Design And Study Of High-working Temperature Ni-Mn-Sn Magnetic Memory Alloys

Due to the magnetic field-induced reverse martensitic transformation,the Ni-Mn-Sn magnetic shape memory alloys has large magnetic induced strain,giant magnetocaloric effect and magnetoresistance effect,which make Ni-Mn-Sn widely used in magnetic drive sensing,energy environment and data storage and other fields.However,it impossible to apply in high-temperature environment with the low operating temperature of the alloy,in addition to which the alloy will change the operating temperature according to diverse working environments.Thus,the development of a magnetic shape memory alloy with a high and tunable working temperature range is an urgent problem to be solved.The phase stability and magnetic properties of Ni-Mn-Sn alloy can be significantly improved by element doping and stress,which is expected to be an effective way to regulate its working temperature and operatin g temperature range.Hence,this thesis adopts three methods of element co-doping(Pt and Co),hydrostatic pressure and strain to increase the working temperature and extend the operating temperature range of the alloy,and reveals the influence of these factors on the martensite transformation behavior,magnetic properties,phase stability and phase transformation temperature of the alloy by the first-principles calculation method.The study found that the Curie temperature(T_C)and magnetization difference(?M)between the austensite and martensite phases are directly proportional to Co concentration in the alloy,while the martensitic the martensitic phase transition temperature(TM)is the opposite.Both the TM and TC of the alloy are positively correlated with the concentration of Pt.The high-temperature magnetic driven martensitic transformation of Ni-Mn-Sn alloy is realized by adjusting the co-doping ratio of Pt and Co elements.The prediction results show that the operating temperature of Ni₁₁Pt₃Co₂Mn₁₃Sn₃ alloy is 412 K,which can be used in high temperature environments.The calculations result is displayed that the T_M of the alloy is very sensitive to hydrostatic pressure.As the hydrostatic pressure increases,the energy difference between austenite and martensite increases,and the TM of the alloy increases;Besides,the doping of co elements can not only increase the T_C of the alloy but also increase the?M.Therefore,hydrostatic pressure can dynamically control the working temperature of the Ni-Co-Mn-Sn alloy.Under 0-3 GPa hydrostatic pressure,the operating temperature range of Ni₁₄Co₂Mn₁₃Sn₃ alloy is 256-338 K,which realizes wide operating temperature range(80 K)of alloys.Compared to hydrostatic pressure,strain has a larger control range.The calculation results show that the TM of Ni-Mn-Sn alloy significantly increases with the increase of biaxial strain.Conversely,the change of?M value of the alloy is negatively correlated with the biaxial strain.The biaxial strain is combined with the doped Co elements can ensure that the Ni-Mn-Sn alloy has a large?M,and widen the working temperature range.Under the action of biaxial strain of-1.0%to 1.5%,the working temperature range of Ni₁₄Co₂Mn₁₃Sn₃ alloy is 181-384 K,which meets the application requirements of high temperature environment.