Duplex structure formation and adherence properties of oxide scale on a metal

We present a model of the thermo-mechanical state of the oxide scale develo ped on a metallic substrate. The model is applied to the case of (111)Ni su rface oxidation. An analysis of the crystallography and the thermodynamics of the scale is performed. The calculated temperature-internal elastic fiel d diagram shows the possibility of oxidation regimes with the loss of elast ic continuity of the scale, which leads to the formation of a duplex struct ure. The resulting scale consists of the lower-ordered layer coherent with the substrate and the upper disordered layer, which is incoherent with the lower layer. The numerical modeling of the growth stresses together with th e residual stresses in the scale is presented. The calculated average stres ses after relaxation vary from 200 to -800 MPa (sigma(xx) component) and fr om 200 to -300 MPa (sigma(yy) component). The residual stresses vary from - 400 to -1400 MPa (sigma(xx)) and from -400 to -900 MPa (sigma(yy)). Calcula ted stress profiles shows the influence of the duplex structures parameters on the stress discontinuities. (C) 1999 Elsevier Science S.A. All rights r eserved.