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Galvanized steel materials is one of the primary means of corrosion, but the molten zinc or zinc-aluminum alloy for galvanizing member has a strong corrosive, such as hot-dip galvanizing pot sink roll, stabilizing roll, etc. galvanized parts, often corrosion by molten premature failure. Molten zinc in addition to being a member other than etching, but also by the dross in the melt and other hard abrasive particles, so the working conditions are very bad. Because of thermal sprayed ceramic coatings with good wear resistance, corrosion resistance and hot-dip galvanizing commonly used for the protection member, but the thermal sprayed ceramic coatings often led to its intrinsic brittleness spalling failure, thereby limiting its redu Zinc parts protection application. To solve this problem, the present study was to analyze the current domestic and international resistance to molten zinc or zinc-aluminum alloy corrosion protection technology research status, combined with molten zinc or zinc-aluminum alloy melt the material corrosion mechanism, developed a new type of non-metallic binder phase based ternary boride ceramic coating, and the coating contains a certain amount of amorphous, nanocrystalline organization is expected to improve the use of nanocrystalline material strength and toughness characteristics to solve the problem of ordinary ceramic coating brittleness, while addressing the cermet coating is not corrosion problems. Therefore, this study has a high application value and theoretical significance. In this paper, technical route is as follows: First, using the CALPHAD (Calculation of Phase Diagram) technique for the study of Co-Mo-B ternary phase equilibrium thermodynamic calculations carried out, in order to guide the initial powder composition ratio. The initial powder composition ratio determined by wet milling, spray drying, high temperature sintering and the screening process, successfully prepared with a high bulk density and good fluidity, spherical or near spherical shape, average particle size distribution of about 32μm ternary boride-based ceramic powders. Using supersonic flame (HVOF) spraying technology in 316L stainless steel substrate prepared in the ternary boride base ceramic coating, using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), differential scanning calorimetry Calorimetry (DSC), differential thermal analysis (DTA), thermal expansion, micro-indentation and mercury intrusion detection and other analytical tools, the organizational structure of the coating, mechanical and physical properties were studied, and the coating amorphous and nanocrystalline formation of a thermodynamic analysis. Finally studied in molten zinc-aluminum coating (Al-43.5Zn%-1.5Si) fluid corrosion and corrosion-resistant mechanism. The main contents and conclusions are as follows: initial powder composition ratio is approximately: Co: 22.92wt.%, MoB: 59.08wt.%, CrB: 18wt.%. Borides-Co composite slurry is shear thinning and pseudoplastic fluid characteristics, the viscosity increases as the shear rate decreases; when the dispersing agent, a binder content of the solid phase content of 0.5wt.%, And 2.4 wt.%, the total solid content of the slurry mass 45wt.%, the composite slurry maintaining low viscosity and good dispersion stability, suitable for subsequent spray granulation. Spray drying the optimum temperature range of 300-325 ℃, in this temperature range can be maximum 73% of dry collection, and most particles are spherical shape, better mobility; powder by thermal analysis to determine the optimal agglomeration The sintering temperature is about 1290 ℃ so, the test at this temperature for sintering the powder obtained contains CoMoB CoMo2B2 and two-phase, and two yuan borides MoB, CrB, found no other oxide phases, and the internal powder showed a porous structure, adhesion phenomenon does not occur between the particles. HVOF spray three yuan boride-based ceramics coating structure is dense, pore distribution, found no cracks or large number of unmelted particles. Coating porosity of about 6.38%, an average pore diameter of about 0.16μm, the coating of the pore size distribution was bimodal distribution. Detected by XRD analysis in the coating phase, there are four main crystalline phase CoMoB, CoMo2B2, MoB, CrB and amorphous phases, the percentage content of each phase were CoMo2B2: 45.8wt.%, CoMoB: 19.7wt .%, MoB: 2.3wt.%, CrB: 16.4wt.%, amorphous: 15.8wt.%. Nanocrystalline size of less than 10nm. Amorphous coating spray droplet formation is due to the rapid cooling and a suitable powder composition; due to subsequent accumulation of molten droplets have formed a coating on the annealing effect produced, nanocrystalline to homogeneous nucleation and heterogeneous nucleation means within the amorphous and amorphous respectively formed at the interface with the boride. Ternary Boride-based ceramic coating exhibited a higher hardness, elastic modulus and fracture toughness, thanks to the coating of amorphous, nanocrystalline and the presence of high hardness boride. Coating hardness, elastic modulus and fracture toughness exhibited anisotropy, Weibull distribution shows: the coating surface and cross-sectional microhardness showed bimodal distribution. The bonding strength with increasing coating thickness gradually decreases. Ternary Boride-based ceramic coating, the adhesive layer and the thermal expansion coefficient of the substrate was approximately 8.9 × 10 -6 / K, 14.3 × 10 -6 / K, 17.2 × 10 -6 / K. Three yuan boride-based ceramic coating liquid aluminum in molten zinc etching experiments show that the coating has excellent corrosion resistance, in the life of the melt close to 600h, far higher than the WC-Co (WC), low Carbon WC-Co (LW) coating. No heat treatment melt and ceramic coating (TB) is superior to the wettability and heat melt ceramic coating (HTTB), which is contained in the coating layer of amorphous TB caused. Erosion in the melt after 50h, TB partial surface coating thickness of about 20μm or so erosion area while HTTB coating surface is not etched signs; etching after 600h, TB coating basically no erosion area change, HTTB coating erosion phenomenon is still not found. This is because the coating layer contains amorphous structure TB, although generally considered amorphous metal is a combination of keys, but in a thermodynamically metastable atoms which is far higher than the activity of crystalline alloys. Therefore, in the wetting process, the amorphous alloy is easy to etch the atomic diffusion into the melt; coating at about 600 ℃ molten Zn-Al etching solution after a certain time, the coating gradually amorphous into a crystal structure, erosion of the coating melt it basically stopped. After etching the coating TB 600h, failure occurred within the coating form of a plurality of parallel on the ceramic layer / adhesive layer interface, transverse cracks, and inner adhesive layer and an adhesive layer / substrate interface without occurrence of cracks, this part The reason is due to the rotation of the specimen during etching of aluminum and zinc dross hard particle collisions caused by mechanical damage, another important reason is due to the thermal expansion coefficient mismatch caused by thermal stress damage.
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