of melt spinning to create continuous ribbons of equiatomic NiTi alloys. This technique yields fine ribbons, approximately 30 μm thick, and ranging in length from a few millimeters to several centimeters. Tensile testing was conducted on the ribbon material in the as-spun condition at temperatures from 40 to 85 °C. Little appreciable pseudoelastic behavior was observed in this temperature range, even after aging for 1 h at temperatures ranging from 300 to 600 °C. However, the mechanical properties were dramatically improved and the grain size in the melt-spun ribbon was further refined by repeated cold rolling. The resulting material displayed reduced grain size at the nanometer scale with the primary phase remaining B2 NiTi. This cold-worked material exhibited strong pseudoelastic behavior not observed in the as-spun ribbon, and did so without the use of a heat treatment step. The cold-rolled melt-spun ribbon also exhibited a significantly diminished mechanical hysteresis stress.