Thermal Shock and Oxidation Stability Tests to Grade Plasma Sprayed Functionally Gradient Thermal Barrier Coatings

Pasupuleti Kirti Teja Pasupuleti Kirti Teja,Parvati Ramaswamy,Narayana Murthy S.V.S

doi:10.34256/famr1911

Pasupuleti Kirti Teja Pasupuleti Kirti Teja, Parvati Ramaswamy + Show 1 more

Open Access

https://doi.org/10.34256/famr1911

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Abstract

Functionally graded layers in thermal barrier coatings reduce the stress gradient between the overlaid ceramic coatings and the underlying metallic component. Introduced to alleviate early onset of spallation of the coating due to thermal expansion mismatch, this facilitates improvement in the life of the component. Conventional thermal barrier coatings typically comprise of duplex layers of plasma sprayed 8% yttria stabilized zirconia (ceramic) coatings on bond coated (NiCrAlY) components/substrates (Inconel 718 for example). This work highlights the superiority of plasma sprayed coatings synthesized from blends of the intermetallic bond coat and ceramic plasma spray powders on Inconel 718 substrates in three-layer configuration over the duplex layered configuration. Assessed through (a) thermal shock cyclic tests (at 1200oC and 1400oC) in laboratory scale basic burner rig test facility and (b) oxidation stability test in high temperature furnace (at 800oC and 1000oC) the functionally graded coatings of certain configurations exhibited more than double the life of the conventional 8% yttria stabilized zirconia duplex (double layer) coatings. Micro- and crystal structure analysis support the findings and results are detailed and discussed.

Highlights

Atmospheric Plasma spraying (APS) is a wellmaterials, applied on metals to make their surfaces thermally established method to fabricate Thermal Barrier Coatings (TBCs) with yttria
TBCs thicknesses are in the range of 120μm - 250μm which thermal expansion characteristics of the ceramic materials are comprised of low thermal conductivity material layer and underlying base metal results in poor adhesion between with suitable adhesion characteristics and microstructures the metal ceramic interface especially in service at high
The substrates were blasted with alumina grits, degreased with a solvent following which bond coat was deposited on the surface over prior to the plasma spray coating of the Functionally Graded Materials (FGMs) layers

Summary

Introduction expansion mismatch between the metal substrate and

1.1 Thermal Barrier Coatings ceramic over layer [5]. Atmospheric Plasma spraying (APS) is a wellmaterials, applied on metals to make their surfaces thermally established method to fabricate TBCs with yttria Coat i.e. 8YSZ and NiCrAlY respectively) layers with gradually varying thermal expansion characteristics This is Another method involves blending of the done via combination of two or more different types of constituent powders such as the bond coat and ceramic top coating materials, with optimized coating characteristics coat in desired proportions [18]. Upon establishing the most strong potential for decreasing damage due to mis-match in suited blend configuration, that particular FGM may be properties amongst the TBC and the substrate This is because synthesized by pre-alloying the feedstock powder prior to the interfacial layers allow smooth transition of properties plasma spraying [16, 20]. The capability of the intermediate layers in alleviating the stresses and to prolong the life of the (i) First coated layer on grit blasted surface: BC: 75 μm TBC system was being explored in this work

Oxidation Stability Test

Microstructure and Structural phase analysis

Results of FGM layer between the bond coat and ceramic coat layers

Conclusions