A Novel Oxide Layer Formed on the 800 °C-Annealed CoMoCrSi Coating Significantly Reduced Friction and Wear at Room Temperature

In the present work, we investigated the microstructures and properties of as-sprayed and annealed CoMoCrSi coatings. Specifically, the annealed treatment at 800 °C resulted in good recrystallization, improved microstructure, and enhanced properties of CoMoCrSi coatings. An oxide layer formed on the annealed coating surfaces; it was mainly composed of nano-sized Cr2O3 and micro-sized CoMoO4, and could account for the increased surface microhardness and enhanced anti-wear performance of annealed coatings. In particular, the very hard Cr2O3 played a critical role of resisting press-in and wear during the tests, and the CoMoO4 had a lubricating effect during the friction process. Finally, the annealed coatings exhibited low coefficients of friction (COFs) of 0.4 and wear rates of 0.7–0.8 × 10−6 mm3·N−1·m−1 after a long sliding distance of 1000 m at RT. Consequently, the wear mechanism transferred from brittle fracture coupled with abrasive wear for the as-sprayed coating to slight abrasive wear for annealed coatings.