Compared with traditional gas compression refrigeration, solid-state refrigeration has become a research hotspot in the past decade for its unique advantages in energy conservation and environmental protection. Cooling based on the elastic heat effect of reversible martensitic phase change materials under the excitation of external force has great application potential. Key performance indicators such as the magnitude of temperature change, critical stress, phase transition hysteresis, and fatigue characteristics of the elastic heat effect depend not only on the intrinsic properties of the material such as phase transition entropy and chemical bond strength, but also are closely related to the material's micro-defects and microstructure. Therefore, effective control of the microstructure is the key to the material's elastic and thermal properties. Non-equilibrium solidification phase selection and crystallographic orientation control of metallic functional materials is a unique material preparation and processing method, which is expected to improve the elastic and thermal properties obtained by conventional methods.
In recent years, the New Magnetic Phase Change Materials team at the Ningbo Institute of Materials Technology and Engineering of the Chinese Academy of Sciences has reported the elastic heat effects of dozens of materials and systematically studied the effect of controlled solidification on the properties of elastic heat refrigeration materials. Recently, Pd-In-Fe single crystal, which is a new type of variable magnetic shape memory alloy, can theoretically obtain 15% tensile martensitic transformation strain and has huge elastic heat potential. The team prepared the Pd-In-Fe polycrystalline alloy by direct smelting and annealing. For the first time, the elastic and thermal effects of the Pd-In-Fe alloy were measured. It was found that Pd59.3In23.2Fe17.5 obtained 5.4 under the trigger of a critical stress of 80 MPa. The adiabatic temperature change of K. The results were published on Intermetallics (2018, v100, p27). Next, the team prepared the Pd-In-Fe alloy using the deep super-condensation technology of cyclic superheat and molten glass composites, and studied the superelastic and elastic heat effects. This solidification technology eliminates impurities in the melt by melting the glass, making the alloy nucleate and solidify at a temperature far below the liquidus temperature, avoiding the segregation and solidification process of the as-cast alloy, and directly obtaining a martensite phase with uniform composition At the same time, due to the large amount of internal gravity introduced by the deep undercooling process, a unique linear superelasticity was obtained at 361K. The hysteresis loss of linear superelasticity is reduced by 75% compared with the non-linear superelasticity of Pd-In-Fe annealed samples with equivalent strain. The deep undercooled alloy achieved an adiabatic temperature change of 3K under a uniaxial stress of 154 MPa. This unique linear hyperelasticity with small lag loss is conducive to the compactness and miniaturization of the system design. Related work was published in Scripta Materialia (2019, v160, p58) and applied for a patent (201811164007.1).
In addition, the team prepared a sample of large NiMnSn grains with orientation and deviation from this crystal orientation by liquid metal cooling with high temperature gradient directional solidification, and constructed grain orientation dependence to study elastic temperature and local strain under the same loading conditions. Sexual experimental conditions. Introduced a combination of infrared thermal imaging and digital image correlation technology to achieve real-time monitoring of the surface distribution of temperature and strain during the elastic thermal test. It was found that the strain distribution and temperature change distribution had obvious crystal orientation dependence, and localized areas were observed. Temperature change lags behind the unsynchronized phenomenon of strain. This work has important guiding significance for in-depth understanding of the stress-induced phase transition mechanism and the optimal elastic and thermal properties of mining materials.