Preparation of PTFE particles-doped manganese phosphating coatings on 20Cr steel and their wear and corrosion resistance

Abstract

Different PTFE particles-doped manganese phosphating coatings were prepared by changing the concentration of PTFE particles in a phosphating solution with 20Cr steel as the substrate commonly used for gears manufacturing. The experimental results show that the grain of different manganese phosphating coatings are polyhedral and irregularly distributed, with the size of 6–15 µm. PTFE particles in the manganese phosphating coating play a filling role in effectively blocking the penetration of corrosive medium and act as a solid lubricating medium to reduce friction in the friction process. Changing the concentration of PTFE particles in the phosphating solution has little effect on the grain growth, compactness and hardness of PTFE particles-doped manganese phosphating coating, but affects the wear resistance and corrosion resistance of PTFE particles-doped manganese phosphating coating. When the concentration of PTFE particles in the phosphating solution is 20 g/L, the PTFE particles in the manganese phosphating coating is 6.86 %. The phosphating coating prepared under the condition of 20 g/L PTFE particles in the phosphating solution has the lowest friction coefficient of 0.41, the lowest corrosion current density of 9.6 × 10−7 A/cm2, and the most positive corrosion potential of −552.4 mV, showing excellent wear resistance and corrosion resistance, which can play a good role in surface modification of 20Cr steel.