Abstract
In this study, the combined effects of strengthening, precipitates, and textures on the shape recovery ability and superelasticity of thermomechanically treated Ti49.3Ni50.7 shape memory alloy (SMA) in both the rolling and transverse directions were studied by experimental measurements and theoretical calculations. Experimental results and theoretical calculations showed that the 300 °C × 100 h aged specimen exhibited the best shape memory effect because it possessed the most favorable textures, highest matrix strength, and most beneficially coherent stress induced by Ti3Ni4 precipitates. The 30% cold-rolled and then 300 °C × 100 h aged specimen exhibited the highest strength and superelasticity; however, its shape recovery ability was not as good as expected because the less favorable textures and the high strength inhibited the movements of dislocations and martensite boundaries. Therefore, to achieve the most optimal shape memory characteristics of Ni-rich TiNi SMAs, the effects of textures, matrix strength, and internal defects, such as Ti3Ni4 precipitates and dislocations, should all be carefully considered and controlled during thermomechanical treatments.
Highlights
Near-equiatomic TiNi shape memory alloys (SMAs) are widely used in a variety of applications because of their excellent shape memory effect, superelasticity, high strength and ductility, and good damping capacity [1,2]
For polycrystal Ti49.3 Ni50.7 SMA with various thermomechanical treatments, the transformation temperatures, microhardness, shape memory effect, superelasticity, and orientation distribution functions (ODF) of specimens were measured and their theoretical recoverable strains were calculated by the lattice deformation theory
Experimental results and theoretical calculations demonstrated that thermomechanically treated specimens had varied superelasticity and recoverable strains corresponding to the alloys’ different microstructures, textures, and strengths
Summary
Near-equiatomic TiNi shape memory alloys (SMAs) are widely used in a variety of applications because of their excellent shape memory effect, superelasticity, high strength and ductility, and good damping capacity [1,2]. It has been reported that thermomechanical treatments, including work hardening, solid-solution strengthening, precipitation hardening, and grain refinement, normally strengthen TiNi SMAs by increasing the critical shear stress for slip [3,4,5]. The shape memory effect and superelasticity of thermomechanically treated TiNi SMAs can be improved by suppressing the irreversible slip deformation during the martensite reorientation and stress-induced martensitic transformation. Thermomechanical treatments may simultaneously change the textures and microstructures of TiNi SMAs, thereby influencing their mechanical properties. Numerous studies have reported the relationship between shape memory behaviors and the crystallographic properties of TiNi SMAs [6,7,8,9,10,11]. Shu et al [7] and Inoue et al [8]
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