Nanostructured CVD W/WC Coating Protects Steam and Gas Turbine Blades Against Water Droplet Erosion

Abstract

Gas turbine compressor blades operating with air inlet fogging can suffer from Water Droplet Erosion (WDE). WDE can also affect the last rows of steam turbines where expanding steam produces water condensation, especially under start-up and low load conditions. WDE damages the blades’ leading and sometimes trailing edges, increasing turbine rotation drag, reducing efficiency and leading to costly maintenance. This paper reports the testing of Hardide® nano-structured W/WC metal matrix composite coating as a protection against WDE. The Chemical Vapor Deposition (CVD) technology crystallizes the coating atom-by-atom from the gas phase and produces a uniform pore-free coating on complex shaped parts like turbine blades, vanes and pump impellers, including non-line-of-sight areas. Two variants of CVD W/WC coatings were tested: “A” type is 50–100 microns thick and has a hardness range of 800–1200 Hv and “T” type is 35–65 microns thick with a higher hardness of 1100–1600 Hv. Both coating types are made of Tungsten Carbide nanoparticles dispersed in metal Tungsten matrix. This composition and structure produce a combination of enhanced fracture toughness with high hardness and enables the deposition of exceptionally thick hard CVD coatings to provide durable protection against WDE and solid particle erosion. The coatings are pore-free thus also provide an effective barrier against corrosion. The coatings were tested for WDE resistance by the UK National Physics Laboratory (NPL) usin…