Stresses induced in alloys by selective oxidation

Consider a substitutional solution of two metallic elements A and B. When the alloy is exposed to air at an elevated temperature, A oxidizes, but B does not. In the alloy, the two elements diffuse in opposite directions, but usually at different rates; the nonreciprocal diffusion is known as the Kirkendall effect. At the oxide-alloy interface, metallic atoms may either emit from or inject into the interior of the alloy. Both the nonreciprocal diffusion and the interfacial process generate stress in the alloy, while creep relaxes the stress. If tensile, this stress could generate voids. This paper formulates governing equations both in the alloy and at the interface. Numerical examples are given for nickel-aluminum alloys. The stress in the alloy near the interface can be either tensile or compressive, depending on the oxidation mechanism, as well as on the relative diffusion rates of Ni and Al. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.