Experimental Study On Laser Cladding Of WC Reinforced Ni/Co Composite Cladding On The Surface Of H13 Steel

The surface of H13 steel?4Cr5MoSiV1?mold is prone to suffering from wearing,thermal fatigue,erosion and other failures during service,which affect production efficiency.To improve its surface performance,Co-based and Ni-based cladding layers were prepared on the surface of H13 steel samples by laser cladding technology,and the comprehensive performance of cladding layer was improved by adding WC hard phase,which would be significant for extending the service life of H13 steel,reducing the cost of mold manufacturing and saving precious metals.In this thesis,Co50 and Ni60A alloy powders were selected as the cladding materials,WC was used as the reinforcement phase,WC/Co-based and WC/Ni-based composite cladding were prepared on the surface of H13 steel by using semiconductor laser and synchronous powder feeding laser cladding equipment.This thesis mainly studied the preparation process of Co-based and Ni-based coating,the effect of WC addition on the microstructure,and properties of cobalt-based and nickel-based cladding layers.OM,XRD,SEM,EDS and other analytical methods were used to analyze the coating microscopy,structure and phase composition.The coating performance was tested by microhardness measurement,wear test and static oxidation method.The results show that:1)The optimized process parameters of Co-based cladding layer preparation are laser power 1200 W,scanning speed 7 mm/s,and relative powder feed rate 17 g/min.2)The best process parameters of Ni-based cladding layer are laser power 1000 W,scanning speed 6 mm/s,and relative powder feeding rate 15 g/min.40%lap rate and 5 L/min carrier gas flow rate were used to prepare multiple lap cladding layers.The microstructures of the Co50 cladding layer from the interface to the surface layer are plane crystal,coarse columnar crystal,dendrite,fine non-directional dendrite,and a small amount of equiaxed crystal.As the amount of WC added increases,the dendrite structure of the cladding layer is gradually refined.The phase of Co50cladding layer is composed of?-Co solid solution,M₂₃C₆,Cr₇C₃,Fe Ni₃ and Co₃W.After adding 5%WC,CCo₂W4 and W₂C phases appear in the cladding layer.When the amount of WC is 10%and 15%,the cladding layers consisting of the same phases,which are?-Co solid solution,M₂₃C₆,Cr₇C₃,Fe Ni₃,CCo₂W₄,W₂C,and WC.The microstructure of the Ni60A cladding layer tends to be gradually refined from the bottom to the top.With the increase in the dosage of hard phase?WC?added,the short columnar and island-like structures in the cladding layers continue to thicken.The Ni60A cladding layer is composed of?-?Ni,Fe?,Fe Ni₃,Ni_2.9Cr_0.7Fe_0.36,Cr₅B₃,and Cr₂₃C₆.The cladding layer with 5%WC is more Cr₃C₂ and W₂C phases than the samples without addition.The phase composition of the cladding layer with 10%and15%Ni/WC are more Cr₃C₂,W₂C,and WC phases than the samples without WC.With the increase of WC additive amount,the microhardness and wear resistance of Co-based and Ni-based composite cladding layer were gradually improved.The microhardness of Co50-15%WC was 732.6HV_0.2,and Ni60A-15%WC was1116.2HV_0.2.The morphology of friction and wear showed that for Co-based cladding layer,the main wear mechanism was adhesive wear and plastic deformation,and the worst wear resistance.With the addition of WC,the wear mechanism was abrasive wear and Co50-15%WC has the best wear resistance.For the Ni-based cladding layer,the main wear is abrasive wear.With the increase of WC additive amount,the furrow in the wear morphology was gradually reduced,shallower and narrower,the micro cutting effect was reduced,but the wear resistance was improved.Ni60A-15%WC has the best wear resistance.The high temperature oxidation resistance of WC/Ni based composite cladding increases gradually with the increase of WC additive amount,which shows that the oxidation weight and oxidation speed decreases continuously,and the high temperature oxidation resistance of Ni60A-15%WC cladding is the best.For Co-based cladding,the high temperature oxidation resistance of the cladding increases first and then decreases with the increase of WC addition showing that the oxidation resistance of Co50-10%WC cladding is the best and Co50-15%WC cladding is the best Cladding level.Based on the analysis of the influence of WC additive amount on the forming quality,microstructure and properties of Co50 and Ni60A cladding layers,it is recommended that WC content should be 10%in Co50 cladding layer and 15%in Ni60A cladding layer.