P. Berthod, T. Schweitzer and L. Aranda
University of Lorraine, Lorraine, France
Keywords: cast superalloys, zirconium carbides, high temperature creep, high temperature oxidation
Zirconium is a MC carbide-former element able to give superalloys potential high strength at high temperature. As many MC carbides, eutectic ZrC may precipitate at solidification with high imbrication with the matrix and they are very stable at elevated temperatures. They are thus possibly very efficient for the strengthening of alloys needing high resistance to creep deformation at high temperature. ZrC are rarely used for this the purpose and this work aims to test this strengthening solution in refractory cobalt-based alloys. Several Co-based alloys of the {Co-25Cr-xC-yZr}-type were cast and they underwent DTA measurement for specifying their melting range. Flexural creep tests (1200°C, 20MPa) and oxidation runs in synthetic air at 1200°C were carried out. The microstructures of the obtained alloys are composed of a dendritic matrix and of a dense interdendritic network of carbides, constituted of mainly ZrC. These ones effectively display a script-like shape resulting from eutectic solidification. The obtained temperatures of melting start are very high in most cases. The observed creep resistances are really interesting but the behaviors in high temperature oxidation need to be significantly improved.