Sol–gel thermal barrier coatings: Optimization of the manufacturing route and durability under cyclic oxidation

Abstract

OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao.univ-toulouse.fr/ Eprints ID : 4750 A new promising and versatile process based on the sol-gel transformation has been developed to deposit yttria-stabilised thermal barrier coatings. The non-oriented microstructure with randomly structured pore network, resulting from the soft chemical process, is expected to show satisfactory thermo-mechanical behaviour when the TBC is cyclically oxidized. First stage of the research consists of optimizing the processing route to generate homogeneous microstructure and controlled surface roughness. The objective is to reduce, as much as possible, the size and depth of the surface cracks network inherent to the process. Indeed, the durability of the TBC when cyclically oxidized strongly depends on the sharpness of those cracks that concentrate thermo-mechanical stresses and generate detrimental propagation resulting in spallation. Cyclic oxidation tests are performed using a cyclic oxidation rig instrumented with CCD cameras to monitor in a real time basis the mechanism of crack propagation and spallation. The impact of various parameters either directly related to the processing route, e.g. the intimate microstructure of the TBC and the TBC thickness, or to the thermal loading, e.g. the oxidation temperature and the cumulated hot time, on the durability of the TBC is investigated.

Outstanding durability of sol-gel thermal barrier coatings reinforced by YSZ-fibers

“…As a remark, it has been proved that sol gel thermal barriers fabri cated from aerogel are subjected to delamination in the form of islands [11,30] whereas the delamination of thermal barriers made by EBPVD occurs by the loss of large ceramics pieces [5,31,32]. Thus, the de gradation mode of fiber based thermal barriers approaches the degradation mode of EBPVD systems with delamination of large spalls of coating.…”

Feasibility of luminescent multilayer sol-gel thermal barrier coating manufacturing for future applications in through-thickness temperature gradient sensing

“…8.b). The isotropic nature of the resulting porosity is believed to provide a good balance between thermal insulation and thermomechanical strength [13,14,44].…”

Reinforced sol–gel thermal barrier coatings and their cyclic oxidation life

“…8,9 An attempt is made to model the mechanisms of YSZ detachment from the substrate surface during the oxidation cycles and differentiate the behaviour of non-reinforced (Fig. 8a) and reinforced TBCs (Fig.…”

“…This should result in an attractive compromise between thermal conductivity and mechanical strength. In a previous paper, 8 the mechanisms responsible for the damage of sol-gel coatings subject to cyclic oxidation was identified and discussed as a function of the oxidation temperature and the TBC thickness. Initially, the degradation of sol-gel TBCs proceeds through the formation of a regular crack network occurring, either during the post-deposition thoroughly controlled by thermal treatment or during the very first cycles of oxidation, in both cases as the result of the thermally-activated sintering of the zirconia deposit.…”