Effect of binder phases on the cavitation erosion behavior of HVOF sprayed WC-based coatings

Abstract

In order to address the issue of cavitation erosion (CE) damage in marine mechanical components, WC-10Co4Cr (WCC), WC-10Co (WC1) and WC-17Co (WC2) coatings were prepared on the surface of 316L stainless steel using high-velocity oxygen-fuel (HVOF) spraying technique. The study investigated the microstructures, phases, mechanical properties and CE behavior of the coatings with different binder phases. The effects of the type and content of binder phase on the CE resistance and mechanism of the coatings were studied by compared the differences of volume loss rate (VLR) and eroded surface morphologies between the coatings. It was observed that all three coatings were dense and tightly bonded to the substrate. The primary phases identified in the coatings were WC, W2C and Co3W3C. Compared with the WC1 and WC2 coatings, the WCC coating demonstrated superior CE resistance with the lowest volume loss rate (VLR). The VLR of the WC1 and WC2 coatings was approximately four times higher than that of the WCC coating. The binder phase of Co-Cr improved the mechanical properties and the bonding strength of hard and binder phase, which reduces the brittle detachment of WC particles. In addition, the WCC coating had high microhardness and elastic modulus (E), H/E and H3/E2, which hindered the initiation and propagation of fatigue cracks. The initiation of CE damage occurred at the original defects, such as pores, cracks. The primary CE mechanism of the coatings was the interlinking of cavitation craters, lamellar spalling caused by the fatigue cracks propagation along the interlayer. The brittle detachment of WC hard particles also occurred significantly in WC1 and WC2 coatings due to loss of the binder phase. It was concluded that the binder phase markedly influenced the CE resistance and mechanism of the coatings, the addition of Cr showed the most pronounced effect.