Effect of a Preliminary Aging Treatment on the Oxidation Kinetic at High Temperature for a Cobalt–Based Alloy Strengthened by Tantalum Carbides

The purpose of this work is to examine if the behavior of refractory alloys in oxidation at high temperature can be influenced by the modification of the interdendritic carbides morphology due to a preliminary aging treatment at high temperature. A cobalt-based alloy strengthened by tantalum carbides was first exposed to 1200°C over a period of 100 hours, and characterized in high temperature oxidation, with samples cut in the middle of the alloy. Thermogravimetry runs were performed in air at 1000, 1100 and 1200°C during 50 hours, and the results were analyzed in order to specify the rates of transient oxidation, of parabolic oxidation and of chromia volatilization. The oxidized samples were metallographically examined. The fragmentation of the TaC carbides induced by the aging treatment tends to accelerate the oxidation kinetics in general, with higher values of parabolic and volatilization constants especially at 1200°C.