Residual stress analysis with stress-dependent growth rate and creep deformation during oxidation
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onghua Zhangb) School of Science, Xi’an University of Science and Technology, Xi’an 710054, China
Xiaoxiang Yangb) School of Mechanical Engineering and Automation, Fuzhou University, Fuzhou 350108, China (Received 8 March 2016; accepted 27 June 2016)
In this paper, taking into account the external loading, growth strain, creep, and bending deformation during the metallic high-temperature oxidation, a residual stress evolution model is developed according to the force- and moment-equilibrium equations. In this model, oxidation kinetic relationship (the stress-dependent growth rate) is related to the stress in the oxide scale, not classical parabolic law. If and only if the stress in the scale or the activation volume is equal to zero, this relationship can reduce to the parabolic law. Then the stress-dependent oxidation kinetics is compared with the stress-independent one (the parabolic law). Finally, effects of the external loading on the stress distribution in the oxide scale, the curvature of the system and the scale thickness are discussed, and numerical results show that the tensile external loading decreases the oxidation stress and promotes the growth rate of the oxidation layer.
I. INTRODUCTION
When metals or alloys are subjected to an aggressive oxidizing environment at high temperature, the residual stress is inevitably generated.1–3 Furthermore, the stress distribution can influence the oxidation kinetics (i.e., growth of the scale). It is greatly important to determine the stress field together with the growth of the oxide film, and this is because the lifetime of high-temperature metals or alloys is controlled by the stress and the oxidation resistance. Generally speaking, the oxidation resistance depends on the mechanical properties of the forming oxidation scale whether it can prevent the underlying metal substrate from further oxidation. Evans4 pointed out that Alumima was often regarded as a barrier for oxygen diffusion because its oxide Al2O3 had excellent properties at high temperature, superior adherence, and slow growth rate compared with other oxides.5,6 The mechanism of the stress generation is not completely clear. Therefore, the stress analysis during oxidation has attracted more and more attention. At present, the main possible origins of the stress generation include: (i) epitaxy relationships between metal substrate and oxide scale (lack of compatibility of the crystalline lattices).7,8 The epitaxy is an interface Contributing Editor: Susan B. Sinnott a) Address all correspondence to this author. e-mail: [email protected] b) These authors contributed equally to this manuscript. DOI: 10.1557/jmr.2016.262
phenomenon and the growth of a thin layer on a substrate generally coincides with an incompatibility of the two crystalline lattices (i.e., lattice mismatch). Generally, the lattice parameter of an oxide is significantly larger than that of the metal. This large lattice mismatch9–11 makes the formation of coherent metal–oxide interface energetically unfavorable. Thus a mismatch strain nece
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