Long-range Interaction Between Solute Hydrogen Atoms And Different Dimensional Defects In Metallic Materials

Solute hydrogen atoms in metals may degrade the mechanical properties of metallic materials,leading to catastrophic failure and severe accidents.Considering the emergence of hydrogen corrosion in the nuclear industry,marine industry and other industries,as well as the increasing importance of developing hydrogen energy as clean energy,the study of hydrogen embrittlement phenomenon is of significance in engineering applications.Moreover,revealing the microscopic mechanism of hydrogen embrittlement is helpful to understand the influence of solute hydrogen atoms on the strengthening,plasticity and fracture behaviors of materials.Modern studies of hydrogen embrittlement consider that the interaction between solute hydrogen atoms and various defects in metals is an important factor leading to hydrogen embrittlement.In the framework of elasticity,by means of mesoscopic mechanics and Eshelby inclusion model,this thesis deeply studies the longrange interactions between solute hydrogen atoms and dislocation(line defect),inhomogeneity/crack/void(body defect)and bimaterial interface(plane defect)in materials,and investigates some possible microscopic mechanisms leading to hydrogen embrittlement.The main research contents and innovative works of this thesis include:(1)Based on the complex function representation of the plane problem of elasticity,the stress field induced by a solute hydrogen atom near a circular inhomogeneity in an infinite two-dimensional matrix is obtained.Through numerical calculations of solute hydrogen concentration distribution equation and shear stress induced by the solute hydrogen atmosphere acting on an edge dislocation,the influences of the solute hydrogen atoms on the interaction between circular inhomogeneity and edge dislocation are studied in detail.The results show that the inhomogeneity that is softer than the matrix has an attractive force on the solute hydrogen atom,while the inhomogeneity that is harder than the matrix has a repulsive force on the solute hydrogen atom;the elastic interaction between edge dislocation and inhomogeneity is partially shielded by the solute hydrogen atmosphere,which indicates that the solute hydrogen atoms weaken the second-phase strengthening in metals.(2)Based on the conformal mapping method and the complex function representation of the plane problem of elasticity,the stress field induced by a solute hydrogen atom near an elliptical void in an infinite two-dimensional matrix is obtained,and then the stress intensity factors at the finite-length sharp crack tips induced by a solute hydrogen atom are obtained.Through numerical calculations of solute hydrogen concentration distribution equation and stress intensity factors induced by the solute hydrogen atmosphere acting on crack tips,the influences of the solute hydrogen atoms on the finite-length sharp crack and the interaction between sharp crack and edge dislocation are deeply studied.The results show that whether the solute hydrogen atom has a shielding or anti-shielding effect on the crack tips depends on the position of the solute hydrogen atom;the solute hydrogen atmosphere gathered in front of the crack tips has a total anti-shielding effect on the crack tips and weakens the shielding effect of the edge dislocation on the crack tips,resulting in larger effective stress intensity factors at the crack tips than the applied ones.This makes the crack more prone to brittle propagation.Based on these results,a new hydrogen embrittlement mechanism,namely hydrogen induced crack anti-shielding,is proposed.(3)Treating the influence of solute hydrogen atoms as eigenstrains in the constitutive equations of elasticity and regarding the microstructures on the bimaterial interface as concentrated diffusive source,concentrated forces and concentrated dislocations,the interaction between the solute hydrogen atoms and a transversely isotropic bimaterial interface is deeply studied based on the series transformation method of vector function system.The results indicate that there is a high concentration of solute hydrogen near the bimaterial interface;the local stress state near the bimaterial interface is greatly changed by the solute hydrogen atoms;the stress and displacement fields on the two sides of the bimaterial interface have different distributions.These conclusions can help to understand the corrosion and damage caused by solute hydrogen near the bimaterial interface.(4)Considering that the continuous description needs to assume a very high initial hydrogen concentration which is nearly impossible to reach in real materials,a threedimensional discrete description of solute hydrogen atmosphere has therefore been developed based on the statistical mechanics.Monte Carlo simulation method is used to obtain the discrete steady-state distribution of solute hydrogen atmosphere.The interaction between the solute hydrogen atoms and a spherical void in a spherical elastic solid is thouroughly studied,and the influence of temperature on the distribution of solute hydrogen atoms is analyzed.The results show that at low temperatures,the system of solute hydrogen eventually reaches a metastable equilibrium state and the solute hydrogen atoms tend to form solute clusters near free surfaces.In constrast,at higher temperatures,the solute hydrogen atoms tend to be uniformly distributed,which indicates that the temperature has an important effect on the distribution of solute hydrogen.The present work has paved the pathway to further explore the interaction between solute hydrogen atoms and various defects in metallic materials in the framework of discrete description.