Effect of Rolling Temperature and Annealing on Grain Refinement in TiNiCu Shape Memory Alloys

Grain size refinement is a highly desirable characteristic in TiNi-based shape memory alloys (SMA) because they prevent the loss of recoverable strain. The current study elucidates the role of rolling temperature on grain refinement in TiNiCu shape memory alloy. The control of deformation temperature, ranging from room temperature to cryogenic temperatures, allowed for control over the stored energy in the rolled samples. Observations revealed that the as-rolled samples stabilized the deformation-induced austenite phase below the martensite finish temperatures, effectively inhibiting the phase transformation. Consequently, this resulted in constant electrical resistivity values. However, subjecting the samples to heat treatment under similar conditions led to varying grain sizes, ranging from a few hundred nm to tens of microns. This subsequently restored the B2 -> B19 ' transformation. These findings signify the importance of rolling temperature on grain refinement in TiNiCu SMAs. Lower rolling temperature correlated with coarser grain size due to higher stored energy driving the early recrystallization and grain growth.