Study On Mechanical And Magnetic Properties Of Ni-Mn-Sn-Fe Magnetic Shape Memory Alloy

Ni-Mn-Sn alloys can be subjected to a metamagnetic transition from the weak magnetic martensite to strong ferromagnetic austenite under an external magnetic field.This type of alloys have a high response frequency and a large output stress.Meanwhile,these alloys exhibit multifunctional properties and the richness and diversity of the physical phenomena due to the magnetic-field-induced phase transformation.However,the problem of brittleness and high magnetic drive threshold is a serious limitation of its application and development.In this paper,we achieve simultaneous enhancement of magnetic and mechanical properties in Ni-Mn-Sn alloy by adding Fe element.Ni50-xFexMn38Sn12(x=0,3 at.%)and Ni50-xFexMn39Sn11(x=0,3,4,6 at.%)magnetic shape memory alloy were prepared by vacuum arc melting method.The microstructures,martensitic transformations,mechanical,magnetic properties,and their influences on Ni-Mn-Sn magnetic shape memory alloys have been investigated by means of SEM,XRD,compressive tests.Clarified the Fe elements on the structure of the organization and the influence of phase transformation rule;By fracture analysis reveals that the Fe element of Ni-Mn-Sn alloys toughening mechanism;And through the primary principle reveals the Fe doping of Ni-Mn-Sn magnetic qualitative influence mechanism.Experimental results indicate that by substitution of Fe for Ni,the microstructure and crystal structure of the alloys change at room temperature.The second phase was induced and its content increases with Fe addition.Ni50-xFexMn38Sn12(x=0,3 at.%)and Ni50-xFexMn39Sn11(x=0,3,4,6 at.%)alloys undergo one-step thermoelastic martensitic transformation during the process of cooling and heating.Martensitic transformation temperatures of Ni-Mn-Sn alloys decrease with the increase of Fe content.Compression tests show that an appropriate amount of Fe addition has significantly improved the mechanical properties of Ni-Mn-Sn alloy.Both the compressive strength and strain have a strong dependence upon the Fe content.When there is 4 at.%Fe added,the compressive and maximum strain reach the maximum value(approximately 725.4 MPa and 9.3%),which were significantly improved than that of the alloy without Fe addition.with the further increase in Fe content,the compressive strain is decreased largely.It should be noted that,according to the DSC results,Fe6 alloy is austenite while others are martensite initially.Although the second phase formation increased the strength slightly.It also made the alloy more brittle.The fracture type changes from intergranular fracture to transgranular fracture with increasing Fe content.We found that enhancement of MFIRMT by Fe doping is originated from tuning antiferromagnetic austenite to ferromagnetic state by substitution of Fe for Ni.The martensitic transformation temperature can be quantified using the energy difference between the austenite and martensite phases.The Fe doping decreases the total energy difference between austenite and martensite of Ni-Mn-Sn,resulting in the decrease of its martensitic transformation temperature.