Orientation Behavior Of Cr₇C₃Imposed By Magnetic Field

Material is the material basis for the survival of the society, the application anddevelopment of which plays an essential role for the process of the national economy andscientific technology. With the rapid development of the world technology, everyrequirement of the material properties in industrial production turns to be strict andaccurate. As the main approach to improve the material properties, the development andapplication of new technique in the process of material preparation has aroused universalattention by research scholars in the field of material science.The magnetic field not only can impact the macro process of physical or chemicalreaction, but also can produce high-intensity energy transmitted into material without anycontact. As a result, the thermodynamic state such as match and arrangement of atom ormolecule are changed, as well as material structure and phase change process. Thus, themicrostructure and properties of the material can be influenced dramatically. Therefore,the use of magnetic field has opened a new area in materials science in order to controlthe material preparation.This paper studies about the surfacing of Fe-based alloy, plasma arc surfacingequipment was applied to weld the powder on low carbon steel with introducedlongitudinal magnetic field. Analysis and detection of the surfacing layer were conductedwith ternary phase diagram and a large number of testing equipment. The distributionand morphology of carbide hard phase in the surfacing layer under different magneticparameter were studied. The growth mechanism of precipitated phase grain in magneticfield was given, along with the theory to explain the phenomena of its directionalalignment in regularity.The research result shows that a large number of M₇C₃carbide was formed in thesurfacing layer during plasma arc welding Fe5alloy. The hard phases are mainlyirregularly distributed in the form of block or strip shape without magnetic field, andshows no significant orientation. The distribution and morphology of the carbides begin to change with the application of longitudinal magnetic field. With the effect of DCmagnetic field, when the current is3A, M₇C₃was mostly showed in the shape of regularhexagon. The XRD analysis indicates that in this case, the main diffraction peakcorresponding to （060） plane of Cr₇C₃. The AC magnetic field shows little influence onorientation than DC magnetic field, meanwhile, the effect of the current on grain growthdirection is stronger than the frequency. Moreover, according to the theoretical, magneticmoment is the driving force for paramagnetic crystals with magnetic anisotropy to rotatein the magnetic field. As to Cr₇C₃crystal, the mechanism of its alignment fits to therotated orientation model, and after the form of rotation, it may turns into preferentialgrowth.