Abstract
Tensile stress relaxation is combined with transmission electron microscopy to reveal dramatic changes in dislocation structure and sub structure in pure α-Fe as a result of the effects of dissolved hydrogen. We find that hydrogen charged specimens after plastic deformation display a very characteristic pattern of trailing dipoles and prismatic loops which are absent in uncharged pure metal. We explain these observations by use of a new self consistent kinetic Monte Carlo model, which in fact was initially used to predict the now observed microstructure. The results of this combined theory and experimental study is to shed light on the fundamental mechanism of hydrogen enhanced localised plasticity.
Highlights
Tensile stress relaxation is combined with transmission electron microscopy to reveal dramatic changes in dislocation structure and sub structure in pure α-Fe as a result of the effects of dissolved hydrogen
Specific new features of the model are, (i) simultaneous kink nucleation, migration and hydrogen jumping; (ii) kink pair formation energy affected by all hydrogen within the core; (iii) a non equilibrium distribution of hydrogen which depends on temperature and average dislocation velocity; (iv) kink pair formation energy depends on average dislocation velocity; (v) mobile hydrogen during glide— the total hydrogen occupancy within the core is assumed fixed
Scanning Transmission Electron Microscopy (STEM) was preferred over transmission electron microscopy (TEM) for imaging dislocations as it is better able to resolve individual dislocation lines in dense dislocation walls
Summary
Tensile stress relaxation is combined with transmission electron microscopy to reveal dramatic changes in dislocation structure and sub structure in pure α-Fe as a result of the effects of dissolved hydrogen. We find that hydrogen charged specimens after plastic deformation display a very characteristic pattern of trailing dipoles and prismatic loops which are absent in uncharged pure metal We explain these observations by use of a new self consistent kinetic Monte Carlo model, which was initially used to predict the observed microstructure. The results of this combined theory and experimental study is to shed light on the fundamental mechanism of hydrogen enhanced localised plasticity. The energy per unit length of dislocation is prescribed in the following line tension expression[9],
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