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2592 |
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Thick YSZ coating on thin and smooth Haynes® 230 substrate: Use of suspension plasma sprayed coating as adhesive layer |
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Armelle Vardelle / University of Limoges-CNRS, France Romain Vert* / CEA , DAM, France Erick Meillot/ CEA , DAM, France Gilles Mariaux/ University of Limoges , SPCTS, France |
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The gas-cooled fast reactor is one of the next generation nuclear energy systems selected by the Generation IV International Forum. The reference design is a helium-cooled system operating at 7 MPa with an outlet temperature of 850°C.It requires high-temperature materials able to resist to depressurization accidents and loss-of-flow accidents linked to the high coolant pressure used to secure adequate heat transfer. Materials as Haynes®, could be protected by ceramic coating with specific properties to meet the specific conditions. In particular, coating must exhibit very high adhesion to the metal substrate. In plasma spraying which is a widely-used process to elaborate ceramic coatings for thermal barrier use, the adhesion of coatings is generally controlled by the roughness and cleanness of the surface. So, most of the plasma spray procedures involve the roughening of the surface by grit-blasting prior to deposition to adapt the roughness of the surface to the size of the sprayed particles. This surface preparation stage brings about compressive stresses that makes it difficult to use on thin substrates. The present works deals with the development of a coating system on 1-mm thick and smooth Haynes substrates. The system involves two layers: a bond coat, a few micrometers thick, made by suspension plasma spraying (SPS) and a topcoat, about 500µm thick, made by conventional plasma spraying. Yttria stabilized zirconia was used for both layers. SPS was investigated and optimized by using in-situ monitoring of the liquid feedstock and observation of single splats. Coating adhesion was determined by the Vickers Indentation Cracking technique and TEM observation of the interfaces. Also DRX, thermal diffusivity test and tensile test were performed on the coating system. |