Corrosion behavior of Ni-based coating with Ni-coated TiC-reinforced particles by induction cladding in molten brass

Abstract

In order to improve the wettability of TiC-reinforced particles with Ni-based alloy and decrease electrical resistivity of TiC-reinforced particles, Ni-coated TiC particles were fabricated by electroless plating method. Further, Ni-based coatings with Ni-coated TiC-reinforced particles on the surface of H13 steel were prepared by induction cladding. The microstructure and phase compositions of the coatings were analyzed by optical microscopy, scanning electron microscopy and X-ray diffraction. The microhardness of the coatings was measured by a microhardness tester. The corrosion behaviors of the H13 substrate and Ni-based coatings with and without Ni-coated TiC-reinforced particles in molten brass were investigated. The results showed that the addition of Ni-P layer of approximately 1.2 μm thickness on TiC particles by electroless plating significantly increased cladding temperature of Ni-based coating reinforced by TiC particles, and reduced coating thickness, defects, size of the precipitated phases and microstructure inhomogeneities. The surface microhardness of the Ni-based coating with Ni-coated TiC-reinforced particles is 168% higher than that of the substrate and 17% higher than that of the Ni-based coating. The zinc in the molten brass intruded into the H13 steel and formed mixed oxides of iron, chromium and zinc in the surface layer of the substrate with the intruded oxygen. Then the mixed oxides peeled off in the mixed oxide zoneⅡof Fe and Zn adjacent to corroded surface, while the corrosive mechanism of the Ni-based coatings involves the rapid dissolution of Ni and Si of the received coatings into the molten brass and the oxidation of Si and Zn at the corrosion interface which then peeled off in the mixed oxide zone Ⅰ of Zn and Si adjacent to the coating. The addition of Ni-coated TiC-reinforced particles refined the size of carbide and boride precipitates, preventing the formation of large corrosion pits formed in the matrix phase, and effectively slowed down uneven corrosion of the Ni-based coating.