Considerations regarding WC-cermets depositions by HVOF and ESD techniques used for reinforced steel components for geothermal turbines

Abstract

Abstract The cumulative effect of erosion-corrosion process in geothermal turbines results in significant damages, especially for rotors and turbine blades; the degree in which they are affected depends on steam temperature, mechanical impact and the geothermal composition of the substances dissolved in steam. Layer composite materials are a feasible option to improve the erosion-corrosion resistance and the durability of turbine components. There cermet powders containing tungsten carbide are used for High Velocity Oxy-Fuel (HVOF) spaying and for Electro Spark Deposition (ESD) to obtain graduate microstructure and to form local hard structures. Both techniques by WC-cermet depositions were found to be most suitable to improve wear resistance, to repair rotors and blades and to provide possible life extension of geothermal turbines. The paper presents a comparative assessment of tungsten carbide and the technological parameters used for HVOF and ESD cermets layers depositions. Also, the work presents the analysis of the micro chemical composition of the microstructure, the micromechanical characterization and erosion-oxidation resistance of HVOF and ESD coatings using WC-cermets on steel substrates. The experimental procedure involved X-ray diffraction of the samples, micro mechanical tests and SEM investigations to provide specifically information about micro-morphological modifications and grade of adhesion of protective layers.