A pinboard by
Dr. Adam Khan

Associate Professor, Kalasalingam University, Tamilnadu India


Coatings and characteristic studies for gas turbine applications

The major requirement for the modern gas turbine engine is the improved efficiency. It is a most important challenge of the marine gas turbine engine toface and operate at aggressive corrosive environment and high erosive wear. These engines require high performance materials to exhibit maximum efficiency while operating at elevated temperatures. The hot section of the engine components are made of nickel based superalloys. The environment surrounded inside the engine components allows to undergo hot erosion and corrosion which is the conditional factor for the life of the gas turbine engines components.The thermal barrier coatings(TBCs) on superalloys increase the corrosion resistance. The ceramic top coat is to lower the thermal conduction and the metallic bond coat is to produce good adherence and to provide stress relaxation effects. Exposure to the operating temperature produces thermally grown oxides (TGO) at the interface of top coat and bond coat. But thethermally grown oxides induce the coatings to spall and deteriorate at the early stage. To overcome these problems, still the active research is going on to study the alloy development and coatings for corrosion protection which are under consideration.

In this research, the cyclic oxidation and hot corrosion behaviour of nickel alloy with TBCs are studied under mixed salt environment. The analyses are made with respect to the mass change per unit area and the characterisation studies are carried out through XRD analysis, optical image,SEM and EDAXanalysis of the oxide scales formed on the exposed surface. The cumulative mass change shows that the presence of molten salt mixture plays predominant role during hot corrosion. Consistency of oxide scale, rich in Cr2O3, NiO, Al2O3 and NiCr2O4 was confirmed through X-ray analysis. The results revealed that atelevated temperaturethe plasma coated alloy exhibits lower mass change than bare alloyMicrostructural analyses revealed enrichment of oxides with Ni, Cr and Mo on the surface of the samples at high temperature. There is no evidence on formation of intermediate oxide scale such as thermally grown oxides(TGO) in the coatings even after completion of defined corrosion studies.These coatings behave like a self-healing coating and it acts as a sacrificial layer to protect the substrate on prolonged exposure.