Applications of High Velocity Oxy Fuel Spray Process for the Development of Slurry Erosion Resistant Coatings: An Overview

Erosion is a surface degradation phenomenon which affects the performance of hydraulic power plants, offshore oil and gas production industries, mineral processing and mining industries. In India alone the erosion problems cause a loss of the order of US$ 120 –150 million in a year for the hydro power stations. Erosion phenomenon mainly occurs in components handling flowing slurries, such as pump casings and impellers, stay and guide vanes, turbine blades, valves, elbows and tee junctions. A cost-effective way to improve the slurry erosion resistance of the components is by the application of thermally sprayed coatings. Among the various thermal spray coatings, High velocity oxy fuel (HVOF) coatings are very dense, strong and show low residual tensile stress or in some cases compressive stress. This enables very much thicker coatings to be applied than previously possible with the other processes. HVOF coatings are being exploited commercially to overcome the power loss arising due to excessive erosion of hydro turbines. In applications, where abrasive or erosive wear resistance is of primary importance, WC–Co with and without nickel or chrome is used.  HVOF cermet coatings of hard carbide phase tungsten carbide (WC) embedded in ductile matrix; typically coating system consisting of WC–Co, WC–Co–Cr, WC–Ni–Cr and FeCrAlY–Cr₃C₂ are being used in different industries for resisting the erosion phenomenon. In this paper an attempt has been made to describe HVOF thermal spray technology. Further this paper presents a survey of the research work done on the use of this technique to provide protection against erosion of some metals and alloys with a special emphasis on the hydraulic turbine steels.