Low driving-force stable bending cooling via fatigue-resistant hierarchical NiTi shape memory alloy

TL;DR

This paper introduces a bending-based elastocaloric cooling method using NiTi shape memory alloys that achieves low driving force, high fatigue resistance, and significant temperature drops, promising environmentally friendly refrigeration.

Contribution

It presents a novel bending approach for elastocaloric cooling with hierarchical microstructure and residual stress to enhance fatigue life and efficiency.

Findings

Achieved a 0.91 K temperature drop with low driving force.

Demonstrated over 5 million cycles with high fatigue resistance.

Developed a pre-strained laser shock peening method to improve microstructure.

Abstract

Elastocaloric cooling with shape memory alloys (SMAs) is emerging as a promising candidate for next-generation, environmentally friendly refrigeration. However, its development is hindered by the large driving force and low efficiency associated with uniaxial loading modes. In response, we present an innovative elastocaloric air cooling approach that utilizes the bending of NiTi beams, offering a low-force and energy-efficient solution. We achieve a continuous maximum temperature drop of 0.91 K and a dissipated energy of 15.1 N mm at a low specific driving force of 220 N. Notably, the specimen achieves over 5 million cycles under a maximum surface tensile strain of 1.94% for macroscopic cyclic bending, via a pre-strained, warm laser shock peening (pw-LSP) method. This unprecedented fatigue resistance originates from the formation of a hierarchical microstructure and a large compressive residual stress of over 1 GPa. This work demonstrates the great potential of bending induced elastocaloric cooling in the near future.