10376 Assessing the Erosion-Corrosion Processes of Metal Matrix Composites in Slurry Conditions by Electrochemical Techniques

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Product Number: 51300-10376-SG

ISBN: 10376 2010 CP

Author: J. F. Flores, A. Neville, N. Kapur, A. Gnanavelu

Publication Date: 2010

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The electrochemical behavior of metal matrix composites (MMCs) in static and under erosioncorrosion conditions is assessed in this paper. The MMCs studied are plasma transferred arc (PTA) overlays coatings which have a complex microstructure consisting of WC grains and secondary phases embedded in a matrix phase. The matrix materials are two nickel-based alloys (NiCrBSi and NiCrMoWB) and two iron-based alloys (FeCr and FeCrC). The objectives of this investigation were: a) to assess the corrosion mechanisms of the MMCs as a function of temperature, matrix phase composition and microstructure and b) to study the erosion-corrosion processes and regimes at different slurry conditions (temperature and solids loading). The static corrosion behavior was studied by potentiostatic polarization and changes in the corrosion mechanisms were established by analyzing the Arrhenius behavior. It was found that changes in temperature had a significant influence on the current density of the MMCs as expected. The Arrhenius plots of the MMCs show a double slope behavior which indicates that a two-steps corrosion mechanism takes place on the MMCs surface. Surface analysis after the static corrosion tests evidenced the presence of a selective degradation process affecting the interfacial zones between the matrix phase and the secondary phases formed during the solidification of the PTA overlays coatings. The effects of sand concentration and temperature are assessed by potentiostic tests and the critical conditions are established. The nickelbased MMCs show low current density values at sand concentrations below 0.5 g/l however, above that limit the current density values are dramatically affected. On the other hand, the iron-based alloys show high current density values even at low sand concentrations and a constant increase in current with sand concentration suggesting the process is activation controlled. In this paper, the degradation regimes are described as flow enhanced corrosion, erosion-corrosion and erosion-dominated processes based on the MMCs electrochemical response and supported by the surface analysis of the metal matrix composites.

Keywords: Metal Matrix Composites, erosion-corrosion, Arrhenius behavior, Slurry transportation