Elastic deformation of alumina scale has been revealed. Scanning Electron Microscopy observations shows convoluted layer next to planar relaxed scales. Finite Element Modeling (F.E.M.) calculation has been performed in order to evaluate the intensities of local stresses consistent with the observed microscopic deformations. Local plastic deformation of the substrate at the anchoring points of the substrate to the oxide layer has been also showed up. The effect of substrate grain crystallographic orientation on underscale voids shape and on spalling mechanism is presented. Substrate's voids surfaces under the scale together with the oxide inner surface have been detailed in order to explain the growth and spallation phenomenon.