Authors: Yang Hu, Guodong Cui, Wuqian Chai, Jinbao Zhang, Junying Chen and Chuan Yang
Abstract: The effect of annealing temperature on the microstructure and magnetic properties of Fe-N-Ni-P powders was described. The mixed powders of Fe0.64Ni0.36 and Ni3P were prepared by electroless nickel-phosphorus plating on Fe-N powder and annealing at range from 600 ℃ to 750 ℃ for 1hr in vacuum. The phase composition and microstructure of synthesized powders were investigated by optical microscope (OM), X-Ray Diffraction (XRD), scanning electron microscope (SEM) and vibrating sample magnetometer (VSM). Microstructure of sections of metallographic specimen and XRD analysis revealed that the Fe-N-Ni-P powder from γ’-Fe4N, ε- Fe3N, and amorphous Ni-P coating change to FeN0.0499, γ’-Fe4N, Fe-Ni solid solution, and Ni3P at annealing temperature of 600 ℃. When the annealing temperature more than 650 ℃, all Fe-N phase was transformed to Fe0.64Ni0.36 phase. Size of the calcined powders formed big agglomeration (cohesive body), determined by SEM, was in the range from 2 to 7 μm and decreased with annealing temperature growth due to the grain growth, and average thickness of Ni-P coating was about 0.5 μm, which has effect on magnetic properties. The prepared powder at 600 ℃ showed saturation magnetization (Ms) of 94.1 emu/g and coercivity (Hc) of 97 Oe, while the prepared powders at 750 ℃ presents the better saturation magnetization (120 emu/g) and the smaller coercivity (77 Oe). Such magnetic properties can be effected by alloy phase and impure phase, and the change of magnetic properties was discussed by the observed micro- structure features.
Keywords: composite powder; annealing temperature; magnetic properties; microstructure