The Roles of Stress and Pressure in Multicaloric Effects of Shape Memory Alloys: Mechanisms and Recent Advances

Abstract

Abstract

Shape memory alloys (SMAs) undergo reversible martensitic transformations that generate caloric responses and offer potential for solid-state cooling. This review critically examines how uniaxial stress and hydrostatic pressure regulate the caloric and multicaloric behavior of SMAs, with particular emphasis on their coupling with magnetic fields. Uniaxial stress acts directionally through transformation strain and variant selection, whereas hydrostatic pressure modifies phase stability through the transformation volume change between austenite and martensite. Their combined or sequential application with magnetic fields is analyzed in terms of phase fraction, transformation path, hysteresis, reversibility, and operating-temperature range. To clarify the available evidence, direct field-driven caloric responses are distinguished from processing-induced changes in microstructure and internal stress that indirectly affect subsequent caloric behavior. Recent experimental and theoretical advances are compared using caloric amplitude, loading and unloading responses, energy dissipation, cyclic stability, and applied-field requirements. The results show that appropriately designed coupled-field protocols may enhance caloric responses and reduce hysteresis in selected systems; however, these effects depend on alloy composition, microstructure, field magnitude, temperature, and loading sequence. Standardized measurements and coupled thermodynamic-kinetic models are therefore needed to support the development of reversible and durable multicaloric cooling systems under device-relevant fields.