Coating of Sealing Surface of High-temperature Wear-resistant Ball Valves (Part one)

Coatings of Sealing Surface of High-temperature Wear-resistant Ball Valves (Part one)


The strengthening process of depositing CrN coating on Cr3C2-NiCr coating to form CrN or Cr3C2-NiCr composite coating by using supersonic flame spraying (HVOF) combined with physical vapor deposition (PVD), and the composite coating has been studied from microstructure design of thin films, friction, corrosion and mechanism of anti-friction and anti-corrosion.
 
1. Overview
At present, the wear-resistant coatings applied to the sealing surface of metal seated ball valves are mainly nickel-based alloy coatings, Cr3C2-NiCr coatings, WC-CoCr coatings and STL coatings. The pure nickel alloy coating has limited performance and does not greatly improve the service life of the ball valve. Although Cr3C2-NiCr, WC-CoCr, and STL coatings have good wear and corrosion resistance at room temperatures, their hardness decreases seriously with the increase in temperatures, and the porosity of the coating is big, which has an adverse effect on the anti-corrosion of the coating. Therefore, the necessary surface treatment should be adopted to strengthen the sealing surface of the ball valve, improve the hardness, wear resistance and anti-corrosion of the sealing surface of the ball valve, and effectively prolong the service life of the ball valve. Researching high-temperature wear-resistant ball valves has very important social and economic significance.
 
2. Strengthening processes
High-temperature wear-resistant ball valves are mainly used in the coal chemical industry, coal oil, polysilicon, catalyst and other working conditions containing solid particles. At present, a variety of wear-resistant materials have been applied to the sealing surface of valves to meet the requirements of various harsh working conditions. In recent years, the technology of using physical vapor deposition (PVD) to treat the metal seated surface of ball valves has developed rapidly. PVD technology refers to the use of physical methods to vaporize the surface of materials (solid or liquid) into gaseous atoms, molecules or ions under vacuum conditions, and through the process of low-pressure gas (or plasma) to deposit some special properties on the surface of the substrate. PVD technology can deposit carbides of various metals (Ti, Zr, Cr, W, etc.) and nitrides of metals such as Ti, Zr and Cr and nitrides and carbides of other binary or multiple alloys on the surface of the ball valve. These films generally have good hardness, good wear resistance, corrosion resistance and high-temperature resistance. When deposited on the sealing surface of the ball valve, a superhard corrosion-resistant coating can be obtained. The microhardness is greater than 1800 HV, which can greatly improve the corrosion resistance of the service life of the component.
 
3. The research content
The CrN coating is deposited on the Cr3C2-NiCr coating by the supersonic flame spraying (HVOF) process combined with PVD technology so that it can be combined with the Cr3C2-NiCr intermediate layer to form a CrN or Cr3C2-NiCr composite coating. Starting from the microstructure design of the thin film, friction, corrosion and anti-friction and anti-corrosion mechanism, the controllable preparation of high-performance wear-resistant and anti-corrosion integrated DLC coating and its friction and corrosion behavior were studied by using unbalanced magnetron sputtering technology. The description of the coating’s research content is shown in Figure 1.