Mo and W as alloying elements in Co-based alloys—their effects on erosion–corrosion resistance

In this paper results from erosion–corrosion tests performed under liquid–solid erosion conditions in 3.5% NaCl liquid medium are reported. The focus of the paper is to compare the behaviour of Stellite alloy 706 which contains 5 wt.% molybdenum with Stellite alloy 6 which contains 4.8 wt.% tungsten, both in cast and Hot Isostatically Pressed (HIPed) form, in terms of their electrochemical corrosion characteristics, their resistance to mechanical degradation and relationship between microstructure and degradation mechanisms. It has been shown that both cast and HIPed Stellite 706 possess better erosion and erosion–corrosion resistance than Stellite 6 counterparts under a wide range of conditions. The significant role of the microstructure and specifically the type of carbides in affecting the erosion–corrosion performance of the alloys is demonstrated and discussed. Also it has been shown that in these multiphase alloys there is no direct relationship between the hardness and erosion–corrosion resistance.