Preparation Of SiC Particles Reinforced Steel Matrix Surface Composite And Investigation On Its Erosion Wear Properties

Approximately 75%-80% failures of parts are caused by wear in the application, wear is the main reason to result in the failure of components. With the development of huge production equipment, there are more stringent requirements for the wear resistance to the materials. However, it is very limited for the traditional materials to improve the properties, and it is difficult to meet this stringent requirements. Recently, more attentions have been paid to the particles reinforced metal matrix composites since they combine good thermal stability and good ductility of metals with good erosion resistance, high temperature oxidation resistance and wear resistance of ceramic particles. In the present investigation, the research background is that these easily worn components, such as slurry pump and dreg pump, are usually used in working conditions with low stress and erosion wear. The SiC particle reinforced steel matrix surface composite was prepared by expandable pattern casting and casting infiltration process, the effect of the constituents of prefabricated SiC loaf and the parameters of expandable pattern casting and infiltration on the compound quality of SiC/steel is studied. The optimum vacuum evaporative pattern casting (V-EPC) infiltration preparation technology of the SiC particle reinforced steel matrix surface composite was determined through the analysis of the macro/micro-structure, bonding interface structure and composition. The slurry erosion wear performances of the SiC particles reinforced steel matrix surface composite, Q235 steel, high chromium as-cast iron and low chromium as-cast iron were studied on the self-made slurry inject erosion wear machine, and their erosion and wear mechanisms were analyzed.The SiC particles reinforced steel matrix surface composite was prepared successfully by the vacuum evaporative pattern casting (V-EPC) infiltration technology on the substrate of 35 steel with the SiC particle 600μm to 850μm in diameter, 2wt% high purity clay as adhesive, and additives of 2wt%NdF and 2wt% boric acid, and through controlling casting temperature and proper vacuum evaporative pattern casting (V-EPC) infiltration. The good surface casting-infiltration layers are formed between SiC ceramic particles and substrate, there are obvious composite layers, transitional zone and substrate zone. The expression of casting-infiltration velocity and casting-infiltration layer thickness was deduced from the analysis of thermodynamic and kinetics of casting-infiltration process. The main factors affecting vacuum casting-infiltration velocity and depth are the size of SiC particles, surface tension of molten steel, wettiability between molten steel and SiC particle, the static pressure of molten steel, the mold vacuum, the holding time of molten steel and the viscosity of steel et al. The thermodynamic evidence that SiC must be decomposed during the pouring process of molten steel was obtained from theory. It is proposed that the reaction kinetics process can be controlled by changing experimental conditions and technological parameters, thus retard the decomposition rate of SiC. The effect of various adhesives, flux and the addition contents on the quality of vacuum casting infiltration surface composite was investigated, and the optimum preparation parameters of the SiC particle reinforced steel matrix surface composite was determined.The necessary condition of preparing SiC particles reinforced steel matrix surface composite by vacuum evaporative pattern casting (V-EPC) infiltration was put forward, that is, X value, the ratio of casting thickness and the perform thickness. When X is between 4 and 8, the good SiC particle reinforced steel matrix surface composite can be obtained.The microstructure, composition of casting-infiltration surface compound layer and the bonding interface between SiC particles and matrix were analyzed. The main microstructure of casting-infiltration compound layer is consisted of SiC particles, steel matrix and graphite, the SiC particles are distributed uniformly and arranged tightly without agglomeration, the SiC casting-infiltration compound layer has a metallurgical bonding with steel matrix, thus has a larger bonding strength. The matrix of steel is mainly ferrite, but pearlite also appears under certain conditions. The microhardness of matrix around SiC particles decreases with increasing the distance from the centre of SiC particles, the addition of SiC particles enhances the whole hardness of the composite. Due to the existence of transition zone, there is a gradually decreased hardness gradient from the compound layer to the matrix, the hardness of compound layer is distributed in gradient as well. The gradually negative hardness gradient is beneficial to enhance the slurry erosion wear resistance.The reasonable adjustment of additive constituents of prefabricate SiC loaf can not only guarantee the steel infiltration, but also prevent the decomposition of SiC particles. The reaction products in the interface between SiC particles and steel matrix are oxides and complex compound oxides. The formation of interface reaction layer improves the bonding strength between SiC particles and steel matrix, and decreases the thermal stress caused by the difference of elastic modulus and thermal expansion coefficient.An inexpensive and conveniently operated slurry erosion wear test apparatus was researched and developed ultilizing the knowledge of machine design and manufacturing, hydromechanics principle and the hydraulic engineering principle etc. The test results show that slurry erosion data of the apparatus is repeatable, and the test machine is a reliable apparatus which is suitable for abrasive material selection and erosion wear mechanism research. The slurry erosion wear tests show that the wear mechanism of the SiC particles reinforced steel matrix surface composite is cutting and ploughing when the jet angle is low. The SiC particles reinforced steel matrix surface composite has the best relative erosion wear property of at 45°jet angle, which is 3.03 times than that of the Q235 steel. The erosion wear rate of composite decreases with increasing the jet angle in the range of 60°～90°due to the supporting effect of the matrix on the reinforced particles and the protecting effect of the SiC particles on the matrix. The wear mechanisms of the SiC particles reinforced steel matrix surface composite are impact fracture and cutting. The SiC steel matrix surface composite reinforced with 850um SiC particles has better slurry erosive wear property than that reinforced with 600um SiC particles. The erosion wear rate of SiC steel matrix composite increases with increasing size of quartz particles in the slurry.With increase of jet angle, the erosion wear property of the high chromium cast iron first increases and then decreases, the peak value appears at 60°. Its wear mechanisms are brittle fracture and flaking. The low chromium cast iron has excellent slurry erosion wear resistance when the jet angle is less than 45°. Its erosive wear mechanisms are cutting and ploughing. The slurry erosion wear resistance of Q235 steel has plain property and its erosive wear mechanisms are cutting and impact wear.