Solid State Phenomena Vol. 225

Abstract: The problem under consideration concerns the prevention of absorption of hydrogen in the processes of corrosion and electroplating of all industrially used metals with the aim of the modification of chemical and physical properties of base metal surface. Its properties change towards better brightness and soldering, minimal porosity and hydrophilicity of surface, increase of hardness and wear resistance. All these properties were evaluated by means of appropriate test equipment. Residual stresses in Cr coating by phase transformation, beginning in the electroplating process, acted in combination with absorbed huge quantity of hydrogen in intrinsic defects in the steel base. Internal stresses in the base/coating region resulted in severe deterioration of the durability of steel parts, as identified by static or sign-variable fatigue tests. The new stress-step technique makes possible an analysis of H content as a function of the depth in base metals and its distribution in coating metal .

Abstract: The experimental data on efficiencies of a series of 7 ureides and 5 acetylides as inhibitors (IN) of corrosion of mild steel in Postgate B media compared to quantum chemical data; the following descriptors found to be essential to describe the inhibitive properties under given conditions: energies of the boundary molecular orbitals (HOMO and LUMO) and dipole moment. The inhibitive properties of the chosen ureides under given conditions are based on electron donating rather than accepting properties of their molecules. PM/3 method was found to be preferable compared to other quantum chemical methods used (i.e., MNDO, AM/1), and even non-empiric ab initio methods because it is found to be more helpful in explaining the mechanism of inhibitive action of organic species.

Abstract: The present paper offers a continuum modelling of trap-affected hydrogen diffusion in metals and alloys, accounting for different physical variables of both macroscopic nature (i.e., related to continuum mechanics, e.g., stress and strain) and microscopic characteristics (material microstructure, traps, etc.). To this end, the model of hydrogen diffusion assisted by the gradients of both hydrostatic stress and cumulative plastic strain, stress-and-strain assisted hydrogen diffusion, proposed and frequently used by the authors of the present paper (Toribio & Kharin) is analysed in addition to other well-known models such as those proposed by (i) McNabb & Foster, (ii) Oriani, (iii) Leblond & Dubois, (iv) Sofronis & McMeeking, (v) Krom and Bakker, showing their physical and mathematical differences and similarities to account for different physical variables.

Abstract: A results of test of erosion and corrosion resistance of pearlitic gray cast iron (grade EN GJ 400) are showed. The NaCl solutions and of ethylene glycol solutions were used as the test environment. Examination were performed at varying cavitation load, in the range 2,8 ÷ 20 W/cm².

Abstract: Results of an analysis of effect of wearing type on surface structural changes of a Ni₃Al intermetallic alloy, are shown in the present paper. A microstructure evaluation was carried out by Quanta 3D FEG field emission gun scanning electron microscope (FEG SEM) equipped with an integrated EDS/WDS/EBSD system. The Ni₃Al-based intermetallic alloy with an addition of boron, zirconium and chromium was examined. The investigated material had γ’ single-phase, ordered solid solution structure with 20 μm grain size. An electron backscatter diffraction (EBSD) method was applied to visualize surface structural changes upon an abrasive, a cavitational and a tribological wearing of the material.An observation of surface layer after the abrasive wear was carried out on samples examined in loose abradant by T-07 tester and according to GOST 23.2008-79 norm. An analysis of cavitational wear on changes in the near surface area of Ni₃Al-based alloy was performed on an impact-jet stand. Observed structural changes were described based on results of the SEM/EBSD complex structural examination and hardness measurements. It was found, that the EBSD is an effective and sensitive method that allows estimating surface strain introduced during analyzed wearing types.

Abstract: Hydrogen diffusion within a metal or alloy is conditioned by the stress-strain state therein. For that reason it is feasible to consider that hydrogen diffuses in the material obeying a Fick type diffusion law including an additional term to account for the effect of the stress state represented by the hydrostatic stress. In this paper the hydrogen transport by diffusion in metals is modelled in notched specimens where loading generates a triaxiality stress state. To this end, two different approaches of stress-assisted hydrogen diffusion, one-dimensional (1D) and two-dimensional (2D), were compared in the vicinity of the notch tip in four notched specimens with diverse triaxiality level at two different loading rates. The obtained results show that the 2D approach predicts lower values of hydrogen concentration than the 1D approach, so that a loss of directionality of hydrogen diffusion, depending on both notch geometry parameters (radius and depth) and loading rate, appears when a 2D approach is considered.

Abstract: It is experimentally established that air-tested samples of degraded material showed tooth flow that disappears for tests in hydrogen. The main feature inherent in the studied materials are metastable and presence of more or less pronounced time-and temperature-dependent processes of structural relaxation, which reduces the total free energy of a thermodynamic system. The values of fracture toughness minimize the square deviation of experimentally obtained values drift from the theoretical curve corresponding to the exponential relaxation function.

Abstract: The bending fatigue strength of 17CrNi6-6 steel subjected to vacuum carburizing with high pressure gas hardening has been measured using a novel high-frequency technique. The test records the changes in resonance and consists of observing resonance frequency changes in a vibrating system with a single degree of freedom as a result of the forming of a fatigue crack. Moreover, a mechanism of fatigue nucleation and propagation in steel hardened by vacuum carburizing is presented.

Abstract: It is experimentally established that illumination of GaSe (Pb) hydrogen saturated layered semiconductor electrodes in acids (H₂SeO₃, H₂SO₄) and neutral (water) environments has improved the anode and cathode reactions.The influence of H₂SeO₃ solution on the potential of open circuit and current density is different for crystals in initial state and after hydrogenation. During the sunlight irradiation, polarization takes place at the low values of current density and more positive value of potentials in comparison with the result obtained in darkness. Taking into account the results, obtained also in the acid H₂SO₄ environments, we have established that anode and cathode reactions have a slower character and run at the more negative potential values in comparison with the neutral environment.