Effects of processing parameters and heat treatment on the microstructure and magnetic properties of the in-situ synthesized Fe-Ni permalloy produced using direct energy deposition

The present work investigated the correlations between heat treatment and the microstructure and magnetic properties of the in situ alloyed Fe-50%Ni samples manufactured using laser-based direct energy deposition under different production conditions. The samples with high relative density were directly synthesized from the pure Fe and Ni elemental powders. In addition, a fine FCC microstructure with relatively elongated grains in the building direction was observed in the as-print samples. After applying short-time heat treatment, the grain morphology remained unchanged, while the grain size and microhardness were slightly increased and decreased, respectively. This also caused the reduction in internal residual stresses and, subsequently, partial stress relaxation in the microstructure. According to the electron probe microanalysis results, the simultaneous Fe and Ni depletion/enrichment formed during the in-situ alloying was practically decreased after applying short time heat-treatment, resulting in the significant improvement of magnetic properties, as compared to the as-built ones. The maximum magnetization, coercivity, and curie temperature of ~170 emg/g, 1.8 Oe, and 530 °C, respectively, were obtained in the optimum processed sample, which were significantly higher than those of other soft magnetic permalloys produced by additive manufacturing methods.