Abstract
Corrosion damage of materials operating in the harsh geothermal environment with corrosive species, high temperatures and pressures necessitate the development of novel, cost-effective corrosion-resistant coatings to extend the service life of down-hole drilling equipment and power plant components. The thermal spraying process is a well-established and versatile method for producing thick coatings in terms of cost, wide range of powder selection, and high deposition efficiency. High Velocity Oxygen Fuel (HVOF) thermal spraying process has proven to be one of the most effective techniques for deposition of conventional cermet-carbide composite coatings improving their high-temperature oxidation corrosion, erosion, and wear resistance. The objective of this work focuses on testing the corrosion resistance of a CoCrFeNiMo0.85 high entropy alloy (HEA) coating fabricated by HVOF technique. Here we report the comparative analysis of corrosion resistance for the developed CoCrFeNiMo0.85 and CrC–NiCr, WC–Co carbide systems. The HEA and Cermets were immersed for 14 days in a simulated alkaline geothermal drilling environment at 120 °C and 50 bar. In addition, an electrochemical-accelerated corrosion test in a 3.5wt% NaCl was carried out at ambient temperature to investigate the behavior of the coatings in the presence of Cl-ions. The compositional effect of the microstructure on corrosion performance of the tested samples is discussed by analyzing corrosion damages and products using SEM/EDS analytical methods. The findings are essential to determine the suitability of HVOF as a fabrication method for CoCrFeNiMo0.85 HEA coatings and the candidacy of the resulting coating for corrosion protection of components used in geothermal energy production.
