Preparation Of Nano-h-BN/Ni-based Alloy Composite Coating And Related Phase Interfacial Compatibility

Solid lubrication problem is eager to be solved in high temperature service condition. As an excellent high temperature lubricant, h-BN (hexagonal boron nitride) is an ideal material in preparation of metal matrix self-lubricanting coating. This research studied on electroless nickel plating on nano-h-BN particles, and the nano-h-BN/Ni based alloy self-lubricant layers were prepared by laser cladding and HVOF(High-Velocity Oxygen Fuel) spraying separately. The shaping property, microstructure, frictional behavior and wear resistence were studied, and mechanism of nickel coated nano-h-BN improving the phase interfacial compatibility was discussed. Experiment results were analyzed with HRTEM, SEM (+EDX) and XRD.A preliminary technology that produces complex powder nano-h-BN/ Ni through electroless nickel plating using ammonia as complexing agent , hydrazine as reducing agent, CH3(CH2)11SO3Na(SDS) as dispersant agrent was researched through single factor experiment and orthogonal test. The optimized parameters of electroless nickel plating for nano-h-BN particles whose average grain size is 80nm were determined. XRD result shows that the composite powder is consist of Ni and h-BN. And h-BN was coated close by nano-scale Ni existing under HRTEM.Optimized technique was used to prepare the laser cladding metallic matrix coating. Microstructure analysis shows that: hard phase such as CrB2, CrB distributed in Ni based alloy. The addition of h-BN refined the crystal and reduces the hardness. The interfacial compatibility between h-BN and Ni-based alloy was enhanced significantly by electronless plating of Ni onto nano-h-BN powder. The composite powder containing Ni coated h-BN(h-BN(Ni)) and Ni based alloy in the results become more notable. Model was built to explain how the h-BN(Ni) improve the related phase interfacial compatibility.Ball-shaped precursor particles for HVOF spraying were prepared with composite powder by the process of ball milling, pelleting and sintering. XRD results show that h-BN exists in precursor particles. HVOF spraying layers were obtained using the precursor particles and the particles changed into flat ones and holding-on each other as layer structure. Characters of h-BN(Ni) layers such as smooth surface, little sputter, deposition and interface bonding were better than layer shaped with the original h-BN powder. And there are more h-BN lubricating phase and hard phase such as carbide and metal boride.Friction coefficients of laser cladding coatings were evaluated using a pin-on-ring friction in room and high temperature. In room temperature, the maximum decrease of friction coefficient was 0.2 after the Ni-Cr-B-Si composed with h-BN(Ni), and the number was 0.1 after adding the original h-BN powder. Wear performance was also improved by h-BN(Ni). In 400℃, friction coefficient of h-BN(Ni) coating was 0.33, and was lower than 0.38 of that of h-BN coating.