High-temperature sliding wear performance of HVAF sprayed WC-based coatings with alternative binders

The wear performance of HVAF sprayed WC-based composite coatings with Co-lean or Co-free binders was evaluated as an alternative to conventional WC-CoCr wear-resistant layers. The coatings were characterized for microstructure and tested for their micro and nano hardness. Their tribological behavior was studied for reciprocating sliding wear at room and elevated temperature (-300 degrees C). Using nanoindentation, the hardness of carbide grains was measured to be between 18 GPa and 25 GPa. Nanoindents that fell in the binder phases had a hardness of 15 GPa-18 GPa, which, due to the fine scale of the microstructure, represents some average mixture of the binder and carbide. Using Vickers indentation at higher loads, the hardness values of the coatings at room temperature were found to be between 1000 and 1200 HV0.3, which decreased by -200 HV0.3 when tested at elevated temperatures. The wear performance of all coatings with alternative binders at room temperature was comparable to that of the reference WC-CoCr. However, the specific wear rates of the coatings tested at elevated temperature was higher by 1-2 orders of magnitude compared to those performed at room temperature. With the exception of WC-FeNiCrMoCu, the other three coatings exhibited comparable high-temperature wear performance. Ripple-like patterns were the prominent feature observed on the room temperature wear tracks. At elevated temperatures, wear tracks showed macro cracking and micro fatigue cracks, as well as pitting and oxide formation on the surface of wear track.