Thermodynamic model of oxide overgrowth on bare metals: Relaxation of growth strain by plastic deformation

A thermodynamic model has been developed which predicts the growth of either an initial (semi)coherent, strained crystalline oxide phase, or an initial amorphous oxide phase (with a possible amorphous-to-crystalline transition) on the bare single-crystalline metal substrate as a function of the metal substrate orientation, the growth temperature, and the oxide-film thickness. The model accounts for relaxation of residual stresses in a crystalline oxide overgrowth by plastic deformation (i.e., through the introduction of misfit dislocations at the metal/oxide interface). As an example, the microstructural evolution of the initial oxide film grown on the {111}, {110}, and {100} crystallographic surfaces of a bare Cr substrate has been modeled as a function of the growth temperature and the oxide-film thickness (<50.3em0exnm). The initial oxide-film growth on the bare Cr{100} and Cr{111} substrates is predicted to proceed by the initial formation and growth of an amorphous oxide film up to a critical thickness of about 0.5 and 0.90.3em0exnm, respectively. On the other hand, the onset of oxidation on a bare Cr{110} substrate should proceed by the direct overgrowth of a semicoherent, strained crystalline oxide film. These model predictions provide understanding for experimental observations reported in the literature.