Listen! It's a phase transition. The sound of a shape-memory alloy

TL;DR

This paper demonstrates that the phase transition in a shape-memory alloy can be detected through sound analysis, providing an accessible educational tool for understanding solid-to-solid phase changes.

Contribution

It introduces a simple, sound-based experimental method to qualitatively and quantitatively analyze phase transitions in shape-memory alloys for educational purposes.

Findings

Phase transition emits detectable sound signals.

Sound analysis correlates with temperature-induced phase change.

Method suitable for undergraduate teaching environments.

Abstract

Shape-memory alloys exhibit a solid-to-solid phase transition that involves a temperature-driven rearrangement of their crystal structure and is responsible for their remarkable properties and numerous technological applications. Here, we propose a simple experiment that analyzes the sound emitted by a Ni$_{40}$Ti$_{50}$Cu$_{10}$ bar at different temperatures as it undergoes a transition between its austenite and martensite phases. We show that the phase transition, which occurs slightly above room temperature, can be qualitatively detected by the ear and quantitatively described using a very simple experimental setup and sound analysis tools. Such a sound-based investigation provides an unusual and engaging way to experimentally introduce solid-to-solid phase transitions, that is suitable for undergraduate courses.