Application des UHTCs : Aéronautique et Aérospatial. Cas des composites ZrB2/SiC et HfB2/SiC

International audienc

Etude du système Fe-B-C : réactivité, acquisition de données thermodynamiques et modélisation

International audienc

The impacts of new processes

International audienc

Thermodynamic study of the U–Si system

International audienc

Oxidation resistance of Zr- and Hf-diboride composites containing SiC in air plasma up to 2600 K for aerospace applications

International audienceMicrostructure-controlled and fully-dense ZrB 2 and HfB 2 composites were elaborated by Spark Plasma Sintering with two different amounts of SiC (20 and 30 vol%) added to improve their oxidation resistance using optimized sintering parameters. Oxidation of several samples in air plasma conditions, at 1000 Pa total pressure and from 1800 K up to 2600 K, was carried out. The mass variation of samples during oxidation duration of 300 s on a temperature plateau was followed. A four-step oxidation mechanism, identified by four singular mass variation behaviors depending on the oxidation temperature ranges, was proposed and detailed. The total normal emissivity was measured on pre-oxidized samples and high values around 0.90 were obtained from 1300 to 1900 K due to the presence of the oxide layer formed in air plasma conditions and this high emissivity is interesting for aerospace applications

On the fabrication of ZrCxNy from ZrO2 via two-step carbothermic reduction-nitridation

International audienceProcessing parameters of a two-step carbothermal reduction–nitridation of ZrO2 as a UO2/PuO2 simulant to fabricate ZrN and ZrCxNy were examined. Variables studied were reaction time, reaction temperature and starting powder composition. Higher temperatures, longer reaction times and higher initial amounts of carbon in the starting material lead to increased nitridation similar to previous work with uranium oxide but reaction rate decreases with time. SEM and TEM of the reacted powders reveal regions of ZrC with ledges indicative of crystal defects with small particles of ZrN growing on the ZrC bulk material suggesting a reaction that occurs via Zr transport to the reaction site either through mass diffusion or evaporation–condensation of Zr(g) and with N2(g) forming the nitride. Annealing experiments on these mixed phases show formation of a solid solution which is rapid compared to the nitridation, where there is little to no formation of a solid solution

On the elastic modulus and hardness of co-sputtered Zr–Cu–(N) thin metal glass films

International audienc

Processing of (PyC/TiC) n multilayered coatings by pulsed CVD and RCVD

International audiencePyrocarbon/titanium carbide (PyC/TiC) n multilayered coatings have been deposited on carbon substrates by P-RCVD which is a combination of pulsed chemical vapour deposition (P-CVD) with reactive CVD (RCVD). From thermodynamic calculations, a thin TiC sublayer deposited between two PyC sublayers should be stoichiometric. TiC and PyC growth rates have been investigated, as well as PyC consumption occurring during carbide growth by P-RCVD. Hence, this process allows to achieve a sharp control of each sublayer thickness. Furthermore, it seems possible to totally consume the PyC intercalated between adjacent carbide sublayers in order to obtain a multilayered carbide (TiC) n. This method has been achieved to carbon fibre coating. The very first mechanical tests carried out on coated fibres are encouraging. The next step of this work lies in the study of such sub-micrometric coatings as interphases in ceramic matrix composites

Deposition and characterization of cold sprayed nanocrystalline NiTi

International audienc