Directional Solidification,Martensitic Transformation And Stress Analyze Of Ni-Mn-Ga Magnetic Shape Memory Alloys

The single crystal of Ni-Mn-Ga alloys have been prepared by the directional solidification; the characters of martensitic transformation have been investigated by means of electrical resistivity measurement, thermal expansion measurement, Differential Scanning Calorimeter (DSC) measurement, optical microstructure etc.; The stress distribution of martensitic transformation in single crystal Ni54.48Mn21.69Ga23.33 alloys has been investigated by means of ANSYS simulation.The shape of martensite is lens during cooling and martensites grow along crystal and more austensites transform into martensites during cooling; martensite variants of some diffrent orientation and inercross reform in equal axis zone and large parallel martensites reform in column zone.The rate of draw rod affected on the scale of single crystal obviously during the directional solidification:the fewer of the rate and the larger of single crystal;the thermal coefficient affected on the increment of crystal obviously; the volatile Mn leaded to the increace of transformation temperature Ms and affected on the scale of crystal.The surface flaws after increment indicated the existence of organization and thermal stress in the inter crystal.the node average stress-strain and the element average stress-strain is accordant in one martensite and two martensites; the shape and volume fraction affected on the stress and strain apparently; the larger of long axis/short axis is the larger of stress and strain; the more of martensites are the larger of stress and strain; the distribution of martensites affects on the stress and strain: the amount of stress and strain in two parallel linear and vertical distribution was increasing gradually ; the edge of model is sharp and it leaded to the concentration of stress . the comparison of literature and simulation results were the agreeable tendency qualitatively.