Mechanism of the influence of poly- and nanocrystallinity on the parameters of pseudoelastic deformation curves of alloys with the shape memory effect

The influence of poly- and nanocrystallinity on the parameters of pseudoelastic deformation curves of alloys with the shape memory effect (SME) has been analyzed within the theory of diffuse martensitic transformations. The functional and quantitative dependence of the coefficient of deformation (martensitic) hardening of an alloy with the SME on the grain size d and orientational factor $M$, $d\sigma/d\varepsilon\sim1/Md^{2}$, has been obtained for the first time, taking into account the normal distribution density of grains over their orientations and the log-normal distribution density over grain sizes $d$. A comparison of the found dependence with the data in the literature for a nanocrystalline TiNi alloy with nanograin sizes in the range of 8–90 nm shows good consistency between the theory and experiments.