Prediction of enthalpy of formation and Gibbs energy change in pseudo-binary (Ti–Zr)(Fe–Cr)<Subscript>2</Subscript> and pseudo-ternary (Ti–Zr)(Fe–Cr)<Subscript>2</Subscript>-H system using extended Miedema model

The thermodynamic model proposed by Miedema is capable of predicting the enthalpy of formation (ΔH) and relative stability of phases in binary but not in ternary or multi-component systems. While developing nanocrystalline binary/ternary metal hydrides for compressor-driven reversible heating–cooling applications, it is necessary to identify appropriate alloy compositions with suitable hydrogen storage capacity and reversible hydrogen absorption–desorption capability. Accordingly, a suitable modification of the Miedema model is proposed in the present study for calculating ΔH of AB₂ type of pseudo-binary (Ti–Zr)(Fe–Cr)₂ and pseudo-ternary (Ti–Zr)(Fe–Cr)₂-H alloys. Subsequently, Gibbs energy (ΔG) of the possible phases is estimated to predict relative phase stability/equilibrium in a given system. It is shown that grain size or interfacial energy contribution exerts a significant influence on ΔG and relative stability of the phases beyond a critical value/limit. Finally, the predicted phase equilibrium from this model-based calculation is validated by suitable comparison with relevant experimental data reported in the literature.     

Analytic evaluation of hydrogen-assisted void growth at high temperatures

We propose a model of grain-boundary growth of voids caused by diffusion in the presence of hydrogen. The influence of hydrogen is simulated by taking into account its pressure in the cavities. To evaluate the pressure of hydrogen, we perform the thermodynamic analysis of two-phase metal-cavity systems. Unlike traditional approaches, the newly proposed equation takes into account changes in the surface energy depending on the concentration of hydrogen and gives much more moderate estimates for the intermal pressure of hydrogen. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 4, pp. 75–86, July–August, 1997     

Photolytic properties of a pulsed discharge in water

Results are presented of an experimental investigation of the photolytic properties of a pulsed discharge in water. A model is proposed for this process which satisfactorily describes the dependence of the hydrogen peroxide concentration on the specific discharge energy. Pis’ma Zh. Tekh. Fiz. 24, 91–95 (February 12, 1998)     

Effect of residual stress-strain profiles on hydrogen-induced fracture of prestressing steel wires

We analyze the influence of the distributions of residual stresses and strains formed after the surface treatment of cold-drawn steel wires used as the reinforcement of prestressed reinforced concrete on the susceptibility of these wires to hydrogen embrittlement characterized by the time to fracture in the tests carried out according to the regulations of the FIP (Fédération Internationale de la Précontrainte). A computational model is proposed for the prediction of the durability of wires in corrosive hydrogenated media. In the model, the accumulation of hydrogen in potential sites of fracture as a result of diffusion under the influence of stresses and plastic strains is analyzed and a criterion of critical concentration of hydrogen specifying the time of local fracture depending on the stress-strain state is formulated. The enables us to predict the influence of specific features of the distributions of residual stresses and plastic strains after various types of thermal treatment on the durability of wires under the conditions of hydrogen embrittlement. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 2, pp. 105–112, March–April, 2006.     

Reduction of aluminum oxide in a nonequilibrium hydrogen plasma

A new method is proposed and experimental investigations are carried out aimed at reducing aluminum oxide in a nonequilibrium hydrogen plasma of a combined glow discharge (CGD) at a pressure of 1315.8–13,158 Pa, a discharge current of 5·10⁻²–3 A, and a hydrogen flow rate of 10⁻⁶–10⁻⁴ nm³/sec. A high degree of conversion of the aluminum oxide (60%) with an energy consumption of 20 kW·h/kg of Al₂O₃ is attained. Reduction of metals from oxides and other compounds in a CGD nonequilibrium hydrogen plasma can be used for producing rare-earth and high-purity metals. Translated from Inzhenerno-Fizcheskii Zhurnal, Vol. 73, No. 3, pp. 580–584, May–June, 2000.     

Experimental and analytic evaluation of the influence of high-pressure hydrogen on the low-cycle fatigue of steels

We have established correlations between the effect of hydrogen under a pressure of 35 MPa on the low-cycle fatigue of 15 corrosion-resistant steels, on the one hand, and their initial mechanical characteristics and the parameter of austenite stability A _γ on the other. Materials with A _γ<1 are subjected to catastrophic degradation in hydrogen. We have proposed relations that enable one to range adequately steels with different structures according to their hydrogen resistance and to regulate this property of steels by means of alloying. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 5, pp. 110–112, September–October, 2007.     

