| In order to improve the agricultural touching soil cutter and ploughshare which tend to wear out easily, break down frequently, have high costs and short service scope, the paper has taken a process of cladding ceramic coating on the metal surface as its object.The method adopted is as following: a kind of PTA(Plasma Transferred Arc) cladding technology with the use of atmospheric pressure reactive to synthesize in-situ hard phase Ti(C,N)-WC, Al2O3-Ti(C,N) particles to form metal ceramic composite coating on Q235 A plain carbon steel surface. Under the conditions of regulating and controlling the process parameters, raw powder of mass ratio and different formulations are tested to study the organization structure, wear resistance and corrosion resistance of the Ti(C,N)/metal composite coating. This paper studies the formation mechanism, applying orthogonal test method to optimize plasma cladding process parameters, with the intention of providing reference for the surface strengthening of agricultural materials with applying composite coating containing Ti(C,N).The results demonstrate that the Ti(C,N)-WC/Ni60 A based metal ceramic composite coating with Ti N powder as solid nitrogen source and through the reactive plasma cladding technology, was synthesized in-situ. The Ti(C,N)-WC/Ni60 A composite coating metallurgical combined with the substrate. Polygonal flake WC distributed in the cladding coating surface and the core-ring structure dispersed among the adhesive phase of the subsurface. The raw material powder composition and its content had such influences on coating quality and organizational structure as the followings. With the increase of Ni60 A, the number of the hard phase particles decreased; the core-ring structure was not complete; the distribution of the hard phase particles tended to be uneven and disappeared and the hardness of the coating decreased. Besides, the ring thickness of Surrounding Structure phase reduced or ring was not complete; the hard phase grain was refined gradually; the core-ring structure became incomplete and porosity and cracks in coating increased. Consequently, the coating produces crisp phase Ni3 Ti, leading to the hardness decrease. In a certain range when WC content was 12%, the micro-hardness, degree of wearing out and corrosion resistance of coating were optimal, the increase of WC content effectively improved the wettability of the hard phase and binder phase, inhibited the hard phase grain growth and improved the micro-hardness.The Ti-C-N-W-Fe-Ni system has been analyzed by thermodynamics with the result that under the condition that the free energy Ti(C,N) particles is the minimum, and the reaction products are the most stable it is feasible to form Ti(C,N)-WC hard phase particles.The kinetics having been analyzed with the metallurgy reaction kinetics model and thecharacteristic equation, was found the reaction rate of Ti C?Ti(C,N) by reducing the content of Ni60 A, improving the cladding temperature, decreasing the Ti-rich intermediate layer thickness, and refining the carbon particle size. Distribution and diffusion distance of the hard phase particles are related to the system absolute temperature, cladding time, the particle diameter and the metal liquid viscosity coefficient.The highest hardness value of the coatings was up to HV0.52040, and the average hardness was HV0.51750, about 7.2 times of the substrate. When the coatings was in wear stable period, the mean dry sliding friction coefficient was 0.38, and the wear resistance of the composite coating was 6 times higher than 65 Mn steel, and 16 times higher than Q235 A substrate. The plasma cladding process parameters were optimized by wear loss as the investigation target, and the best combination of the process parameters was A3B2C3D3E2,coatings had better corrosion resistance behavior than the substrate. In 5% H2SO4 solution,the corrosion rate of the coating with WC content of 12% was 1/9 of Q235 A, while in3.5% Na Cl solution was 1/4 of Q235 A.Using Ti N powder as solid nitrogen source, the heat released from the exothermic reaction of termite as an internal heat source, and plasma arc column as an external heat source, Al2O3-Ti(C,N)(AT composite materials) was synthesized in-situ, and the coating and the substrate was metallurgical combined. The coating was composed of reticular structure, nested structure and spherical structure. The hard phase Al2O3 and Ti(C,N) and Fe-Ni binding phase were mutual inclusion between themselves body, nested within each other, constituting the spatial reticulate structure. The highest hardness value of the coatings was up to HV0.52160, and the average hardness was HV0.51870, and about 7.7times of Q235 A steel substrate. The friction coefficient of AT composite coating was about0.372, and the wear resistance of the AT composite coating was 7 times higher than 65 Mn steel, and 17 times higher than Q235 A substrate surface. In acid and sodium chloride salt solution environment, the corrosion rates of AT coating were respectively 1/10 and 1/5 of Q235 A. The corrosion resistance of the AT composite coating was better than Q235 A.Using the low cost carbon nitrogen compounds as the precursor of carbon and nitrogen and pre-preparing high nitrogen content of carbon nitride powder, with g-C3N4 powder as carbon and nitrogen source, the Ti(C,N) was synthesized in-situ, and the coating and the substrate was metallurgical combined. The coating zone was mainly composed of spherical core-ring structure including Ti(C,N) and white edges flake WC as hard phase,and Fe-Ni alloy as the binding phase. The highest hardness value of the coatings was up to HV0.51830, and the average hardness of the coating was HV0.51700, and about 7 times of the Q235 A. The friction coefficient of the composite coating was about 0.42, the wear resistance was 4.7 times higher than 65 Mn steel, and was 11.6 times higher than Q235A;In acid and sodium chloride salt solution environment, the corrosion rates of composite coating were respectively 1/7 and 2/7 of Q235 A. The melamine as the precursor of carbon and nitrogen prepared the composite coating which had better corrosion resistance than the Q235 A substrate. |
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