Stress development in alumina scales formed upon oxidation of (111)NiAl single crystals

Stress evolution in the a phase of the alumina scale formed on single crystals of (111) NiAl as a function of oxidation time at 1100 degrees C is reported. The measurements are made at room temperature using the fluorescence from trace Cr3+ impurities in the NiAl that are incorporated into the oxide scale during oxidation. After a short transient period, the room-temperature stress is essentially independent of oxidation time. At all oxidation times, there exist large stress gradients through the scale thickness, indicating that either fresh oxide is formed nonuniformly through the thickness of the growing scale or stress relaxation occurs non-uniformly. (C) 1997 Elsevier Science Ltd.