Microstructure and mechanical properties of constrained shape-memory alloy nanograins and nanowires

TL;DR

This study uses phase-field modeling to explore how nanoscale constraints affect martensitic transformations and mechanical properties of shape-memory alloy nanostructures, revealing unique microstructures and size-dependent behaviors.

Contribution

It provides new insights into the microstructural evolution and mechanical response of constrained shape-memory alloy nanowires and nanograins at the nanoscale.

Findings

Microstructures such as dots on a square lattice can form under constraints.

Mechanical response varies with microstructure and size, showing non-monotonic yield stress.

Narrow wires exhibit pseudoelasticity, wider wires show shape memory behavior.

Abstract

We use the phase-field method to study the martensitic transformation at the nanoscale. For nanosystems such as nanowires and nanograins embedded in a stiff matrix, the geometric constraints and boundary conditions have an impact on martensite formation, leading to new microstructures --such as dots aligned on a square lattice with axes along <01>-- or preventing martensite formation altogether. We also perform tension tests on the nanowires. The stress-strain curves are very different from bulk results. Moreover, they are weakly affected by microstructures -- the mechanical response of nanowires with different microstructures may be similar, while nanowires with the same microstructure may have a different mechanical behavior. We also observe that at the transition temperature, or slightly below it, the narrowest wires behave pseudoelastically whereas wider wires are in the memory-shape regime. Moreover the yield stress does not change monotonically with width: it has a minimum value at intermediate width.