TOPPCOAT - Towards Design and Processing of Advanced, Competitive Thermal Barrier Coating Systems
Overview
Background & policy context:
The target was to develop more reliable, less expensive Thermal Barrier Coatings (TBCs) with increased lifetimes and improved temperature capability. The top coat of TBC systems consists of a low thermal conductivity material such as yttria stabilised zirconia (YSZ). This can be thermally sprayed by means of air plasma spraying (APS) or deposited by (more expensive) electron beam physical vapour deposition (EB-PVD). The PVD process leads to a columnar microstructure giving the coating a high strain tolerance, and a greater lifetime and reliability than plasma-sprayed TBC systems.
Objectives:
The major objective of the project is the development of improved TBC systems using advanced bonding concepts in combination with additional protective functional coatings. The first specific objective will be to use these developments to provide a significant improvement to State-of-the-Art APS coatings and hence provide a cost-effective alternative to EB-PVD.
The second objective will be to combine these new concepts with new coating technologies to provide new, advance material for thermal barrier systems with a capability exceeding the performance of EB-PVD coatings.
In both cases, a major impact on TBC performance, manufacturing and maintenance costs and hence competitiveness of European aviation gas turbine manufactures is expected.
Methodology:
- Work package 1
To have a large database, the consortium decided to prepare 21 different TBC systems consisting of different bondcoats and topcoats. To compare the new specimen with state of the art TBCs, also an APS reference and an EB-PVD reference were produced. Beside the standard materials like spray dried YSZ, advanced materials like nano sized YSZ suspension and YSZ precursor in CVD processes were used. For all coating materials, detailed specifications were defined. Furthermore, the substrate material for the different TBC was defined, and samples from raw material like CMSX4 and IN738 were produced. For special geometries, hollow cylinders and massive pins were manufactured via electrical discharge machining. - Work package 2
The main objective was the production and procurement of powders and precursors. A large batch of fused & crushed YSZ powder was supplied by TIAG, and SM provide a large batch of spray dried YSZ powder. Besides these conventional materials, a YSZ powder with a small amount of Rare Earth was produced in order to use this material as sensor coating material. Further, a YSZ suspension with agglomerated, nano sized particles was developed and optimised by TIAG in collaboration with FZJ. Three batches of fused and crushed magnesia alumina spinel with slightly different contents of Al2O3 were produced also by TIAG. ONERA tested different precursor as starting material for PE-CVD coatings. - Work package 3
As mentioned in the project description, one route to achieve more strain tolerant coatings was the application of 3D interfaces on substrate surfaces. This surface modification was realised by using laser cladding technique. With this method it was possible to produce thin bars on the surface with a height of about 500µm. - Work package 4
This was the largest work package in the project. The main objective was the development of strain tolerant coatings with different approaches to achieve this aim. The performed work can be divided into the following categories:- Development of TBC with segmentation crack densities of about 10 cracks mm-1 using advanced conventional plasma spraying technique;
- Development of TBC systems using new materials like nano sized powders;
- Development of TBCs with columnar microstructure using new techniques like LPPS-TF, PE-CVD.
Altogether, at the end of WP 4 more than 280 test samples with 4 differen
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