Influence of the morphologic evolution of the eutectic carbides at high temperature on the thermal expansion behavior of refractory cast alloys

Two alloys particularly rich in carbides, a nickel-based one reinforced by chromium carbides and a cobalt-based one strengthened by tantalum carbides were characterized by metallography and their hardness and thermal expansion behavior tested, after alloys had undergone a more or less long aging treatment at high temperature. Aging induces a progressive coarsening and/or fragmentation of these interdendritic carbides, with as first consequence a decrease in hardness. Also due to these morphology changes, aging the alloys on long time leads to a loss of effect of the carbides on the thermal expansion behavior of the alloys. The total thermal expansion, initially lowered by the rigid carbides network, is then free again. Indeed, the high temperature phenomenon of plastic or viscous-plastic deformation in compression of the matrix by the initial continuous carbides network has almost disappeared. (C) 2010 Elsevier B.V. All rights reserved.