Decohesive Concept of the Interaction of Hydrogen with Metals
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DECOHESIVE CONCEPT OF THE INTERACTION OF HYDROGEN WITH METALS V. V. Panasyuk
UDC 539.4.01; 539.4.019.3
We consider some concepts of the interaction of hydrogen with metals (iron and its alloys) under loads in hydrogen-containing media and, in particular, their hydrogen embrittlement. This problem is analyzed in numerous works, where different concepts and models are proposed for the substantiation of the mechanisms of hydrogen embrittlement of metals. However, these concepts do not enable us to understand the dual character of the action of hydrogen on the deformation of metals, i.e., the facilitation of their plastic deformation and embrittlement. We describe the decohesive concept of hydrogen–metal interaction based on which it is possible to explain the processes of plasticization of metals in the initial stage of deformation and their embrittlement in the course of subsequent deformation. We also present a survey of investigations in this direction carried out by researchers of the Karpenko Physicomechanical Institute of the Ukrainian National Academy of Sciences. Keywords: metallic materials, hydrogen, deformation, hydrogen decohesion of interatomic bonds, plasticization and embrittlement of metals, crack resistance.
Introduction Elements of structures and buildings always operate in contact with media. In numerous cases, these media contain hydrogen. Hydrogen-containing media of this kind are used in metallurgy, chemistry, and power engineering. Hydrogen penetrates into the metal through the surface or is present in it and affects its physicomechanical characteristics. Thus, hydrogen decreases the plasticity of macrovolumes, yield limit, and ultimate strength or facilitates the process of plastic deformation of the metal in the initial stage of deformation. Therefore, it is important to determine the effect of hydrogen on the physicomechanical properties of metals and develop methods for the evaluation of the characteristics of their resistance to fracture (crack propagation) in order to determine the serviceability of structural elements in given hydrogen-containing media. In the middle of the last century, the results of investigations in this field were analyzed fairly comprehensively [1–17]. It is worth noting that the development of this direction of materials science was caused, to a significant degree, by the use of achievements of the fracture mechanics of deformable solids with cracklike defects (sharp stress concentrators) and by the development of the concept of physicochemical situation formed near the crack tip in the deformed body operating in contact with media penetrating into the vicinity of the tip [18, 19]. Since, in the process of operation of machines and buildings, it is impossible to neglect the possibility of appearance of cracklike defects in the materials of structures, the indicated concept of physicochemical situation near the crack tip, i.e., in the process zone with penetrated hydrogen, becomes especially important. Just the changes in this situation under the action of hydrogen
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