Physical Properties Of Magnetic Shape Memory Alloy/Terfenol-D Composites

In the magnetic shape memory alloys,temperature,stress and magnetic field may induce martensitic transformation or martensitic variant rearrangement,resulting in drastic changes in physical properties such as strain effect,endothermic and exothermic effect,magnetic induced strain and transport properties.This kind of material has great application prospects in many fields such as magnet,magnetoelectrics,magnetic refrigeration and so on.The coupling stress,magnetic field,stress and temperature act together on magnetic shape memory alloy,which can effectively improve some application properties of materials,for example,the temperature range of martensitic transformation induced by magnetic field can be enlarged.Giant magnetostrictive materials can provide tremendous stress and strain under magnetic field.The composite of giant magnetostrictive material and magnetic shape memory alloy can exert stress on magnetic shape memory alloy and make the magnetic field and stress act together on magnetic shape memory alloy without the aid of external device.Firstly,this thesis focuses on Tb_0.27Dy_0.73Fe_1.9/Fe composites and Tb_1-xNd_xFe₃(x=0-1)series alloys.The effect of sintering process on magnetostrictive properties of giant magnetostrictive materials after forming composite materials was studied.Then the magnetic shape memory alloy and giant magnetostrictive material were compounded to study the effect of stress and magnetic field coupling on the physical properties of magnetic shape memory alloy under the stress of the giant magnetostrictive material.Some conclusions which have guiding significance for the practical application of materials have been obtained through the experiment.The main findings are as follows:The magnetostrictive properties of Tb_0.27Dy_0.73Fe_1.9/Fe composites were studied.It was found that the compressive stress affected the magnetostrictive properties of the composites during plasma sintering.The magnetostrictive properties perpendicular to the pressure direction are better than those parallel to the compressive stress direction.With the increase of Fe content,the saturation magnetostriction coefficient of Tb_0.27Dy_0.73Fe_1.9/Fe composite decreases.However,when the volume ratio of Tb_0.27Dy_0.73Fe_1.9 to Fe is 4:1,the magnetostriction of the composites does not decrease in the low field.It can be seen that the addition of Fe does play an auxiliary role in enhancing magnetization by external magnetic field.Tb_1-xNd_xFe₃(x=0-1)series alloys were composed by arc melting.It was found that when the Nd content was less than 0.6,the main phase of the alloys was PuNi₃ cubic structure.The magnetic measurements show that the saturation magnetization of the alloy decreases first and then increases with the increase of Nd content.The results of magnetostriction measurements show that the saturation magnetostriction of Nd-doped alloys is lower than that of TbFe₃ alloys.However,when the magnetic field is lower than2000 Oe,the magnetostrictive properties of Tb_0.6Nd_0.4Fe₃ alloy are better than that of TbFe₃ alloy,which is expected to be a candidate material for magnetostrictive applications in low field.The martensitic transformation characteristics of Ni₅₂Mn_24.5Ga_23.5/Tb Fe_1.9 and Ni₅₂Mn_24.5Ga_23.5/Tb_0.27Dy_0.73Fe_1.9 plasma sintered bodies were studied.It was found that the incorporation of Tb_0.27Dy_0.73Fe_1.9 and Tb Fe_1.9 enlarged the martensitic transformation temperature range and affected the structure of martensitic phase.However,the martensitic transformation of plasma sintered alloys is not affected by the external magnetic field.Compared with the Ni₅₂Mn_24.5Ga_23.5/Tb_0.27Dy_0.73Fe_1.9 binder of the same composition,it is found that the martensitic transformation behavior of plasma sintered alloys is affected by the spontaneous deformation at Curie temperature of Tb_0.27Dy_0.73Fe_1.9 alloy.