Study On Mechanical Constitutive Model Of Polycrystalline Ferromagnetic Shape Memory Alloy Ni-Mn-Ga In Directional Solidification Under Coupling Multiple Fields

Ferromagnetic shape memory alloys possess some characteristics,such as strong ferromagnetic,large magnetostriction and so on,which make them as a new generation of materials as actuators and sensors,and it is expected to be applied to aviation,aerospace,engineering,medicine and other fields.There is initial texture in the unidirectionally solidified ferromagnetic shape memory alloys,the grain orientation preferred direction of solidified direction,which improved the mechanical properties of materials.The preparation method simple and low-cost,and the alloy have a high compressive strength,so it has been widely used.Polycrystalline ferromagnetic shape memory alloys Ni-Mn-Ga samples prepared by unidirectional solidification are studied in this paper,the main research content is as follows:In order to improve the macroscopic strain of the material under external fields,mechanical training at first,namely alternately application of compressive stress in two mutually perpendicular directions of the specimens.After the mechanical training,the grain size can be increased,the number of martensite variant can be reduced,and the interference of twin boundaries moving with each other can be weaken.For analysis the impact of mechanical training to material initial texture and other microscopic structure,this paper selects two groups of polycrystalline Ni-Mn-Ga samples,which have same size.We measure the initial texture change before and after mechanical training,analysis the form of initial texture,then we got the three dimensional orientation distribution,through it,we quantitative analysis the volume fraction of texture.Next,under coupling multiple fields,thinking the impact of texture to materials anisotropic mechanical properties,we established constitutive model,with micromechanics method and thermodynamic principle.At last,application of the established model,we analysts forecasts the different process orientation materials' macroscopic mechanical behavior under mechanical-magnetic and magnetic-temperature field.Then,the theoretic result proved well by comparison with experimental data.Some useful conclusions are obtained,which may provide guidance for the materials used in engineering.