Erosion, Corrosion and Erosion-Corrosion of EB PVD Thermal Barrier Coatings
نویسندگان
چکیده
Electron beam (EB) physical vapour deposited (PVD) thermal barrier coatings (TBCs) have been used in gas turbine engines for a number of years. The primary mode of failure is attributed to oxidation of the bondcoat and growth of the thermally grown oxide (TGO), the alumina scale that forms on the bondcoat and to which the ceramic top coat adheres. Once the TGO reaches a critical thickness the TBC tends to spall and expose the underlying substrate to the hot gases. Erosion is commonly accepted as a secondary failure mechanism, which thins the TBC thus reducing its insulation capability and increasing the TGO growth rate. In severe conditions erosion can completely remove the TBC over time, again resulting in the exposure of the substrate, typically Ni based superalloys. Since engine efficiency is related to turbine entry temperature (TET) there is a constant driving force to increase this temperature. With this drive for higher TETs comes corrosion problems for the yttria stabilised zirconia (YSZ) ceramic topcoat. YSZ is susceptible to attack from molten calcium magnesium alumina silicates (CMAS) which degrades the YSZ both chemically and micro-structurally. CMAS has a melting point of around 1240oC and since it is common in atmospheric dust it is easily deposited onto gas turbine blades. If the CMAS then melts and penetrates into the ceramic, the life of the TBC can be significantly reduced. This paper discusses the various failure mechanisms associated with the erosion, corrosion and erosion-corrosion of EB-PVD thermal barrier coatings. The concept of a dimensionless ratio D/d, where D is the contact footprint diameter and d is the column diameter, as a means of determining the erosion mechanism is introduced and discussed for EB PVD TBCs.
منابع مشابه
Some Observations on Erosion Mechanisms of Eb Pvd Tbcs
Following the successful application of Electron Beam (EB) Physical Vapour Deposition (PVD) Thermal Barrier Coatings (TBCs) to moving parts of turbine engines the erosion resistance of these coatings has been of interest among researchers. However, although there are a number of papers on the erosion rate of these coatings, little has been reported on their erosion mechanism. This paper provide...
متن کاملA MONTE CARLO MODEL FOR PREDICTING THE EROSION RATE OF EB PVD TBCs
Since the introduction of electron beam (EB) physical vapour deposition (PVD) thermal barrier coatings (TBCs) and their application to moving components in the hot gas stream, erosion has become a prime concern. EB PVD TBCs, due to their unique columnar microstructure are far more strain tolerant than their plasma sprayed (PS) counter parts and can thus be used under more exacting operating con...
متن کاملThermal Conductivity Analysis and Lifetime Testing of Suspension Plasma-Sprayed Thermal Barrier Coatings
Suspension plasma spraying (SPS) has become an interesting method for the production of thermal barrier coatings for gas turbine components. The development of the SPS process has led to structures with segmented vertical cracks or column-like structures that can imitate strain-tolerant air plasma spraying (APS) or electron beam physical vapor deposition (EB-PVD) coatings. Additionally, SPS coa...
متن کاملSynergistic effect of ultrasonic cavitation erosion and corrosion of WC-CoCr and FeCrSiBMn coatings prepared by HVOF spraying.
The high-velocity oxygen-fuel (HVOF) spraying process was used to fabricate conventional WC-10Co-4Cr coatings and FeCrSiBMn amorphous/nanocrystalline coatings. The synergistic effect of cavitation erosion and corrosion of both coatings was investigated. The results showed that the WC-10Co-4Cr coating had better cavitation erosion-corrosion resistance than the FeCrSiBMn coating in 3.5 wt.% NaCl ...
متن کامل