Experimental Study On Magneto-mechanical Coupling Behavior Of Ferromagnetic Shape Memory Alloys Ni₂MnGa

Ferromagnetic shape memory alloys(FSMAs)are a new type of functional material,which exhibit many outstanding advantages such as high ferromagnetism, large magnetostrain,thermoelastic and magnetic shape memory effect.Ferromagnetic shape memory alloys are potential in actuators application because its response frequency is as high as piezoelectric materials,strain-stress output can be compared with thermal shape memory alloys.In this paper,experiment on magneto-mechanical coupling behavior of Ni₂MnGa under magnetic field and stress are systemically studied.Firstly,the micro-mechanism and behavior of magnetostrain of single crystal Ni₂MnGa ferromagnetic shape memory alloys has been expatiated based on references.Ni₂MnGa exhibits pseudoelastic behavior,when the material is applied at low magnetic field(1＜H＜3 kOe),the pseudoelastic behavior is partial.Ni₂MnGa single crystal,because of highly-preferred twin variants,can produce huge magnetostrain under magnetic field,magneto-mechanical coupling is strong.Secondly,the effects of applied axial pre-compressive stresses and magnetic fields on the magneto-mechanical characteristics of ferromagnetic shape memory alloys Ni₅₂Mn₂₇Ga₂₁and Ni₅₄Mn₂₅Ga₂₁polycrystalline samples have been studied experimentally with self-designed equipment.The magnetization curves and magnetization hysteresis loops measured along axial direction of the two kinds of samples with different inclination angles of applied magnetic fields and axial pre-compressive stresses were obtained,as well as stress-strain loops and magnetostrain curves.The experimental results showed that the saturation magnetization values measured along axial direction of the samples decrease with the inclination angle of applied magnetic fields increases.The pre-compressive stresses have no obvious effect on the magnetization curve and magnetization hysteresis loop. The applied magnetic fields with different inclination angles show little effect on the stress-strain loop.Magneto-mechanical coupling of Ni₂MnGa Polycrystals is weak.