Severe erosion wear is found on valve spools, which threatens the safety and reliability of these units. The use of the plasma beam spraying surfacing method can significantly improve the corrosion resistance and sealing performance of hydraulic valve spools, reduce material waste, and reduce maintenance costs. The effects of the co-addition of CeO₂ and SiC particles on the morphology, surface cracks, microstructure, precipitated phases, and wear property of plasma-beam-sprayed Fe55-based coatings on 1025 steel were investigated using OM, EDS, ultra-deep field microscopy, and a wet sand rubber wheel friction tester, respectively. The dendrite exhibited a directional growth pattern perpendicular to the substrate and the transitional states of the microstructure with the co-addition of CeO₂ and SiC particles. CeO₂ or SiC reduced the liquid phase diffusion coefficient D_L of Cr and C and resulted in a decrease in the G/R ratio. The dendrites changed into equiaxed grains. The main phase composition of the Fe55 welding layer was Cr₇C₃, γ-Fe. The martensite in the surfacing layer and the carbides formed Cr₇C₃, which can improve the hardness of the surfacing layer. The grain boundaries consisted mainly of a reticular eutectic structure. The uniform distribution of the Cr₇C₃ hard phase in the Fe55+1.5 wt% SiC+0.01 wt% CeO₂ resulted in a uniformly worn surface. The sub-wear mechanisms during the friction process were micro-ploughing and micro-cutting. The hardness and toughness of Fe55+1.5 wt% SiC+0.01 wt% CeO₂ were well-matched, avoiding excessive micro-cutting and microplastic deformation. A low content of CeO₂ could lead to the formation of equiaxed grain and effectively improve the uniformity of the microstructure. The wear-resistant layer of Fe55+1.5 wt% SiC+0.01 wt% CeO₂ can effectively improve the service life and long-term sealing performance of the valve spools.

The effects of co-addition CeO2 and SiC particles on the morphology, surface cracks, microstructure, precipitated phases and wear property of plasma beam spraying Fe55-based coatings on 1025 steel were investigated by optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDS), ultra-deep field microscope and wet sand rubber wheel friction tester, respectively. The results showed that the dendrite exhibited a directional growth pattern perpendicular to the substrate and the transitional states of microstructure with the co-addition CeO2 and SiC particles. With addition of CeO2 or SiC affected the flowability of molten steel at macro level, leading to a reduction in the liquid phase diffusion coefficient DL of Cr and C and resulted in a decrease in the G/R ratio. The dendrites changed into equiaxed grains. The main phase composition of Fe55 welding layer is Cr7C3, γ-Fe. The grain boundaries consisted mainly of a reticular eutectic structure. The worn-out uniformly surface of the Fe55+1.5 wt% SiC+0.01wt% CeO2 with Ra was 0.28 μm was smoother than that of other samples. The sub-wear mechanisms during the friction process were microploughing and microcutting. The hardness and toughness of Fe55+1.5 wt% SiC+0.01wt% CeO2 were well-matched, avoiding excessive microcutting and microplastic deformation.

Valve leakage mainly comes from worn sealing surfaces caused by abrasive particles. This study uses plasma beam spraying to create Fe55 alloy coatings with CeO₂ and TiN added to improve microstructure and wear resistance. Five coatings were prepared: Fe55 with 0.02% CeO₂ (FC2), 0.04% CeO₂ (FC4), 1% TiN (FT1), 2% TiN (FT2), and 2% TiN/0.02% CeO₂ (FC2T2). These coatings were tested for wear and erosion using wet sand and slurry experiments. Results showed that FC2T2 had the most uniform microstructure with fully equiaxed grains (20.32 μm size) and no columnar grains. This was due to CeO₂ and TiN co-working effect: CeO₂ was adsorbed onto TiN surfaces, reducing TiN decomposition and acting as nucleation sites. The FC2T2 coating also showed the highest hardness uniformity (no large changes with depth) and the lowest surface roughness after wear (41% lower than pure Fe55). In wear tests, FC2T2’s Cr₇C₃ hard phases blocked abrasive cutting, while the γ-Fe matrix prevented Cr₇C₃ from breaking off. Erosion tests confirmed FC2T2’s superior performance, as its uniform structure limited deep grooves. Adding both CeO₂ and TiN improved wear resistance by providing a balanced microstructure, reducing leakage risks in valve sealing surfaces.

A weak transverse static magnetic field was applied during PTA cladding of Inconel 625 to control solidification microstructure and solute segregation. At 15 mT, the continuous coarse columnar growth was suppressed and local Nb/Mo enrichment was mitigated. The area-weighted mean equivalent grain diameter decreased from 348.2 μm to 243.2 μm, the maximum pole density from 23.02 m.r.d. to 13.52 m.r.d., and the mean aspect ratio from 4.18 to 2.33, indicating a columnar-to-equiaxed transition and weakened texture. This refined and homogenized microstructure improved corrosion resistance (Rct: 452→691 kΩ·cm²) and wear resistance (specific wear rate ↓58.2%), while microhardness increased only modestly a disproportionality suggesting that the enhanced wear resistance was governed by microstructural homogenization rather than hardening. The magnetic field acts through two mechanisms: Lorentz-force-driven macroscale melt flow restructuring and thermoelectromagnetic micro-convection at the solid–liquid interface, which together disrupt the thermal-solutal boundary layer and suppress directional columnar growth.