Investigation Of The Microstructures And Properties Of Laser Cladding Co-based Ceramic-metal Composite Coatings

Slide valves of catalysis fitting were worked in high temperature (about 700℃) flue gas with catalyst particles. Guides and valve plate of which were usually failure in the severe enviroment. The internals were often strengthened or repaired by hot spraying or surfacing technology, which had a lot of advantags and some insurmountable disadvantages.5kW laser with CO2 flow transverse was used for cladding Stellite6/WC powder on 1Cr18Ni9Ti stainless steel surface. The appropriate selection of the process parameters can obtain defect-free fine micro-structures. By means of SEM, TEM and EDAX, the effect of cladding technology on the microstructures of the laser cladding coatings were studied.The result indicated that the microstructures of the laser cladding layers were fine and defect-free and good metallurgical bonding between the coating and the substrate was obtained. The results showed that microstructures of the coating consisted of plane, cellular and dendrite, and the coating has higher hardness which was about 2-3 times of the matrix. When adding appropriate amount of Al with low melting point into the Stellite6/WC powder, the porosities disappeared in argon protecting. The microstructure at the cladding layer bottom was the typical extension growth on plane basis, the morphology of grains changed from planar and cell to dendritic which was coarser. The microstructure at the top and middle was the regular pine-tree crystal and the microstructure at the top was the small pine-tree crystal, respectively. In the guarantee of the forming of the metallurgical combination between coating and substrate, increasing scanning speed or decreasing power density properly would profit the refinement of the coating structure. So the laser cladding process of Co-based composite metal ceramic can improve the performance of stainless steel. High-temperature oxidation tests were researched at 700℃. Oxidation test results at high temperature showed that the high-temperature oxidation resistances of the Stellite6 and the Stellite6 with 10%WC(2%Al) layers were better than the matrix.The erosion-corrosion wastage of coatings and the matrix at 700℃was researched with 90°impact angle. As compared with the matrix, the erosion-corrosion resistances at elevated temperature of Stellite6 and Stellite6 with 10%WC(2%Al) coatings were higher. Especially, the Stellite6 with 10%WC(2%Al) coating presents the best erosion-corrosion resistance.