Cracking and spalling of protective oxide layers

Abstract

This paper discusses the role of thermal stresses on the mechanical integrity of oxide layers. It is shown that the processes of cracking and spalling of oxides differ depending on the stress state (tensile or compressive) and on the relative strengths of oxide and oxide-metal interface. Under tensile conditions, through-thickness cracks develop from pre-existing defects in the oxide layer and these generate shear stresses along the interface which may result in decohesion. Under compressive conditions, spallation may result either from the growth of a tensile, wedge crack along the interface or by buckling and cracking of the oxide layer. Initial results of a finite element analysis are provided for both mechanisms.