Tribocorrosion behavior of HVOF sprayed WC-based cermet coatings in sodium chloride solution environment in relation to binder phases

Abstract

The performance of three WC-based coatings prepared by high velocity oxygen-fuel (HVOF) has been evaluated under both pure mechanical wear and tribocorrosion in 3.5 wt% sodium chloride solution environment. The synergism of corrosion and wear is also calculated. The three coatings were WC cermets with Co, CoCr and Cr3C2-7Ni matrices. The experimental results indicated that the binder phases in the as-sprayed coatings greatly influenced their corrosion and wear performances. In the pure mechanical wear, the WC-12Co coating showed the best wear resistance followed by the WC-10Co4Cr and WC-Cr3C2-7Ni coatings. In tribocorrosion, all three coatings were under corrosion-dominated regime. The WC-12Co coating had the highest corrosion rate result from the selective preferential dissolution of Co phase. The wear process further accelerated the dissolution and removal of Co for the highest material loss rate of WC-12Co coating. The WC-10Co4Cr and WC-Cr3C2-7Ni coatings showed great corrosion resistance due to the CoCr and (W,Cr)2C phase, respectively. However, the (W,Cr)2C brittle phase was easily broken down mechanically which increased the material loss of WC-Cr3C2-7Ni coating. The formation of CoCr phase reduced the dissolution of the Co and was not easily destroyed under loading, making the WC-10Co4Cr coating have the best tribocorrosion resistance.