Finished surface morphology, microstructure and magnetic properties of selective laser melted Fe-50wt% Ni permalloy

Abstract

This work focuses on the structure and magnetic properties of Fe-50wt% Ni permalloy manufactured from the pre-alloyed powder by selective laser melting (SLM). The selective laser melted (SLMed) alloys were characterized by a 3D profilometer, optical microscope, scanning electron microscope, X-ray diffraction, etc. The effects of the volume energy density of laser (LVED) on structure, and magnetic properties with coercivity (Hc), remanence (Br), and power losses (P50-1), were evaluated and discussed systematically. The results show that the relative porosity rate and the surface roughness of the SLMed specimens decreased with the increase in LVED. Only the γ-(FeNi) phase was detected in the X-ray diffraction patterns of the SLMed permalloys fabricated from the different LVEDs. Statistical analysis of optical microscopy images indicated that the grain coarsened at higher LVED. Furthermore, the microstructure of the SLMed parts was a typical columnar structure with an oriented growth of building direction. The highest microhardness reached 198 HV0.1. Besides, the magnetic properties including Br, Hc, and P50-1 of SLMed samples decreased when the LVED ranged from 33.3 to 60.0 J/mm3 firstly and then increased while LVED further up to 93.3 J/mm3, which is related to the decrease in porosity and the increase in grain size, while the higher residual stress and microcracks presented in the samples manufactured using very high LVED. The observed evolution of magnetic properties and LVED provides a good compromise in terms of reduced porosity and crack formation for the fabrication of SLMed Fe-50wt% Ni permalloy. The theoretical mechanism in this study can offer guidance to further investigate SLMed soft magnetic alloys.