HIGH TEMPERATURE OXIDATION OF THERMAL BARRIER COATINGS WITH Ni- BASED BOND COAT

Abstract

Oxidation is the major source of degradation of metals and alloys subjected to elevated temperatures such as in energy generation and conversion systems like waste inclinators, boilers, power plants, IC engines and gas turbines. Therefore, for such exalted temperature applications, components manufactured from superalloys are used (which have excellent good mechanical strength and thermal stability, good corrosion and oxidation resistance) along with precautionary coat of Thermal Barrier Coating (TBC). The purpose of these coatings is to encase the components from large and protracted heat loads. In the present study, two commercially available A1203-13%TiO2 and A1203- 40%TiO2 coatings along with bond coat of Ni-20Cr were deposited on nickel based superalloy superni76 by Detonation-gun (thermal spray ) technique. 13oth the as-sprayed coatings and oxidized coating along with bare alloy were characterized by using SEM. X-ray diffraction and EDS. The experiments for study of cyclic oxidation were conducted for 50 cycles each at 700C, 800°C and 900°C. Every cycle consisted of 1 hour heating in furnace followed by 25 min cooling in still air. Weights of samples along with boat were taken after every cycle at each specified temperature to establish the kinetics of oxidation. Good oxidation resistance of coated samples was due to the presence of protective oxides such as Al2Ti05, A1203, Cr2O3 ,TiO2 etc. The A1203-13%TiO2 Coating showed good oxidation resistance as well as adherence better as compared to A1203-40%TiO2 and coating remained intact i.e no spallation was observed at 700°C as well as at 800°C.