Effect of B4C content and particle sizes on the laser cladded B4C/Inconel 625 composite coatings: Process, microstructure and corrosion property

The B4C/Inconel 625 composite coatings were successfully prepared on 20 pipeline steel by laser cladding, in which B4C ceramic was selected as reinforcement phase to improve the microstructure and corrosion property of Inconel 625 coating. The laser cladding parameters were optimized and the effect of B4C content and B4C particle sizes on the microstructure and properties of B4C/Inconel 625 composite coatings were studied in detail. With increasing liner energy density and decreasing powder feeding speed, the crack ratio of the composite coatings reduces. NiB phase forms due to the in-situ reaction of B4C with Ni element in Inconel 625, and a thin layer of planar crystal also forms at the coating/substrate interface. As the addition of B4C content ranged 5wt.%∼10wt.% and the particle sizes ranged 10μm∼60μm, the quantities of equiaxed crystals increase obviously and the coarse columnar crystals are also refined, which contributes to the improved microhardness and corrosion resistance of the B4C/Inconel 625 composite coatings. When the B4C content is 10wt.% and particle size is 10μm, the maximum microhardness of the composite coating is about 567HV0.2, which is 241.2% to that of Inconel 625 coating. The optimal corrosion resistance of B4C/Inconel 625 composite coatings is obtained when the B4C content is 5wt.% and particle size is 60μm.