Laser powder fusing as an additive manufacturing process to create the ferromagnetic coatings on the basis of Fe and Sm powders on stainless steel substrate

Abstract

A robotic laser technological complex has been used for the laser powder fusing (LPF) of samarium (Sm) and iron (Fe) powders on stainless steel (SS) substrate in argon flow conditions for the creation of thick (1.0–1.5 mm) ferromagnetic coatings. The formation of Fe–Sm–Ni–Cr and Fe–Cr–Sm alloys was demonstrated on SS substrate due to intensive diffusion of Fe, Cr and Ni atoms from the substrate. A magnetic field (0.2 T) during LPF on the SS substrate resulted in crystallisation of single grains (5–20 microns) of the Fe–Cr–Sm alloy with mutually perpendicular orientation, which were embedded in the Sm–Fe–Ni–Cr alloy matrix and formed a mesh structure in the fused layer. When the additional magnetic field was absent during LPF the larger part of Sm atoms were located in near-surface sample area and around elongated grains, as well as in small grains of spherical form, but dissolution of Sm was blocked in elongated grains. The fused layers from Sm and Fe powders on SS substrates with and without magnetic field had a low coercivity (20–100 Oe), near zero residual magnetisation and high saturation magnetisation (110–112 emu/g) at 300 K. The maximum coercivity (100 Oe) was observed for coating fused with magnetic field, corresponding to mutually perpendicular orientation of ferromagnetic Fe–Cr–Sm grains. The cooling of samples to 4 K resulted in magnetic ordering with a Curie temperature of 50 K and with small changes in coercivity.