Experimental Study Of Anti-erosion Of HVOF CoNiCrWC Coating By Laser Melting

Turbine blade is the part that transforms gas linear motion of the high temperature and pressure into axis rotation. Turbine usually work rate of 3000 r/min, the speed is almost supersonic in the edge of the last stage blades. The rotor blades that work in the wet steam region impacted by water droplets, it produce pressure between water droplets and the rotor blade, the pressure exceeds the material yield limit, the material of the blades produce a localized plastic deformation. This pressure acting on the blade again, material up to the fatigue limit, the local began to fatigue crack. Serious water erosion increases the risk of blade fracture, blade fracture will lead to strong vibration vicious incidents occurred, resulting in huge economic losses.therefore, extend the service life of blades, It is great significance to ensure the safe operation of the power plant.With the rapid development of laser technology, laser melting has been relatively better. It is more obvious advantages that laser melting compared with other, the laser alignment accuracy as a heat source, beam can be precisely controlled size, there is metallurgical combination interface between melting layer and substrate , the thermal deformation and thermal effect of substrate are relatively small.In this paper,For principle of water-erosion,design CoNiCrWc composite coating, CoNiCrWC coating technology have been obtained by laser melting, the microstructure of the laser melting were observed by SEM and OM, tested microhardness and wear resistance of the melting layer, analyzed the factors that affect the crack behavior. and study of erosion resistance. The results show that:1. The microstructure of CoNiCrWc coating of the last stage blades were observed by SEM and OM, there is better metallurgical bonding between melting layer and substrate. There is uniform microstructure in melted layer.2. substrate preheating temperature and thickness that have some influence on the blade coating cracking behavior, it can inhibit the crack occurred through the preheating temperature;crack width of the melting layer increases with the coating thickness, that need the higher the preheating temperature to eliminate cracks.3. The average microhardness of the melting layer is HV0.2964.314, micro-hardness is 2.288 times the substrate. In the same experimental parameters, the wear volume decreased by about 89%, the wear resistance of the melting layer more marked increased than in the substrate, observed the roughness of the wear specimen show that the coating has a smoother surface.4. It designed CoNiCrWc coating, according to last stage blade the mechanism of erosion damage, composite coating can effectively reduce the bending stress that generated internally ,to provide a shear strain region, that WC layer is not susceptible to brittle fracture, reducing the erosion rate. Through anti-erosion test results, the last stage blades erosion resistance increase with the increase of microhardness, the anti-erosion performance of melting layer is better than the substrate.