Preparation And Characterization Of Wear Resistance And Corrosion Resistance Cladding Layers

Lots of wear and corrosion occurred in the electric power industry, especially in coal-fired power stations and biomass power plant. The wear of boiler auxiliary equipments is one of the main reasons to reduce the unit output. Wear cause the devices to be forced to drop the load operation, frequent maintenance or replacement of the parts, and even downtime. Wear has become an important factor to affect the safety and economic operation of thermal power plant. The most severe wear usually occurred in mill, mill exhauster and induced draft fan. Wear maintenance costs of mills accounted for a large proportion of maintenance costs of the thermal power plant. While wear problems of induced draft fan and exhaust powder have seriously affected the safe operation of thermal power plants.High chlorine content in the biomass raw material and large amounts of alkali metal chlorides in the ash after combustion of the biomass will obviously cause serious chlorine corrosion on the water wall tubes and superheaters at a certain temperature, resulting in serious effect on safe and economic operation of the boiler. Superheater is a common fault of the biomass power plant. When beyond the temperature of superheaters, burst pipes serious accident may occurs due to severe high temperature chlorine corrosion even the excellent corrosion resistance of the TP347stainless steel was used.The new preparation technologies, properties and practical application of wear and corrosion resistance cladding layer are the focus of this article. The researches are of great clinical significance in improving the security level of economic operation of important components in power plants.In this paper, the composition, preparation method and characteristics of high wear-resistant TiC-Ni based ceramic-metal composites and cladding layers are studied, these will provide an important basis for application in the induced draft fan, exclusive powder impeller and roller.TiC-Ni based ceramic-metal composites prepared by hot pressing reaction synthesis techniques. The resulting product was composed of two phases:TiC and Ni. And the ceramic particles are mainly characterized by the five kinds of rim/core morphology.TiC-Ni based ceramic-metal cladding layers prepared by TIG welding. Microstructure, hardness and wear resistance were analyzed. The cladding layer was composed of TiC and Ni. The rim phase was not found in the cladding layer, complete solid solutions were formed between WC and TiC. Cladding layer shows a higher hardness and better wear resistance. Based on the multivariate composite of ceramic materials to improve the basic mechanical properties and wear resistance of ceramic-metal composites, WC, NbC, Mo and Co were added to the TiC-Ni composites. It can be seen that the cladding layers were dense and ceramic particles dispersed in the binder matrix.More voids and cracks occurred in the ceramic particles by adding15wt%of WC or NbC to TiC-Ni based ceramic-metal cladding layers separately. Under the10wt%NbC condition, there are more cracks, hole and other defects in ceramic particles when adding15wt.%WC; while there are little cracks, hole and other defects in ceramic particles when adding20-35wt%WC. This shows that the internal defects of the ceramic particles can be effectively reduced by adding of NbC and WC.The maximum hardness and the maximum compressive strength of the cladding layer occurred in the cladding layer of20wt%WC.In this paper, Ni-Cr-Mo corrosion resistant cladding layers formed on the surface of TP347superheater tube were prepared by a laser cladding and TIG welding. The metallurgical bonding exists between the cladding layers and the substrate. The changes of elements content of cladding layers before and after cladding were compared.The EDX result revealed that content of Cr in cladding layer almost remains unchanged, before and after cladding, while the average content of Fe in the cladding layer has increased six times than the original wire. The mass percentage of Ni and Mo in the cladding layer are greatly decreased, thereby the corrosion resistance of the material is reduced. Dilution rate of Fe in the cladding layer by laser cladding is far less than the obtained value of TIG welding.High temperature chlorine corrosion experiments were conduct on samples of laser cladding layer, TIG cladding layer, C22, and TP347H. Results show that the curves of corrosion kinetics at different temperature are similar to the parabolic, and the rate of the weight gain increases with time. The minimum corrosion rate was obtained in the laser cladding layer. After the corrosion test, the samples of C22, TP347H and TIG cladding layer were inhomogeneity, the holes formed in part of the region, while laser cladding layer are still dense. XRD analysis of corrosion products on the sample at700℃show that iron and chromium oxides formed in the four samples, but chloride was not found. Fe-Ni-Cr-Mo is still the main phase of the laser cladding layer. Laser cladding layer showed the best resistance to chlorine corrosion.The ceramic-metal composites and preparation technologies discussed in this paper were applied in the wear parts, such as exclusive powder machine and grinding roller, et al. Results show that the impeller is largely intact after running for18,520hours, the original welds are visible and no shedding and severe wear are found. The life of impeller made by the technique of this paper is up to10times the new impeller, and life extension up to six times compared with conventional abrasion treatment. For grinding rollers with ceramic-metal cladding layers, wear serious parts is the outer edge of the Grinding roll face, and the wear depth is about2-5mm after running for4920hours. The wear of cladding surface appears uniform, and peeling off of the cladding layer is not found. The actual wear resistance of the ceramics-metal cladding layer is about4-6times the ordinary wear-resistant surfacing materials.