Effect Of Element Substitution On The Structure And Properties Of Ni-Co-Mn-Sn Magnetic Shape Memory Alloys

Ferromagnetic shape memory alloys (FSMAs) showing shape memory effect and magnetic property, have attracted extensive attention wildly due to their multi-functional properties that include significant magnetically controlled shape memory effect, magnetoresistance effect, and magnetocaloric effect.The shape memory mechanism of Ni-Mn-Sn magnetic shape memory alloy is magnetic-field-induced phase transition. When the parent phase is near the martensitic transition temperature, imposing a magnetic field to induce a martensitic transition will cause initiate macroscopic deformation. The driving force of magnetic-field-induced phase transition is Zeeman energy between austenite and martensite, its output stress could reach up to 100 MPa, much higher than that by traditional Ni-Mn-Ga magnetic-field-induced martensite variants rearrangement, whose stress is only 2-5 MPa. The saturated magnetization difference △M increases with different ferromagnetic exchanges between austenite and martensite in Ni-Mn-Sn alloy, so Zeeman energy rises.The martensitic transition temperature in Ni-Mn-Sn alloys was related to the valence electron concentration e/a, and could be changed by two main methods, one is altering the components of the alloys, and the other one is elements substitution. Addition fourth component elements such as Co, Cu, and Fe in this kind of alloy could improve martensitic transition temperature and reduce the magnetic field requried to induce martensitic transition.In this research, by the method of changing compositions, I studied the influence of different components and elements substitution of Ni-Co-Mn-Sn alloys on their structure and properties, analyzed the effects of elements substitution on structure, phase transition temperature, hysteresis, phase transition temperature range and magnetic properties. The final purpose is to obtain alloys with lower hysteresis, smaller phase transition temperature range, and larger △M.Experiments shows, the martensitic transition temperatures of Ni50-xCoxMn41Sn9 (x=6,8,9,10,11), Ni50-xCoxMn43Sn7 (x=8,11,12), Ni41-xCuxCo9Mn4oSn10 (x=0,0.5,1,2), andNi40.5Co9.5Mn40Sn10-xAlx (x=0,0.5,1,2,3) were all above room temperature, there were a variety of mixed state martensites when under room temperature, and the main structure was tetragonal. The lattice parameters changed by elements substitution, Co substitution induces a increased, c decreased and cell volume increased; the substitution of Cu and Al reduced a and cell volume. The martensitic transition temperature of Ni37Cu4Co9Mn40Sn10 was below room temperature, the structure was L21 of austenite.The phase transition temperature changed obviously with different compositions, it decreased with Co, Cu, and Sn substitution, and rised with the increase of Al. The influence of valence electron concentration and cell volume on Ni40.5Co9.5Mn40Sn10-xAlx, the latter accounted for the primary role. The transformation hysteresis As-Mf increased with Co content increasing in Ni50-xCoxMn41Sn9 alloy system. I got 3.44℃ martensitic transition range in Ni37Cu4Co9Mn40Sn10, which is helpful for getting larger magnetic entropy change.The magnetic susptibility increased with Co, Cu, and Sn increasing, decreased with Al increasing.