| 45 steel is a common high-quality carbon structural steel,which is often used in the manufacture of connecting rods,bolts,gears,shafts and other parts under alternating loads.Due to the low surface hardness and poor wear resistance of 45 steel,the parts are prone to failure under complex working conditions.Plasma cladding technology can be used to improve its surface properties and prolong the service life of the workpiece.In order to improve the wear resistance and corrosion resistance of the 45 steel surface,three kinds of coatings: CoCrNi coating,CoCrNi+TiC coating and CoCrNi+Al coating,were deposited on the surface of 45 steel by plasma cladding in the paper.The microstructure,Vickers hardness,friction and wear properties and corrosion resistance of the coatings were studied.In order to further improve the microstructure and properties of the coating,the effects of different heat treatment processes on the microstructure and properties of CoCrNi+Al coating were also studied.The CoCrNi coating prepared under the optimized process parameters has a good metallurgical combination with 45 steel.The coating is mainly composed of a single FCC(Fe,Ni)solid solution phase.The average hardness is 196 HV0.3.The average friction coefficient and the amount of wear are 0.6 and 23.2 mg,while the self-corrosion potential and the current density are-596.33 mV and 1.58×10-4 mA/cm2,respectively.The hardness and wear resistance are not as good as 45 steel,and the corrosion resistance is better than 45 steel.The hardness and wear resistance of the CoCrNi+TiC coating have been significantly improved.The research results show that the microstructure can be refined by adding ceramic particles TiC.When the content of TiC is 25%,the comprehensive properties of the coating are better.The phase composition is FCC phase and TiC phase.The coating hardness is 401 HV0.3,which is about 2 times higher than that of the substrate.The wear amount is 2.5 mg,and the wear resistance is significantly improved.The wear mechanism is mainly abrasive wear,the self-corrosion potential is-479.08 m V.The current density is 1.16×10-4 m A/cm2,and its corrosion resistance is equivalent to that of CoCrNi coating.With the increase of Al content,the phase structure of CoCrNi+Al coating changes from FCC phase to BCC phase.Due to the larger Al atomic radius,the solid solution strengthening effect is obvious.The average hardness of the coating increases from 196 HV0.3 to 650 HV0.3 when 20% Al is added.The friction factor is 0.347,and the wear resistance of the CoCrNi+Al coating is better.Excessive addition of Al will lead to the decrease of corrosion resistance.When the Al content is 15%,the corrosion resistance is the best.The CoCrNi+Al coating is annealed at 300 ?,500 ?,700 ?,and the holding time is 30 min.When the Al content is 5%,the coating phase structure hardly changes after annealing,but the coating structure is obviously refined and the coating hardness does not change significantly.When the amount of Al is 15%,the intensity of the(110)BCC diffraction peak of the coating increases with the increase of the heat treatment temperature.When the annealing temperature is 700 ?,the coating is composed of a single BCC phase.The hardness of the coating decreases as the annealing temperature increases.When the Al content is 20% and the annealing temperature is 300 ?,the microstructure transforms into dendrites.Due to the lower heat treatment temperature,the atom diffusion ability is weak and the fine second phase is precipitated in the grains.The atom diffusion ability is enhanced at the annealing temperature of 500 ?,the precipitates mainly appear between the dendrites.When the annealing temperature is 700 ?,there are more larger size precipitation between the dendrites.The hardness of the coating increases as the annealing temperature increases. |
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