HYDROGEN GROUP
The group studies the state of hydrogen atoms in Fe- and Ni-based solid solutions and their interaction with crystal lattice imperfections, hydrogen-induced phase transformations, mechanisms of plastic deformation and fracture. The main goal is to clarify physical mechanisms of hydrogen embrittlement (HE) and search for hydrogen-resistant alloys.
Main scientific results:
(i) Using Mössbauer spectroscopy and electron spin resonance, an effect of hydrogen on interatomic bonds in iron-based alloys is studied and it is obtained that hydrogen increases the concentration of free electrons like it occurs for nitrogen in the fcc iron.
(ii) A nature of hydrogen-induced phases is studied using the low temperature X-ray and neutron diffraction, and it is shown that the only hydrogen-caused phase transformation is the partial fcc®hcp transition. It is shown that the fcc so-called g* phase does not really exist and the hydrogenated fcc austenite is just an inhomogeneous solid solution.
(iii) The pseudo-hydride hypothesis of HE of austenitic steels is tested using X-ray studies and mechanical tests, and it is shown that the hydrogen-induced hcp martensite reveals no harmful effect on plasticity of hydrogenated steels.
(iv) Using internal friction technique, the hydrogen-caused early start of the dislocation sources and increased velocity of dislocations are demonstrated. An effect of alloying elements on the migration enthalpy of hydrogen atoms in the solid solution is measured and its correlation with the hydrogen-caused degradation of plasticity is found.
(v) Hydrogen-caused relaxation phenomena in nickel are studied using internal friction technique and a mechanism of hydrogen Snoek-Köster relaxation is proposed.
(vi) A new approach to the mechanism of hydrogen embrittlement is proposed based on the local increase of the concentration of free electrons by the hydrogen atom clouds at dislocations, which leads to a decrease in the stacking fault energy and localisation of plastic deformation in the slip planes, decrease in the line tension of dislocations and distance between them in pileups, and, as a result, to the early start of microplastic deformation, enhanced mobility of dislocations, early opening of microcracks, their fusion on the slip planes and macroscopic pseudo-brittle fracture.
