In-situ reactive fabrication and effect of phosphorus on microstructure evolution of Ni/Ni–Al intermetallic composite coating by laser cladding

• Ni–Al intermetallic composite coating was in-situ reactive fabricated by laser cladding.
• Phosphorus and Y2O3 contributing to improving microstructure evolution of coating
• The synchronous formation of Ni3Al and Ni3P led to the skeletal microstructure.

The objective of the study was in-situ reactive fabrication of Ni/Ni–Al intermetallic composite coating by laser cladding with preplaced nickel and aluminum mixed powder on nickel alloy substrate. The phase composition and improvement of microstructure evolution of Ni/Ni–Al intermetallic composite coating were investigated by X-ray diffraction, scanning electron microscopy, and energy dispersive spectrometer. It was shown that the Ni/Ni–Al intermetallic composite coating was composed of γ-Ni, Ni3Al, and NiAl and the addition of phosphorus had a crucial influence on microstructure evolution of coating. Interfacial cellular microstructure was refined by introducing phosphorus element and the preferred growth was weakened by the fine Ni3Al + Ni3P dual-phase microstructure. The exothermic effect of forming Ni–Al intermetallic compounds (IMCs) improved the fluidity of liquid pool and homogenized the composition of molten pool. The synchronous formation of Ni3Al and Ni3P led to forming skeletal microstructure. Microhardness of coating is about 6 times higher than that of substrate. The addition of phosphorus element has a contribution to improving microhardness (up to 750 HV0.2) while the microhardness is not increased but homogenized by addition of Y2O3.

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