激光增材制造FeNi坡莫合金及其磁性能研究

Study on the laser additive manufacturing of FeNi permalloy and its magnetic properties

以Fe-50%Ni预合金粉末为原材料,并采用激光选区熔化(Selective laser melting,SLM)技术制备坡莫合金,通过光学显微镜、X射线衍射、扫描电子显微镜等对采用不同工艺参数制备的SLM Fe-50%Ni合金的微观组织进行观察表征,分别在直流及交流条件下采用磁性能测试仪对其稳态磁性能及动态磁性能进行测试分析,其中直流测试中最大外磁场强度为5000 A/m.同时,研究了在交流条件下外磁场强为10 mT时不同频率下的铁损变化.研究结果表明:随着扫描速度的降低,即激光体积能量密度的增加,合金样品的孔隙率降低,显微硬度升高,但是过高的能量密度也使得热应力增加而产生微裂纹,晶粒尺寸也较大;合金样品的主相均为γ-(Fe-Ni)相,微观组织主要为沿打印方向的柱状晶组织,但在其熔池边界附近也存在少量的等轴晶,晶粒大小呈现微观不均匀性;选择适合的能量密度对合金的内部质量及性能至关重要,在使用较适合的体积能量密度制备的SLM合金样品的相对孔隙率低于0.5%、矫顽力为270 A/m、饱和磁感应强度为1.2 T、剩余饱和磁感应强度为0.4 T;当磁场强度为10 mT时,随着频率从10 kHz增加至100 kHz,铁损随着频率的升高而升高.

This study focuses on the microstructure and magnetic properties of Fe-50 wt. % Ni permalloy be processed from the pre-alloyed powder by selective laser melting(SLM). SLM alloys were characterized by an optical microscope,scanning electron microscopy,X-ray diffraction,etc. The effects of the scanning speed on porosity, microstructure, and microhardness were evaluated and discussed. The magnetic properties were analyzed by magnetic property tester under DC and AC conditions, respectively. The evolution of iron losses at different frequencies with an external magnetic field of 10 mT under the AC condition was also studied. The results show that the relative porosity of SLM samples decreases with the decrease of scanning speed. And the microhardness of the SLM specimens increases with the decrease of scanning speed. However,very low scanning speed also leads to very high energy density,resulting in microcracks and large grain size due to the increase of thermal stress. Only the γ-(FeNi)phase was detected in the XRD patterns of the SLM permalloys manufactured from the different scanning speeds. The microstructure of the SLM parts is a typical columnar structure with an oriented growth of building direction. Also,there are a small number of equiaxed grains,especially near the boundary of the molten pool. In the SLM samples prepared with more suitable energy density,the relative porosity of the samples is less than 0. 5%,the coercivity is about 270 A/m,the saturated magnetic induction intensity is 1. 2 T,the residual saturated magnetic induction is 0. 4 T,and the iron loss increases with the increase of frequency when the magnetic field intensity is 10 mT.