DEVELOPMENT OF EROSION RESISTANTSURFACE COATINGS ON STEEL COMPONENTS

Abstract

Solid particle erosion is a major problem in hydro and steam turbines. Heavy damages of under water parts in hydroelectric projects due to hard silt particles are responsible for serious erosion problems. In the steam turbines, this is mainly due to the formation of magnetite on the inside of boiler tubes. This builds up, travels along with steam causing erosion in the areas where steam velocities are higher. So, to protect the base material from erosion, thermal spray coatings are used. In this work the martensitic stainless steel and austenitic stainless steel substrates are coated with 86WC-lOCo-4Cr, 75Cr3C2-25NiCr and 100%A1203 using detonation gun spray technique. Plasma spray technology is also used for coating the martensitic stainless steel substrate with 86WC-lOCo-4Cr. Optical microscopy, chemical analysis, micro hardness testing, X-ray diffraction, porosity testing have been carried out for the characterization of coatings. The erosion test is carried out using air jet erosion tester with silica erodents at a velocity of 60m/s at 900 impact angle. From the experimental results it is observed that 75Cr3C2-25NiCr coating shows improved erosion resistance on martensitic stainless steel and 86WC-l0Co-4Cr coating shows high performance with austenitic stainless steel. A comparison is also made between the detonation gun coated and plasma spray coated 86WC-l0Co-4Cr coatings on martensitic stainless steel. The scanning electron micro structural details 'of eroded samples have been carried out to ascertain the mechanisms of erosion.