Recently, Qian Suxin, associate professor of Xi'an Jiaotong University School of Energy, and collaborators have prepared additive-made fatigue-resistant high-performance elastic thermal refrigeration materials. On November 29, the relevant results were published online in Science.
Elastic thermal refrigeration is a new type of solid-state refrigeration technology. Compared with traditional vapor compression refrigeration working fluids, elastic thermal refrigeration working fluids such as nickel-titanium shape memory alloy do not have any greenhouse gas effect, and the energy density of the elastic thermal effect is significant. At present, the fatigue life of elastothermal working fluid is the primary factor restricting its engineering application, and the efficiency of elastothermal working fluid and elastothermal refrigerator also needs to be improved.
Focusing on the two key issues of improving efficiency and fatigue life, the team of Qian Suxin and researchers from the University of Maryland, Arms Laboratory, Colorado Mining University, Iowa State University and other institutions used powder laser directed energy deposition technology To prepare a nickel-titanium alloy material with a nano-composite structure, which can be directly shaped into columnar, tubular, honeycomb, etc. structures that can be applied to elastic heat refrigeration regenerators.
Unlike traditional melt-casting shape memory alloys, additive-made nickel-titanium alloys have a quasi-linear stress-strain response, hysteresis characteristics independent of loading rate, and significantly reduced phase transition hysteresis. The researchers found that the interface dislocation generated at the nano-scale Ni3Ti and NiTi grain boundaries can become the nucleation point of the phase transition process, effectively reducing the potential barriers to be overcome and reducing the friction loss at the phase interface. The above characteristics can improve the fatigue life, so that the elasto-thermal effect remains unchanged after millions of loading and unloading cycles.
In the case that the unloading work can be fully recovered, taking the standard working condition of GB / T7725 air conditioner as an example, the thermal perfection of the nickel-titanium alloy sample manufactured by additive manufacturing reaches 60%, which is nearly the thermal perfection of the traditional molten-cast nickel-titanium alloy. Times. (Reporter Zhang Xingyong)
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