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Julien Sniezewski
Abstract
In situ investigation under thermal gradient of spallation of alumina-forming alloys and thermal barrier coatings
Julien Sniezewski - 16 December 2008
Spallation of the alumina layer grown at high temperature at the surface of the alumina forming alloy PM2000 or that of EB-PVD thermal barrier coatings (TBCs) coated on Ni based alloys is studied using a dedicated equipment specially designed in the laboratory. The equipment is capable of imposing a thermal gradient through the sample thickness in order to test the materials in conditions as close as possible to real service condition. The equipment has also the capacity to monitor in situ the spalling events that occur during the cooling phase of samples using high resolution camera, high speed camera or infrared camera. The analysis of images performed with a dedicated software allows a accurate description of the mechanisms of spallation during the successive cycles as well as the spallation kinetics or the morphology of the spalled particules.
The effects of various parameters on spallation are studied for alloy PM2000. Namely, a particular focus is placed on i) the surface roughness of the substrate ii) the oxide scale thickness, iii) the cooling rate, iv) the crystal orientation of grains, v) the number of oxidation cyles. The life of TBC is studied as a function of the oxidation temperature as well as the imposed thermal gradient. In addition, a attempt is made to determine the apparent toughness at the interface between the substrate and the TBC as well as its evolution with ageing time.
Keywords:
High temperature oxidation, spallation, alumina-forming, thermal
barrier coatings, thermal gradient, videometry, in situ
investigation.
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