Effect mechanism of diamagnetism element Cu in-situ alloying on the microstructure and magnetic properties of SLM-formed NiFeMo alloy

NiFeMo alloy formed using additive manufacturing techniques with high saturation magnetic induction (BS) and low coercivity (HC) are crucial in aerospace applications. In this study, we successfully formed Cu-modified (NiFeMo)100-xCux alloys via in-situ alloying selective laser melting (SLM). The effect of in-situ alloying Cu content on the microstructure and magnetic properties of SLM-formed NiFeMo has been investigated, and efforts have been devoted to developing new technologies for modulating the properties of SLM-formed magnetic materials. The microstructure and magnetic properties of the alloy samples were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscattering diffraction (EBSD), DC B-H hysteresis loop tester (MATS-2010S), and transmission electron microscopy (Titan-G2). The results demonstrate that (NiFeMo)100-xCux alloys possess an FCC gamma-(Ni, Fe) solid solution structure within the range of added Cu content in this study. In the central region of the melt pool, columnar crystals grow in the direction of the temperature gradient, and the average grain size (D) decreases gradually with increasing Cu content from in-situ alloying. Cu atoms induced changes in the crystal structure by displacing atoms in the gamma-(Ni, Fe) solid solution, resulting in lattice distortion. The (NiFeMo)98Cu2 alloy exhibited an average crystal plane spacing d of about 0.2261 nm along the (111) gamma-(Ni, Fe) direction and a lattice distortion Delta epsilon of about 1.09 %. The saturation magnetic induction varied with increasing Cu additions, exceeding 0.7 T for NiFeMo alloy with Cu additions of 0.8 wt%, 1.1 wt%, and 1.4 wt%. The coercivity generally decreased with increasing Cu content, attaining values below 17 A/m when Cu (x = 0.5 wt%, 0.8 wt%) was added to the NiFeMo alloy. Therefore, controlling the in-situ alloying Cu content within the range of 0.8-1.4 wt% is beneficial for enhancing the soft magnetic performance of the SLMformed NiFeMo alloy.