Study On The TiN、TiN-Al₂O₃ Cermet Composite Coating By The Reaction Of Nitrogen Arc Cladding

With the development of mechanization, agricultural machinery plays an extremely important role in soil preparation, planting, harvesting and other aspects. Correct, rational and effective usage of agricultural machinery can significantly increase the production and income for agriculture. The hard soil particles often bring impact, abrasion, and corrosion to the key agricultural components through the contact soil, which easily leads to early failure. This has become the key factor affecting the working quality, cost, and efficiency. Based on the design idea of preparing TiN、TiN- Al2O3 cermet coating on the surface of the contact soil cutter of agricultural machinery, the generation mechanism of TiN had been studied, and the affect of cladding current, cladding speed, nitrogen flow, Al2O3 content to the coating microstructure, phase, microhardness,wear and corrosion resistant had been studied, meanwhile, the process parameters had been optimized.The main results are listed below:In the course of the reaction of nitrogen arc cladding, high nitrogen arc energy makes some nitrogen gas ionizing into nitrogen ions(N +, N-) and nitrogen(N), nitrogen ions and nitrogen atoms react with molten Ti to generate TiN cermet composite coating by diffusion,surge of molten pool and the electromagnetic blowing force.Coating phase consists of TiN and Fe, TiN presents dendritic, irregular granular, TiN grains and the sbustrate element form a good metallurgical bond with mutual penetration.Cladding parameters have an important influence on the coating microstructure and properties. When the current is 160 A, the speed is 3mm /s, the nitrogen gas flow is 20 L / min, the coating has high microhardness, and the microhardness is up to 1000 HV, about five times the microhardness of the sbustrate. Compared with the sbustrate, TiN cermet coating has good wear resistance.To wear resistance as a target, TiN cermet coating process parameters had been optimized: cladding current is 180 A, the nitrogen flow is 20 L / min, cladding speed is 3mm /s, tungsten diameter is ?3.2mm. TiN coating had been prepared on the sbustrate with the optimized parameters, and average microhardness of TiN coating is about 1000 HV, up to 1200 HV.Corrosion tests showed that the corrosion speed of TiN metal ceramic coating is 1/3 times that of the substrate in 3.5% Na Cl solution and 5% H2SO4 solution, compared with substrate,TiN has good corrosion resistance.Al2O3 content plays greater impact on the microstructure and properties of TiN- Al2O3 cermet coating by nitrogen arc cladding. When the Al2O3 content is 6%, the coating of the hard phase occurs discrete distribution, without obvious cracks, stomatas, holes and other defects, the microhardness is of up to 1400HV; However, as the increase of Al2O3 content by 10% and 12%, there are more stomatas, cracks and even the phenomenon of ravines on the coating surface, and microhardness lowest decresed to 600 HV.Compared with TiN coating, the highest microhardness of TiN-Al2O3 coating is increased about 200 HV, and the friction coefficient change smoothly. Corrosion tests showed that TiN coating corrosion potential is lower than TiN-Al2O3 coating in 3.5% Na Cl solution,TiN coating corrosion tendency is greater than TiN-Al2O3 coating, and in 5% H2SO4 solution, both corrosion potential is almost unanimous. But in both corrosion solution, corrosion current and corrosion rate of TiN-Al2O3 coatings are less than TiN coating, corrosion resistance of TiN-Al2O3 coatings is better than TiN coating.TiN-Al2O3 cermet composite had been prepared on the surface of deep-shovel wear resistance tests show that deep-shovel surface occurs the wear grooves paralleling to the force direction. Accelerated wear test had been implemented for welding shovel tip and cladding shovel tip in home-made abrasive wear device. The results show that the average wear amount of welding shovel tip is about 50 mg, and the average wear amount of TiN-Al2O3 coating shovel tip is about 30 mg, TiN- Al2O3 coating shovel tip manifests as good wear resistance.