An experimental study of the erosion-corrosion behavior of plasma transferred arc MMCs

Handing highly concentrated slurries is a common occurrence in the mining, oilsands and fertilizers industries among others. The combination of erosive and corrosive processes due to the presence of sand and mineral particles flowing in a corrosive fluid produces a high degradation rate of the hydrotransport equipment. Hardfacing overlays such as metal matrix composites (MMCs) can be used to protect equipment subjected to an erosion-corrosion process. The combination of a ductile matrix and a reinforcing hard phase makes them good candidates for these applications. The erosion-corrosion behavior of two tungsten carbide (WC)-MMCs is studied in this paper. Two variations of the NiCrBSi matrix with different concentration of chromium (Cr), carbon (C) and boron (B) were evaluated with and without reinforcing hard phase. The erosion-corrosion behavior was evaluated as a function of sand concentration and temperature. To determine the influence of the mechanical degradation the study was conducted using I and 5 wt.% sand concentration. The overlays were evaluated at 20 and 65 degrees C and the velocity was kept at 14 m/s. Surface analysis was carried out to establish the degradation mechanisms after the erosion-corrosion tests. The two matrix materials showed differences in the microstructure, microhardness and erosion-corrosion resistance. The MMC with the harder matrix showed the lower mass loss and the erosive degradation was predominant in the overall erosion-corrosion process at the lower temperature. A different behavior was observed when the temperature of the testing solution was increased and a low sand concentration was used. Comparisons are made between the erosion-corrosion mechanisms of the two MMCs and the influence of the matrix in the overall degradation process is explained. (C) 2009 Elsevier B.V. All rights reserved.