Evaluation of young modulus of CVD coatings by different techniques

The silicon carbide (SiC) and pyrolytic carbon (PyC) thin films, deposited by Chemical Vapor Deposition in a fluidized bed, are used in the manufacture of nuclear fuels of high-temperature gas-cooled reactors. The integrity of these coatings ensures the absence of gas-coolant contamination. Therefore, it is important to be able to simulate the thermomechanical behaviour of these layers that involves the exact knowledge of the mechanical characteristics (fracture stress, Young modulus, Poisson's ratio, etc.). The elastic modulus of the SiC and PyC thin films has been evaluated by various techniques, at ambient and hot temperature (until 1600 degreesC). The studied mechanical tests are the nanoindentation, the acoustic microscopy and the impulse excitation technique. From these tests, the most adapted techniques have been discussed and defined, according to the nature of the layer, the temperature and the method of examination. This work is original because few comparative data exist in the literature for these kinds of layers. (C) 2004 Elsevier B.V. All rights reserved.