Preparation And Study On Wear And Corrosion Resistance Of Ni And WC Based Thermal Spray Coatings

Due to its high hardness,excellent wear resistance and good corrosion resistance,thermal spraying coating is widely used in extreme wear and corrosion conditions such as valves,fan blades and construction machinery picks.With the development of oil and gas production to ultra-deep formation,the BOP plug valve ball,as an important drilling safety tool in the drilling process,is in service in the downhole high temperature,corrosion and wear environment,facing serious safety risks.Therefore,developing new material protection technology to improve the wear resistance and corrosion resistance of the cock valve ball of the blowout preventer has become a research hotspot.In this paper,16Cr Mn Mo high-strength martensitic stainless steel in present service is used as the matrix,and the Ni base coating and WC base coating are prepared on the surface of the material by spray welding and supersonic thermal spraying technology.The influence of the coating system and processing method on the performance of the wear-resistant anticorrosive coating is studied.On this basis,the coating is closed with high temperature resistance to effectively improve the corrosion damage life of the coating.The results show that the coating preparation method has significant influence on the coating properties.The spray welding process can realize the metallurgical bonding between the coating and the stainless steel matrix,but there are many penetrating microscopic cracks in the coating due to the intense cooling process.With the increase of coating thickness,the corrosion resistance is improved significantly.When the coating thickness reaches 200μm,the corrosion resistance of the coating decreases.The number of cracks caused by residual thermal stress leads to the increase of corrosion resistance.There are micro pores in the supersonic spraying coating.The micro-hardness and friction and wear properties of the coating are reduced by the spraying process compared with the spray welding.However,it has little influence on the properties of the matrix stainless steel material.Two kinds of WC coatings of WC-20Cr₃C₂-7Ni and WC-10Co4Cr,were prepared by supersonic thermal spraying technology.The results show that the porosity of WC coating is significantly lower than that of Ni60 coating,and the hardness,wear resistance and corrosion resistance of WC coating are better than that of Ni60 coating.The mechanical properties and corrosion resistance of WC coating are the best when the coating thickness is 150μm,and the comprehensive properties can be effectively improved by adding a certain amount of Co to WC coating.The service life of superhard coatings in high temperature water medium was further improved by using phosphate to seal micropores of coatings by sol-gel method.The results show that Al PO₄ and Al₂O₃ can achieve uniform coverage of micropores,and the comprehensive performance of the coating is significantly improved after sealing treatment.Long-term impedance tests of the three 150μm-thick coatings after sealing showed that all coatings maintained good corrosion resistance after 30 days of immersion,indicating that the sealing treatment significantly improved the long-term corrosion resistance of thermal-sprayed coatings.Among them,the WC-10Co4Cr coating exhibited the best corrosion resistance after sealing.