The elevated-temperature wear behavior evolution of HVOF sprayed tungsten carbide coatings: Respond to heat treatment

In this work, WC-Co coatings were sprayed by high-velocity oxy-fuel (HVOF) thermal spray. The high-temperature sliding tests of WC-Co coating were conducted, and the effects of heat treatment on the high-temperature wear properties were investigated. The results show that the microhardness of the as-deposited WC-Co coating was 803.7 +/- 24 HV0.3. As the sliding temperature increased from 25 to 550 degrees C, the average friction coefficient and wear rate of as-deposited WC-Co coatings increased firstly and then decreased. The minimum wear rate of 3.65 x 10(-6) mm(3).N-1 m(-1) was obtained at 450 degrees C. The reduced friction coefficient was due to the formation of lubricating WO3 and CoWO4 phases. The improvement of coatings wear resistance was due to the enhanced hardness. After heat treatment at 450 degrees C for different time, the predominant phase was kept as WC, and few oxides formed. The maximum microhardness was 1378.3 +/- 41 HV0.3. For heat treated coatings, with the increase of the sliding temperature, the reduced friction coefficient was also due to the formation of lubricating phases (WO3 + CoWO4). The low load-bearing capacity and more oxides due to the oxidation at elevated temperatures can account for the increase of wear loss. The dominated wear mechanism was oxidative and abrasive wear.