Effect of dendritic orientation on the high temperature oxidation kinetic of tantalum-containing nickel-base alloys

The aim of this work is the study of the possible effect of surface dendritic orientation on the high-temperature oxidation behavior of two chromia-forming Ni-base alloys with two tantalum contents (3%wt and 6%wt). Samples were prepared by special cutting orientation with regard to the external surface. Thermogravimetry tests were run at 1,000 °C, 1,100 °C and 1,200 °C and parabolic oxidation constants were determined taking into account the effect of the transient oxidation. When the sample surface is mainly parallel to the dendritic network, the oxidation parabolic constant can be higher than for a surface perpendicular to dendrites. It occurs only for temperatures that depend on the alloy. Inversely, the transient oxidation linear constant is generally higher for the perpendicular orientation than for the parallel one.