Effect of Edges and Corners on Stresses in Thermally Grown Alumina Scales

Residual stress near edges and corners of thermally grown alumina scaleswere investigated. In this study, an edge is the intersection of twoorthogonal flat surfaces and a corner is the intersection of three suchsurfaces. Microfluorescence measurements, performed on alloys withcomposition Fe–28Al–5Cr (at.%, bal. Fe) oxidized at 900°C,showed a large (>50%) reduction in hydrostatic stress in the vicinity ofedges and corners. Surprisingly, significant stress reduction persists outto distances twenty to fifty times the scale thickness from theedge. Finite-element analysis calculations confirm the experimental resultsand provide a considerably more detailed picture of the stress distributionand its components and show that much of the observed stress reduction nearan edge, is due to plastic deformation of the underlying metal.