Research Of Preparation And Performance On Nickel Base Al₂O₃-TiB₂ Composite Coatings Used Fly Ash As Composite Activating Flux By Activating-argon Arc Cladding Method

The high-aluminum fly ash was used as main raw material to ascertain the best parameters of argon arc welding process on the substrate of Q235 steel by orthogonal design method. Four kinds of materials with the best comprehensive effect were choosed as the basic constituents of the composite activating flux based on the effect of single constituents, such as oxide, haloidon, element and rare earth as well, on increasing the weld penetration and the efficient and environment friendly composite activating flux from fly ash were prepared by uniform design method. The composite activating flux were applied to argon arc cladding progress further and the nickel-based Al₂O₃-TiB₂ ceramic coatings were prepared on the substrate of Q235 steel by activating-argon arc cladding. The structure and properties of activating composite coatings were measured by metallographic microscope, scanning electron microscope, x-ray diffractometer, microhardness tester, grain-abrasion testing machine and erosion wear testing machine, and those were analysed comparatively with conventional composite coatings.The results show that the optimum formula of fly ash composite activating flux, whose radio of high-aluminum fly ash, SiO₂, B₂O₃, Ti and La₂O₃ is 60%,13.68%, 25.44%,0.88% and 5%, could achieve complete penetration of the 6mm thick Q235 steel all at once and its depth-to-width ratio reaches 0.75. The optimum formula of cladding materials is 60%Ni60A-16%Al2O3-24%（Al-TiO₂-B₂O₃）-5%（Na₂B₄O₇·10H₂O）. The bond structure between composite coatings and the matrix is metallurgical combination and there are no defects such as crack, pores and inclusions in the interface. The main hard phases of composite coatings are Al₂O₃, TiB₂ and Fe₂B, whereas there are Fe₁.7Al₄Si,3Al₂O₃·2SiO₂ and Ni₃Si phases in the activating composite coatings. The max microhardness of conventional composite coatings and activating composite coatings reaches 771.9HV0.1 and 946.9HV0.1 and are controlled by 4.82 times and 4.91 times respectively. The abrasive wear performance are controlled by 6.96-8.29 times and 7.05-10.65 times and the static immersion corrosion performance are 2.51-3.55 times and 2.98-4.14 times of the matrix. The erosive wear performance are improved to 2.82-5.50 times and 3.49-6.11 times at different speeds, concentrations and media.