Investigation of erosion-corrosion behavior of (WTi)C based weld overlays

Erosion-corrosion is responsible for severe damage and high maintenance costs in many industrial operations involving slurry handling such as oil sands and mineral processing. While tungsten carbide reinforced Ni-based alloy overlays are frequently used for applications requiring extremely high wear resistance, they tend to suffer from extensive carbide degradation during the weld cladding process which has been shown to severely impair their erosion-corrosion resistance. Recently, new (WTi)C based overlays are being developed to alleviate some of the limitations associated with the nickel-based tungsten carbide overlays. In this study, three different overlays reinforced with (WTi)C and one tungsten carbide were assessed using a slurry pot erosion-corrosion testing apparatus where the total erosion-corrosion (E-C) rate as well as the separate components of synergistic effect was determined. Erosion-corrosion test was performed at 30 °C, in an aqueous slurry containing 35 wt% AFS 50-70 silica sand and 3.5 wt% NaCl. A special SEM technique was employed to examine changes on the specimen surface at specific overlay locations before and after erosion-corrosion test in order to identify the effect of corrosion on erosion and vice-versa. It was found that tungsten is more prone to dissolution in the matrix during the welding process than titanium, which forms W-depletion/Ti-rich layer around the (WTi)C particle. Dissolution of tungsten and titanium promotes the formation of secondary carbides in the matrix. Erosion-corrosion performance of the overlays largely depends on increased fraction of retained primary (WTi)C phase.