Preparation Process And Microstructure Properties Of Ni-based Composite Brazing Coatings For Agricultural Machinery Components

The early failure and scrapping of the soil-engaging components of agricultural machinery such as plowwalls,ploughshares,and harrow blades during operation due to wear,corrosion,and adhesion seriously shorten the service life of agricultural machinery.With the development of modern agricultural machinery in the direction of large-scale and compound,higher requirements have been put forward for the comprehensive properties of the soil-engaging components.The optimization design and surface modification of the soil-engaging components have become a hotspot for scholars at home and abroad.Therefore,it is of great engineering significance to systematically carry out the research of high-performance surface reinforcement layer grinding grain wear in China from an agricultural country to an agricultural power.In this paper,BNi-2 powder brazing filler metal is selected,and the WC particle-enhanced composite brazing coating is prepared on the surface of austenitic stainless steel by vacuum brazing coating process by adjusting the WC content and particle size of hard particles.The microstructure and composition identification were observed by scanning electron microscope additional energy spectrometer and X-ray diffractometer,and the coating properties were tested by means of microhardness tester,friction and wear tester and Rockwell hardness tester,and the wear mechanism of the coating was analyzed.First-principles analysis of the coating-bonding interface.The main work of this paper is as follows:MS CASTEP software was used to study the interface behavior of nickel-based solder and WC hard phase.For the two end-capping methods of C and W of WC,the convergence test was used to ensure the accuracy of the calculation,the separation work was used to determine the bond strength,and the electronic structure was used to analyze the nature of the interface formation.It provides a theoretical basis for studying the microstructure and properties of brazed coatings.With the increase of WC content,the internal compactness of the coating decreases and the porosity increases;the segregation of WC particles in the nickel-based solder is alleviated,the distribution is gradually uniform,and the wear resistance is also improved;The critical load P_cof the composite coating decreases gradually with the increase of WC content.As the WC particle size decreases,the internal compactness of the coating increases,the critical load P_cof the coating increases gradually with the decrease of the WC particle size,but the fluidity of the solder decreases,and the wettability to the base metal becomes poor;the dissolution of WC particles in the nickel-based solder intensifies.The optimal preparation formula of nickel-based composite brazing coating is 25wt.%WC,WC particle size is 100 mesh,brazing temperature is 1030℃,holding time is 30min,heating rate is 15℃/min,and vacuum degree is5×10^-3Pa.The composite coating structure prepared by the optimal process has the characteristics of bezel,a small amount of Cr₂B phase,Ni-W phase and nickel solid solution are formed at the interface,and the WC particles,nickel-based brazing filler metal and steel matrix form a metallurgical bonding interface.The porosity of the coating is 1.35%.The WC particles are evenly distributed in the nickel-based brazing filler metal,and the nickel-based brazing filler metal has the effect of consolidating and supporting the particles.The WC particles act as a hard phase to prevent the effect of abrasive particles on the ploughing of the brazing coating,thereby reducing and weakening the damage of the abrasive to the brazing coating.The wear resistance of the composite coating is 15.7 times that of the steel matrix and 5.9 times that of the high manganese steel.The diffusion of elements between the coating and the steel matrix is mainly manifested in the dissolution and diffusion of Fe,Cr and Mn elements in the steel matrix into the coating structure,and segregation and precipitation at the grain boundary of the coating structure,and a network structure is formed on the steel matrix near the interface,greatly improving the bonding strength of the composite coating and the steel substrate.From the crack growth morphology of Rockwell indentation,there is no obvious deformation on the surface of the coating,the crack opening is flat,and many fragments are formed at the fracture,which belongs to brittle fracture.The location of crack propagation is in the hard phase WC particles and the W-rich phase.