Evaluation of Adhesive Strength of Oxide Layer on Carbon Steel at Elevated Temperatures
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1215-V16-22
Evaluation of Adhesive Strength of Oxide Layer on Carbon Steel at Elevated Temperatures Manabu Satou Department of Quantum Science and Energy Engineering, Tohoku University, 6-6-01-2, Aramaki-aza-Aoba, Sendai, 980-8579, JAPAN ABSTRACT Adhesive strength of the oxidation layers on carbon steel was evaluated by means of a laser shock method, which uses a pulsed laser to generate shock wave. Oxidation for 200 hours in air created 10-micron-thick magnetite on carbon steel. Typical strength of the layer was evaluated to be about 50MPa at ambient temperature. The adhesive strength was varied from around one-tenth of yield stress to the ultimate tensile strength of the base materials. The adhesive strength of the oxide layer depended on test temperature. It is possible that the adhesive strength becomes an essential parameter for the evaluation of the protective layers. INTRODUCTION Adhesive strength of the layers that protect from corrosive environments for structure materials in nuclear systems including fusion and fission reactors is of interest not only from fundamental point of view but also engineering point of view, because the protective function of the layer is effective when the layers maintain on base materials with suitable strength. For example, although lead-bismuth eutectic coolant in fast reactor design provides superior advantages from view points of neutronics and safety issue, severe corrosion of structure material is one of the key issues to be solved[1]. Formation of the protective oxide layer depends on oxygen potential in lead-bismuth as the coolant material and on chemical composition of steel as the structure material. It has been demonstrated that the contents of chromium in the steel promote the formation of stable oxide layer. Once oxide layers were formed on the surface in the coolant material, corrosion behavior changed from the liquid metal corrosion to the oxidation corrosion [2,3]. Formation of stable chromium-rich oxide layer is believed to prevent break away of the oxide layer. Stability of the oxide layer from a view point of the thermodynamics is important as well as the mechanical properties of the oxide layer including adhesive properties against the base material. In this paper, an attempt was carried out to evaluate the adhesive property of the protective coating layer on the structure materials, as for a simple example, oxidation layer on a carbon steel was examined. EXPERIMENTAL Evaluation method of the interface strength depends on degree of the applied stress and its mode such as shear, tensile or compression. Environment like temperature and atmosphere will affect the evaluation method. Frequency of the stress and temperature cycles and duration of the applying stress will affect its fracture modes such as impact fracture or creep failure. Integrity of the interface depends on manufacture procedures. Resultant secondary stress due to differences of the thermal expansion also affects the interface properties. In this paper, to simplify the applied stress condition, e
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