Study On WC/Ni Composite Braze Coating Process And Self-Sharpening Of Tools With Unilateral Coating

Common agricultural tools are easy to be worn seriously and cutting resistance can be increased because of passivated blades,which will decrease their sharpness and plowing efficiency.Although good wear-resistant material or the use of strengthening process can promote the wear resistance of tools,the difficulty of self-sharpening of tools is still unable to be resolved.Therefore,the mixture containing WC and Ni-based alloy powder was used in this study to fabricate unilateral coatings on 45 steel tools.The aim was to make tools with two surfaces different in hardness.The theoretical and experimental basis of improving self-sharping of tools and fabricating tools with long service life can be provided.The following innovative works were completed in this study:(1)The DTA thermal analysis of the mixture containing 30 % WC and 70 % Nibased alloy powder indicates that the initial melting temperature of the Ni-based powder is 901.5 ? and the finishing melting temperature is 1029 ?.They are respectively 33 ? and 15 ? lower than those of the Ni-based alloy powder,which is in favor of the reduction of the decomposition of WC.(2)The comparison of different brazing coating processes indicates that the process of 1150 ? for 30 seconds can ensure the completeness of the melting of Ni-based alloy powder.The thermal damage of WC particles can be also decreased in this way.The microstructural observation indicates that WC is the hard phase of the coating and also have the effect of inoculation,nucleation and grain refinement.This process can improve the holding strength of Ni-based alloy towards WC.(3)The plowing simulation test of tools with different coating thickness indicates that coatings with different thickness provide different protection to tools,which also affects the curvature changes of blades.The suitable thickness can only make tools have excellent self-sharpening.Under one test conditions in this study,tools with 60 ?m thick coating are sharper and have better self-sharpening,followed by tools with 80 ?m,100 ?m and 40 ?m thick coating and free coating.(4)The plowing simulation test of tools after different heating treatment indicates that unilateral coating tools quenched can keep the blade in a state of smaller radius of curvature in a long time and their service life is long.The tool quenched and 600 ? tempered have the max difference between substrate and coating in hardness.The selfsharpening is obvious and the cutting resistance is low.Therefore,the abrasion can be decreased and the service life can be promoted.The self-sharpening and service life of tools normalized are the same as tools quenched and 400 ? tempered.