The Martensitic Transformation And Elastocaloric Effect Of Ni-Mn-Sn-Ti Magnetic Memory Alloys

The wide application of traditional vapor compression refrigeration technology has caused enormous pressure on the environment,so clean,environmentally friendly,green and energy-saving solid-state refrigeration has become a current research hotspot.Ni-Mn-Sn magnetic shape memory alloy has both magnetocaloric effect and elastocaloric effect,and can also realize coupling effect under magnetic field and stress field.It is a kind of high-efficiency refrigeration material with great potential.However,the intrinsic brittleness of Ni-Mn-Sn alloy limits its application in elastothermic refrigeration.For this reason,this paper proposes the idea of doping Ti element in Ni-Mn-Sn alloy to improve its mechanical properties on the basis of ensuring its elastocaloric properties.The microstructure,phase transition behavior and mechanical properties of Ni-Mn-Sn-Ti alloy were systematically studied by X-ray diffraction,differential scanning calorimetry,first-principle calculation,room temperature compression experiment,scanning electron microscope observation and thermocouple measurement and elastocaloric properties and microscopic mechanism.The study found that with the increase of Ti content,the martensite phase in the alloy structure at room temperature gradually disappeared.The results of differential scanning calorimetry show that the doping of Ti element significantly reduces the martensitic transformation temperature of Ni-Mn-Sn alloy,and when the Ti doping content increases by 1 at.%,the phase transformation temperature of Ni-Mn-Sn alloy decreases about 35K.The first-principle calculations show that the substitution of Ti for Ni reduces the total energy difference between Ni-Mn-Sn austenite and martensite phase,which is the internal reason for the decrease of martensite transformation temperature.Compression experiments at room temperature show that Ti doping can significantly improve the mechanical properties of Ni-Mn-Sn alloys.Proper amount of Ti element doping can enhance the compressive fracture strength and toughness of the alloy.When the Ti doping content is 1at.%,the Ni₄₃Mn₄₆Sn₁₀Ti₁ alloy has a compressive strength of 538 MPa and a fracture strain of～10%.Combined with the microstructure and fracture morphology,it was found that the fracture mode changed from intergranular fracture to transgranular cleavage fracture.The elastocaloric test results show that the elastocaloric properties and cycle stability of the alloy can be guaranteed after doping with an appropriate amount of Ti.At room temperature,the maximum adiabatic temperature of the Ni₄₄Mn₄₅Sn₁₀Ti₁alloy is 4.4 K after unloading 400 MPa stress,and the elastocaloric properties of the alloy remain basically unchanged after 15 cycles of loading and unloading.The above results show that Ti doping can provide a reference for the development of Ni-Mn-Sn magnetic shape memory alloys with excellent mechanical properties and obvious elastocaloric effect.