Abstract
The wear failure of automotive engine cylinder was increasingly widespread attention by people. This article analyzes the wear failure principle of the engine cylinder wall and summarize the requirements for the performance of the engine cylinder inner surface.Based on this we identified the materials applicable to the preparation of the cylinder wall coating and produced four materials FeCrBSi, Ni60, Ni60-WC,Ni60-WC-Mo coating on Q235 Steel through flame remelting after plasma spraying. This article analyzed the performance improvement after several coating through remelting.This paper studied the phase composition of the coating using scanning electron microscopy and X-ray diffraction,and made the text to the bonding strength, hardness,porosity and friction performance.
The experimental results and analysis show:The organizationsof plasma sprayed coatings show the layered superimposed structure of the flat particles which contain cracks and holes. The sprayed layer structure is relatively loose and internal microhardness uneven ,this lead to the hardness decreases at loose tissue.The binding force between unmelted tungsten carbide and the surrounding matrix metal is not strong ,this lead to unmelted tungsten carbide come off easily under conditions of high stress abrasion.The hard phase of Ni60 and Ni60 coating primarily of chromium boride and carbide. The Ni60-WC and Ni60-WC-Mo coating increased the hard phase WC and Mo2C.
WC added significantly increase the hardness of the coating. The binding between the coating and the substrate to the mechanical coupling.The cracks and pores in coating disappeared and the organizational structure is dense and the hard phase uniformly distributed in the remelting coating. The unmelted WC particles spread fully around with the metal element diffusion and no hard phase sheddingfrom the base body when when frictioning in the remelting coating of Ni-WC.Inremelting process WC decomposition occurs, the generated W2C hardness is extremely high. The addition of Mo will improve the bonding strength of the nickel-based tungsten carbide, to reduce the coefficient of friction of the coating.The combination which between the layer and the substrate is metallurgical bond is very strong.The hardness of coating which remelting was increasedand within the coating uniform hardness distribution, and the hardness distribution uniform within the coating. The microhardness of Ni60-WC-Mo coating had the biggest increasing ,which increased by about 1.8 times, which is about 1.4 times Ni60 coating and 2 times FeCrBSi coating under the same conditions. The wear resistance of Ni60-WC-Mo coating after remelting haver an increase of nearly three times than the original coating, which is about 2.5 times Ni60 coating and 4 times FeCrBSi coating under the same conditions.
Key Words: engine cylinder,plasma spraying,remelting,microstructure,coating property
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