Study On The Interaction Of Solute Hydrogen Atoms And Typical Defects

Hydrogen has attracted more and more attention due to its high calorific and no pollution as clean energy.Hydrogen can be easily adsorbed on the surface of the carrier and dissolved into metals during storage and transportation,leading to the reduction of the mechanical properties of the carrier and even catastrophic fracture.This effect of destructing the mechanical properties of the material due to hydrogen is called hydrogen embrittlement,which hampers the use of hydrogen energy.Hydrogen embrittlement is also common in various industries,such as the chemical industry,slip and offshore engineering,offshore drilling platforms,power,etc.Therefore,over the past 150 years,more and more attention was paid to hydrogen induced failure mechanism,and various hydrogen embrittlement mechanisms were proposed,including hydride formation and fracture mechanisms,hydrogen enhanced decohesion mechanism,hydrogen enhanced local plasticity mechanism,etc.However,at present,no mechanism is universally applicable.With the rise of new hydrogen energy,the mechanism of brittle fracture caused by hydrogen has been paid more attention from academia and industry.In the study of hydrogen embrittlement mechanism of metals,the core scientific question that must be answered is:how does the solute hydrogen atom interact with the internal defects of metal materials(such as microcracks,micro-voids,dislocations,etc.)?From a microscopic scale,in-depth study of the interaction between solute hydrogen atoms and internal defects in metals has important theoretical significance for revealing the physical mechanism of hydrogen-induced embrittlement,and has potential application in guiding the design of materials against hydrogen embrittlementIn this thesis,the interaction between solute hydrogen and surface notch/crack and edge dislocations is studied,respectively.In order to simplify the problem,only two-dimensional model is considered here,and the solute hydrogen is treated as a dilatation line.The interaction between solute atom and surface crack in isotropic material is studied using the classical linear elasticity theory and elastic complex function theory.The image stress field caused by surface crack is derived.The effects of crack depth and radius of curvature of crack tip on the stress field are discussed.Then the displacement and stress fields caused by solute atom in anisotropic material were studied with Stroh theory,and the Peach-Koehler force generated by the solute atom induced stress field on the edge dislocation was derived.Some main conclusions by this study are as follows:Surface cracks have strong effects on the stress field of solute atom.Compared with the stress field of solute atom in an infinite medium,the symmetry of the stress field of solute atom in infinite media disappears due to the image effect of surface crack,and the stress near the edge of the crack increases significantly.The characteristic geometry lengths of the crack(depth and radius of curvature)have heavy influence on the stress field of solute hydrogen atom.The interaction between hydrogen and notch/crack depends on the position of the hydrogen atom with respect to the notch/crack tip.The solute atoms may have shielding,anti-shielding or no effect on the crack tip,depending on the different angles of the solute atoms with respect to the crack tip.The displacement field and stress field induced by hydrogen dilatation line in the anisotropic materials are obviously different from those in the isotropic ones.The displacement field and stress field due to hydrogen dilatation line in the anisotropic materials are still inversely proportional to the radial distance r and r~2,respectively,but they are related to the circumferential angleq,different from those fields in the isotropic materials.The stress field of dilatation line in the anisotropic materials depends upon the stiffness matrix of anisotropic materials and shows periodicity and symmetry.Moreover,in the anisotropic materials,the hydrostatic stress induced by dilatation line is not zero(?_H?0),and thus there is an obvious interaction between solute atoms;however,in the isotropic materials,the hydrostatic stress induced by dilatation line is zero(?_H=0)and thus there is no long-term interaction between solute atoms.The interaction between hydrogen dilatation line and edge dislocation in the anisotropic materials is significantly different from that in isotropic materials.In anisotropic materials,the Peach-Koehler force on the edge dislocation due to the stress field of dilatation line changes periodically with the angle of the position of the edge dislocation with respect to the dilatation line,but in the isotropic materials,the Peach-Koehler force does not change.