THERMOELASTIC MARTENSITIC TRANSFORMATION AND SHAPE MEMORY EFFECT IN NANOPLATES BASED ON TI–NI ALLOYS: EXPERIMENT, MODELING BY DENSITY FUNCTIONAL THEORY AND MOLECULAR DYNAMICS

Abstract

Nanoplates based on Ti–Ni alloys, exhibiting a thermoelastic martensitic transition at the critical temperature Tc, are investigated experimentally by transmission electron microscopy. It is shown that the Tc(h) dependence strongly decreases. There is a critical thickness hc at which the transition is completely suppressed. As a result of the combined ab initio simulation by the methods of density functional theory and molecular dynamics, it is demonstrated that austenite is more stable than martensite in nanoscale plates. The phase transition is completely suppressed in a 10-nm-thick plate, which is in good agreement with the experimental value of hc. In a transmission electron microscope during heating and cooling, the reversible shape memory effect in composite amorphous-crystalline Ti2NiCu samples is for the first time demonstrated while simultaneously observing the evolution of the structure of martensitic twins and the shape. The studies are carried out on ultrathin wedge-shaped samples with a thickness of 200 to 30 nm, made in the form of a composite bimetallic nanoactuator.