Influence of crystallographic compatibility on residual strain of TiNi based shape memory alloys during thermo-mechanical cycling

Instability of cyclic superelastic deformation of NiTi investigated by synchrotron X-ray diffraction

“…This all suggests that the activity of the hybrid slip/transformation process depends on the starting microstructure (grain size, internal stress, precipitates). Furthermore, it is also possible that the amount of dislocations generated by the moving austenite/martensite interfaces is linked to the accommodation of transformation shear and volume mismatch at the austenite/martensite interface [34] -i.e. to the crystallographic incompatibility between the transforming phases (the higher the incompatibility, the more dislocation slip occurs).…”

Twinning-Induced Elasticity in NiTi Shape Memory Alloys

“…These effects are documented for PE NiTi in the literature and they are often referred to as functional fatigue (e.g., [9,73,75]). In the case of SMAs showing PE or the 1WE, functional fatigue is related to the generation of microstructural defects, such as dislocations and stabilized martensite during repeated phase transformations [21,30,73,[75][76][77]. This is not the case for TIE SMAs, where phase transformations are not involved.…”

Structure–property relationships in a precipitation strengthened Ni–29.7Ti–20Hf (at%) shape memory alloy

“…Tang [2] has summarized the work of many groups concluding that small increases in Ni content for compositions above 50 at.% resulted in a precipitous drop in the transformation temperatures to well below room temperature. However, unlike the equiatomic and Ti-rich compositions, which generate significant residual strains during thermomechanical cycling through the transformation regime [1,3,4], the Ni-rich compositions exhibit excellent dimensional stability during pseudoelastic stress cycling and load-biased thermal cycling because of precipitation strengthening effects [5][6][7]. Dimensional stability refers to the material maintaining a fixed dimensional tolerance during multiple transformation cycles, an attribute critical in actuator based applications.…”