Abstract
In order to investigate the corrosion mechanism in molten aluminum alloy, NiCrBSi coating was prepared on H13 tool steel by laser-cladding. The coating mainly contained γ-(Ni, Fe), Cr7C3, Ni3B, and CrB. Floret-shaped CrB and dendritic Cr7C3 were uniformly distributed in the Ni-based solid solution matrix, with Ni-Ni3B network eutectics separated around them. The corrosion test results in molten aluminum alloy at 1073 K revealed that NiCrBSi coating exhibited excellent corrosion resistance, which was attributed to its boride-containing phase composition and microstructure. Borides can help prevent the coating surface from being wetted by liquid aluminum at the early stage of corrosion. With the prolongation of the corrosion time, molten aluminum alloy began to wet the coating surface and react with it to form a transition layer. However, the dense network structure formed by CrB hard phases and boron-rich eutectics can effectively prevent liquid aluminum from intruding into the interior part of the coating. Meanwhile, the raised borides at the interface can also slow down the reaction between aluminum and the surrounding Ni-based matrix. Thus, the corrosion rate was relatively slow and a transition layer with the thickness of 140 μm was formed after 150 h of corrosion, while the inferior coating and H13 substrate still remained intact.
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