Study On Microstructures And Properties Of Ti(C,N) And WC-Ni Based Cermet Coatings Prepared By Electrospark Deposition

Cermet coating is widely used in the field of die steel surface repair and strengthening due to its advantages of high hardness,high wear resistance and low cost.At present,there are many technologies that can be used to prepare cermet coating.Electrospark deposition has unique advantages in the preparation of cermet coating because the technology has the characteristics of small heat affected area,good metallurgical combination between coating and substrate,and strong adaptability to the operating environment.In this paper,Ti（C,N）and WC-Ni cermet coatings were prepared on H13 steel by electrospark deposition.The influence of process parameters on the thickness and surface roughness of the coatings was analyzed.The microstructure,microhardness and friction and wear properties of the coatings were studied.At the same time,Ni rod and Mo rod were used as electrodes to prepare cermet composite coatings with Ni and Mo as transition layers on the surface of the substrate.Ti（C,N）-based cermet coating was prepared on H13 steel surface.The optimized process parameters were:deposition power 1000W,output voltage 60V,discharge frequency 700Hz,specific deposition time 5min·cm^-2.The thickness of Ti（C,N）-based cermet coating was 30-40μm,and the surface roughness Ra was about 2μm.The main phases in the coating include TiC_0.7N_0.3、MoC、Ni₁₇W₃ and Co_5.47N,and the alloy phases Ni-Cr-Co-Mo、Fe₃Ni₂ and Fe_0.975Ti_0.025.The coating surface was covered by micro deposition points with diameters ranging from 2μm to 15μm.The cross-section structure was uniform and continuous.The coating consists of ceramic hard phase,gray ring phase and bonding phase,in which the average particle size of ceramic phase was about 0.6μm.The maximum microhardness of Ti（C,N）-based cermet coating was about 1039HV,which was 4 times higher than that of H13steel.The friction coefficients were 0.49（5N）and 0.54（8N）,respectively,which was about35%lower than that of H13 steel,the wear weght loss of the coating was about 0.7mg（5N）and 1.1mg（8N）within 30min,which is about 43%lower than that of the substrate,the coating showed excellent wear resistance and anti-friction property.WC-Ni based cermet coating was prepared on H13 steel.The optimized process parameters were:output voltage 60V,deposition power 800W,discharge frequency 700Hz,specific deposition time 4 min·cm^-2.The average thickness of the coating was about 35³7μm,and the surface roughness Ra was 2².5μm.The main phases in WC-Ni based cermet coating were W₂C,WC,WC_1-x,Ni₄W and Fe₃W₃C.The surface of the coating was made up of sputtered deposition spots with a diameter of more than 300μm.The coating cross section showed obvious delamination.WC hard ceramic phase showed diffuse distribution and was wrapped by the adhesive phase.The overall microstructure was uniform and dense,with only a few pores and cracks.The maximum microhardness of WC-Ni based cermet coating was about 816HV,which was three times that of H13 steel substrate.The average friction coefficients of WC-Ni based cermet coating were 0.541（5N）and 0.512（8N）,respectively,which was about 28%lower than that of the substrate,the wear weght loss of the coating was about 0.6mg（5N）and 1.5mg（8N）within 30min,which was about 40%lower than that of the substrate,the coating showed excellent wear resistance and anti-friction property.Four kinds of cermet composite coatings with Ni and Mo as transition layers were prepared by two-step deposition method with Ni and Mo electrodes.The introduction of Ni transition layer did not change the phase composition of the coating,but Fe_0.875Mo_0.125 and Fe_9.7Mo_0.3 alloy phases were formed in Mo/Ti（C,N）and Mo/WC-Ni cermet composite coating with Mo as the transition layer.The average thickness of Ni/Ti（C,N）cermet composite coating was about 31μm,the maximum microhardness of composite coating was 1420HV,and the average friction coefficients were 0.607（5N）and 0.453（8N）respectively,the wear weight loss was about 0.6mg（5N）and 1.3mg（8N）.The average thickness of Mo/Ti（C,N）cermet composite coating was 38μm;the maximum microhardness of the coating is 1372HV,and the average friction coefficients were 0.563（5N）and 0.428（8N）,respectively,the wear weight loss was about 0.3mg（5N）and 0.8mg（8N）.The cross-section microstructure of the two Ti（C,N）cermet composite coatings were continuous and dense,with a small number of cracks.Compared with the single coating,they showed higher hardness and better wear resistance.The average thickness of Ni/WC-Ni cermet composite coating was about 41μm.The microhardness of the coating could reach up to 972HV,and the average friction coefficients of composite coating were 0.44（5N）and 0.61（8N）,the wear weight loss was about 0.5mg（5N）and 1.4mg（8N）.The average thickness of Mo/WC-Ni cermet composite coating was about 43μm.The microhardness of the coating could reach up to 1130HV and the average friction coefficients of the coating were 0.34（5N）and 0.53（8N）,the wear weight loss was about 0.3mg（5N）and 1.8mg（8N）The microstructure of the two WC-Ni cermet composite coatings were multi-layer composite structure,with only a few hole defects.Compared with the matrix and single coating,they showed better wear resistance and antifriction property.