HIGH TEMPERATURE OXIDATION AND HOT CORROSION BEHAVIOR OF NANOSTRUCTURED COATED INCONEL-718 SUBSTRATE

Abstract

High temperature corrosion is the degradation of metals and alloys owing to oxidation process at elevated temperatures, which is aggravated by a liquid salt deposit. The metals and alloys are subjected to degradation at much higher rates than in gaseous oxidation, with a porous, non protective oxide scale formed at their surface, and sulfides in the substrate. High temperature corrosion (hot corrosion) is a serious problem in power generation equipment, in gas turbines for ships and aircraft and in other energy conversion and chemical process systems e.g. in boilers, internal combustion engines, fluidized bed combustion. Hot corrosion is an accelerated corrosion, resulting in from the presence of salt contaminants such as Na2SO4, K2SO4, NaCl and V205. At higher temperature, deposits of Na2SO4 are molten (m.p. 884°C) and can cause accelerated attack on superalloys. For example, alloy components in gas turbine in aircraft, thermal power plant, land-based power generators, boilers, internal combustion engines, gas turbines and industrial waste incinerators undergo hot corrosion. No alloy is immune to high temperature oxidation and hot corrosion attack indefinitely, although there are some alloy compositions that require a long initiation time at which high temperature oxidation and hot corrosion process moves from the initiation stage to the propagation stage. Predicting corrosion of metals and alloys or coated alloys is often difficult because of the range of composition of the corrosive gaseous or molten environments and the variety of materials that may be used. In present study high temperature oxidation and hot corrosion behavior of Inconel 718 superalloy has been investigated with and without Nanostructured coatings. The TiA1N and A1CrN coatings were developed on superalloy by Physical Vapour Deposition technique. Coated and uncoated substrates were investigated by cyclic oxidation in air at 1000°C and 700°C. Hot corrosion test in conducted in molten salt environment at 700°C. The superalloys is procured from Mishra Dhatu Nigam Limited, Hyderbad (India). The -Inconel 718 is basically used for high temperature applications such as boilers and gas turbine parts, heat exchangers and piping in chemical industries and jet engines.