| The development of modern industry can not be separated from metal, especially the basic application of steel and iron materials. Even in today's science and technology, steel and iron still account for 60 percent to 70 percent in the usage of metallic materials. While the high-temperature oxidation of damaged materials is one of the main failure modes, in particular in the industrial, water conservancy and metallurgical application. In order to improving oxidation resistance performance and thermal stability of steel and iron, special steel or special cast iron which contents high alloy composition is used usually. However overall alloy materials can enhance the oxidation resistance performance and thermal stability, but most mechanical part's oxidation and damage take place in their contacts with special surface and certain part which works in specific environment. So overall alloy is not economy. The hardening technology which compose various heat-resistant and oxidation resistant materials in surface in solving these problems shows enormous superiority. Model cluster is bonded by foam model which is similar to casting size and shape.Brush refractory paint on the model and dry, bury it in the quartz and vibrate for modeling. Pouring in under negative pressure so that the liquid metal occupy the model location after it is gasified, then cooling and solidification to form the casting. EPC casting is a new casting method which use above craft to obtain the casting.Casting infiltration is material surface technology, which fix alloy powder particle on specific location of die space and then through one-time casting form the composite surface with wear-resistant, heat-resistant and corrosion-resistant property. That technology combine traditional casting with composite technology of material surface and through one-time casting make full use of residual heat produced in the process of casting and solidification.Casting infiltration technology not only reduce energy consumption, simplify procedures, improve significantly the practical life of the casting, but also has many other advantages such as not require special equipment, operates simply, short production cycle, saving materials, technology easy, convenient shape, thick surface composite, not distortion and can be heat treatment of the parts and so forth.In this paper, the heat-resistant and anti-oxidation alloy layer of cast iron surface has been prepared through the method of EPC gravity infiltration, which achieve surface alloy of cast iron. What's more, microstructure and performance of the alloy layer should be researched. First, select base materials, alloy particles, binder, flux and then confirm their proportion. Second, coating material mixed evenly will be brushed on the surface of EPC model, next dry it, afterward brush refractory material and dry. Finally, prepare for sample, observe and analyze the microstructure of alloy layer, do heat-resistant and oxidation resistance experiment.Microstructure, elemental composition and phase composite will be researched through optical microscopy, X-ray diffraction, scanning electron microscope and other modern analytical techniques. Following conclusion can be inferred from the analysis of above experiment:(1) Certain thickness alloy layer can be obtained by coating particles. The thickness of alloy layer is between 1mm-2mm.(2)The junction between coating and substrate becomes fuzzy even fusion. Simultaneously, growth trend emerge from coating to substrate. Qualification of coating is improved such as fewer pore, smaller pore, fewer impurity and so on.(3)Scanning the interface between coating and substrate shows chemical element distribution of junction. Fe, Ni, Mo, Cr element content change can be seen from the scanning result, which explain phenomenon of proliferation between alloy element and iron cast substrate.(4)X-ray diffraction results of junction between coating and substrate show that: many inter-metallic compound and alloy carbides occur in the interface. From the result, we can infer reaction-diffusion and metallurgy union between coating and substrate.(5)Coating alloy particles influencing by quantity of iron melt heat can be melted and condensed to form infiltration outer alloy layer. The heating response time of alloy particles outer layer is short and the extent is weak. Low-melting-point binder and solvent is melted firstly. Then, edge of small particles and alloy surface can be melted. Big alloy particles may disintegrate into small particle finally. Melting alloy liquid plays the role of binder in the process of cooling. That alloy fluid infiltrates between alloy particles and then coagulate. In that process the particles are not melted, which will sintered to form infiltration outer layer.Thermal-fatigue and oxidation resistance of casting can directly affect their application in high-temperature working environment. Oxidation weigh gaining experiment and thermal-fatigue experiment should be implemented in cast iron sample and the sample with alloy layer. Analyze experimental result and obtain the following conclusions:(1)Thermal-fatigue crack quantity of alloy layer formed by alloy particles is fewer than cast iron. The length of crack is much shorter. Under 800℃, cast iron thermal-fatigue crack initiates at 800 times and alloy layer at 1200 times. Crack growth speed of alloy layer is faster than cast iron.(2)After oxidation 4h at 800℃, oxidation gaining weigh speed of alloy layer is slower than cast iron but not obviously. After oxidation 5h at 950℃, oxidation gaining weigh speed of alloy layer is less than cast iron distinctly. Oxidation rate of cast iron is three times than sample R1. Alloy particles have evident improvement to oxidation resistant of cast iron surface.(3)Alloy layer adhesion strength is consistent with coating thermal-fatigue properties. The coating with well thermal-fatigue property has good adhesion strength correspondingly. The emergency of inter-metallic compounds has proofed metallurgy union in the junction between coating and substrate and enhancement of adhesion strength. So thermal-fatigue property has been improved prominently.Casting iron surface infiltration technology form alloy layer on the surface of casting, which produce metallurgy reaction between metal liquid and alloy power directly. The metallurgy reaction process makes use of liquid metal infiltration ability and quantity of heat. Casting infiltration process not only contains molten metal to compound granular materials soakage and infiltration, but also has interface reaction in certain extent. The formation of infiltration is a common result operated by thermodynamics and kinetics. Infiltration process includes following three stages: molten iron into the alloy particles, molten iron contain alloy particles and coating alloy particles molten and condensate for forming infiltration outer layer under molten iron hot function. Metal power particle size, surface tension of molten mental, wettability between metal liquid and particle, static stress of liquid metal, vacuum degree of model, the duration of metal liquid and metal liquid viscosity are main factors which have a great effect on infiltration depth and rate. |
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