Study On The Microstructure And Capability Of The HVOF Spraying And Designing Of The Laval Nozzle

In order to prolong working time of the oil equipment, we sprayed two kinds of cermet coating including Ni-Cr-C and WC-Co by HVOF skill. Contrast the two kinds of coating's capability and microstructure. Discuss the law of influence to the particles' velocity, temperature and pressure by the parameter of the HVOF gun. And study the reason that leading to a lot of nubble in the Laval nozzle between the spraying discourse.The technical parameter of dimethylmethane influences the capability and microstructure obviously. Both the middle and high parameter of dimethylmethane can produce excellent coating. When the parameter of dimethylmethane is low, the integration capability is of poor quality. Ni-Cr-C and WC-Co coating have good capability that can be able to bear abrasion and combining. Beside that, the coatings have good capability to bear erosion in HC1 condition, too. Carbide in the Ni-Cr-C coating decomposes little. Quite a lot of carbide is dispersion in the Ni-Cr-C coating. Because of that, the capability to bear erosion is better than WC-Co coating. The microstructure of WC-Co coating is compact. So the capability to bear erosion in HC1 condition is better than Ni-Cr-C coating. The invalidation theory of abrasion is that the minicrack extends along the layer in the coating. When the abrasion angle is small than 60°, invalidation character of the coating is fatigue and minicutting. When the abrasion angle is big than 60°, invalidation character of the coating is fatigue . The temperature field, speed field and pressure field in the gun infer to the angle of the Laval nozzle. When prick angle increases, the temperature and pressure of the Laval nozzle decrease. When prick angle is 40°, the particle's velocity is low because that the accelerating function is limited. When prick angle is 60°, the particle's velocity is the biggest. When prick angle is 80°, because of the high contrary pressure, the part of heat energy transforms to kinetic energy is small. So the particle's velocity is low the that of 60°. The influence factors to the nubble in the Laval nozzle include material, spraying technical parameter, roughness inside the Laval nozzle, temperature of the circular water, granularity of the powder and length of the gun. All of that, the most important factor is roughness inside the Laval nozzle. Select velvet Laval nozzle, middle parameter of dimethylmethane, middle length of the Laval nozzle and control the temperature of the circular water can partly solve the problem.