Abstrait

Influence of a preliminary aging treatment on the kinetic of oxidation at high temperature for a nickel-based alloy reinforced by chromium carbides

Patrice Berthod

The aimof thiswork is to examine if themodifiedmorphology of interdendritic carbides coarsened by an initial aging treatment can lead to a modified behaviour of the alloy in oxidation at high temperature. This was done here with amodelNi-30Cr-1.0Ccast alloywhichwas first exposed to 12000Cfor 5, 25 or 100 hours. Samples cut in the middle of the alloy were thereafter subjected to oxidation by air at 1000, 1100 and 12000C for 50 hours. The thermogravimetry resultswere treated in order to specify the rates of transient oxidation, of parabolic oxidation and of chromia volatilization (according to the lawmï‚´dm/dt = Kp-Kvxm), and finally of oxide spallation at cooling. The corresponding constants Kl, Kp and Kv were determined in all cases and they showed that oxidation rate and chromia volatilization rate increase with the preliminary aging durationwhile, in contrast, oxide spallation at cooling is delayed down to lower temperatures.