Nanoscopic size effects on martensitic transformations in shape memory alloys

The effect of the grain size and transverse film size in nano-and micrometer ranges on the parameters of martensitic transitions in shape memory alloys is theoretically considered in the framework of the theory of diffuse martensitic transitions. A quantitative analysis of the size effects is performed including not only the thermodynamic aspect of the martensitic transformation but also its kinetic aspect, which is particularly sensitive to structural and size factors. This complex approach makes it possible to explain the following three basic facts associated with the influence of a decreased grain size or transverse film size on the parameters of the martensitic transition in shape memory alloys: a decrease in the critical (characteristic) transition temperature, an increase in the transition temperature smearing, and the existence of a critical grain size or film thickness below which the martensitic transformation in alloys is blocked.