# Study on Nanoindentation Properties of FCC/B2 Nanostructured Films with Superelastic NiTi Interlayers

## TL;DR

This study uses simulations to explore how nanostructured films with superelastic NiTi layers behave under indentation, revealing how these layers reduce hardness and control deformation.

## Contribution

The study introduces a novel atomic-scale analysis of nanostructured films with superelastic NiTi interlayers and their mechanical behavior.

## Key findings

- NiTi interlayers reduce hardness by enabling large-scale phase transitions instead of dislocation propagation.
- Thicker surface films lead to more horizontal slip planes in the upper Ni layer.
- The B2-phase NiTi blocks dislocation and stacking fault propagation, reducing local deformation misalignment.

## Abstract

Dual-phase layered microstructures containing alternating regions of soft and hard phases can produce alloys with a unique combination of strength and ductility. In this study, the molecular dynamics (MD) method was utilized to simulate nanoindentation of a Ni/NiTi/Ni nanostructured film (NSF). This film features a unique alternating FCC/B2/FCC microstructure, in which the B2-phase NiTi acts as a superelastic shape memory alloy (SMA). The results indicate that Ni/NiTi/Ni NSF significantly reduces its hardness due to the superelasticity of the B2 phase. The presence of the NiTi interlayer effectively blocks the propagation path of dislocations and stacking faults by transforming the local dislocations transferred from the upper layer into a large-scale coordinated phase transition, significantly reducing local deformation misalignment. As the thickness of the surface film λ increases, the dislocation slip plane propagating horizontally appears in the upper pure Ni layer. The thicker the surface film, the more horizontal slip planes are formed. This study provides new insights into the contact mechanical behavior of nanostructured films based on NiTi shape memory alloys from the perspective of atomic scale.