Magnetic Properties of Fe-Ni-Cr Alloy Coatings Processed via High-Velocity Oxygen-Fuel Spraying

In this work, soft magnetic coatings were fabricated from Fe-Ni-Cr (1J38) alloy powders via high-velocity oxygen-fuel (HVOF) spraying. The microstructural features and intrinsic magnetic properties were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and a background signal stripping algorithm. Furthermore, the microstructural defects and magnetic degradation characteristics of coatings with varying thicknesses were comparatively analyzed. The results indicate that while the HVOF deposits exhibit exceptional density, the rapid quenching process inevitably induces oxygen-rich inter-splat boundary networks and residual stresses within the coatings. XRD analysis reveals no significant macroscopic oxidation or phase transformation during deposition, demonstrating a high-fidelity retention of the original face-centered cubic (FCC) lattice structure of the feedstock alloy. Magnetic measurements, upon the precise elimination of substrate background interference, reveal a distinct wasp-waisted magnetization distortion at low magnetic fields. This phenomenon can be attributed to the asynchronous magnetization response between the easily reversed, unoxidized soft-magnetic splat cores and the high-barrier boundary pinning networks (composed of inter-splat oxide interlayers and localized high-stress concentrations) within the coating. Compared to the thicker deposits (0.5 mm), the thinner coatings (0.3 mm) exhibit superior magnetic performance, characterized by a lower intrinsic coercivity. This degradation in thicker coatings is ascribed to the substantial accumulation of macroscopic residual stresses during deposition, which exert a stronger pinning effect on magnetic domain wall motion.