Spectroscopic investigation of the thermal stability of bound hydrogen in a-C: H

Equilibrium between free and bound hydrogen in amorphous hydrogenated carbon has been investigated by infrared spectroscopy. A quasireversible departure of hydrogen from the bound state is observed. The activation energy of the bound-quasifree hydrogen chemical reaction and the rate of return of hydrogen to the bound state are estimated. An energy diagram is proposed for the bound-quasifree hydrogen reaction. Pis’ma Zh. Tekh. Fiz. 23, 1–7 (April 12, 1997)     

A Thermodynamic Property Model for the Binary Mixture of Methane and Hydrogen Sulfide

A thermodynamic property model with new mixing rules using the Helmholtz free energy is presented for the binary mixture of methane and hydrogen sulfide based on experimental P_ρ T_x data, vapor–liquid equilibrium data, and critical-point properties. The binary mixture of methane and hydrogen sulfide shows vapor–liquid–liquid equilibria and a divergence of the critical curve. The model represents the existing experimental data accurately and describes the complicated behavior of the phase equilibria and the critical curve. The uncertainty in density calculations is estimated to be 2%. The uncertainty in vapor–liquid equilibrium calculations is 0.02 mole fraction in the liquid phase and 0.03 mole fraction in the vapor phase. The model also represents the critical points with an uncertainty of 2% in temperature and 3% in pressure. Graphical and statistical comparisons between experimental data and the available thermodynamic models are discussed     

Temperature dependences of the mechanical properties of austenitic and martensitic steels in hydrogen

The influence of gaseous and preliminarily dissolved hydrogen on the characteristics of short-term static strength, crack resistance, and low-cycle durability of martensitic and austenitic steels is studied within the temperatures range 293–1073°K, under pressures of hydrogen varying within the range 0–35 MPa, for the strain rates of 0.01–100 mm/min, and the strain amplitudes of 0.8–1.6%. We determine the loading rates and the conditions of action of hydrogen leading the maximum possible hydrogen degradation of each material. The influence of the chemical composition and structural state on the degree of embrittlement and fractographic features of the fracture of steels in the presence of hydrogen is analyzed. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 5, pp. 53–64, September–October, 2007.     

Corrosion and electrochemical properties of binary cobalt and nickel alloys

The influence of pH of electrolyte on the tungsten content and current efficiency of a Co–W coating is determined. We determine the corrosion rates of Co–W and Ni–Pd alloys by the polarization resistance method and show that the coatings are classified as belonging to highly corrosion-resistant coatings. The catalytic reactivity of coatings in a model reaction of hydrogen release is assessed. Dependences of the corrosion resistance and catalytic reactivity of Co–W and Ni–Pd alloys on the contents of the components are obtained, and their character is justified. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 6, pp. 89–92, November–December, 2008.     

Accelerated method for hydrogen degradation of structural steel

We develop a new accelerated method for aging structural materials in gaseous hydrogen. It is based on the acceleration of diffusion processes (responsible for the structural degradation of the metal) under the influence of hydrogen and can be described as thermal cycling of materials in hydrogen. The range of thermal cycling is chosen according to the data on the operating conditions of steam pipelines of thermal power plants. The structural changes detected in the metal after laboratory aging for 40h are similar to those observed after 140,000–190,000h of operation. For the quantitative estimation of the level of degradation of the metal, we use the parameters of growth of a fatigue crack. It is experimentally shown that the effective threshold fatigue characteristics can be useful for the analysis of the current state of the metal and the proposed method of aging can be used for the determination of its residual service life. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 34, No. 4, pp. 45–52, July–August, 1998.     

Relaxation methods for the investigation of the influence of surfactants on the rate of corrosion

We develop a theory of the application of low-level relaxation methods (basic and pulse potentiostatic methods, basic and pulse galvanostatic methods, and the method of electrode impedance) to the investigation of the influence of surfactants on the rate of corrosion. To evaluate the possibilities of this theory. we consider an example of a corrosion model characterized by the adsorption of surfactants which affects the rates of both cathodic and anodic processes. The cathodic process includes the adsorption of hydrogen atoms and the anodic process includes the adsorption of subions of the metal. We deduce equations for the calculation of the electrode parameters of the model on the basis of the experimental data and show that the complexity of the proposed model is maximum for all relaxation methods, except the method of electrode impedance. Dneprodzerzhinsk State Technical University, Dneprodzerzhinsk. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 32, No. 4, pp. 75–80, July–August, 1996.     

A method for the prevention of premature failures of power plants using hydrogen as the working medium

Qe analyze failures of power-generating units working on liquid hydrogen caused by the most dangerous type of embrittlement—reversible hydrogen embrittlement of the metal. We consider the existing methods for the protection of various structural elements against hydrogen embrittlement and discuss their advantages and shortcomings. A method for the protection of difficultly accessible internal hollows of power-generating units against hydrogen embrittlement by introducing active gaseous admixtures in the working volume is described in detail. The mechanism of action of these admixtures is analyzed refractory alloy as examples, we demonstrate the positive effect of admixtures to gaseous hydrogen under a pressure of 35 MPa. The proposed method enables one, in some cases, to use hydrogen (as a new ecologically pure fuel) without serious changes in the structure of the unit and in the technological process. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 34, No. 4, pp. 53–56, July–August, 1998     

Cold cracks in welded joints of structural steels

The present survey is devoted to the investigation of a dangerous phenomenon (quite often observed in the process of arc welding) of the formation of hydrogen-induced cold cracks in welded joints of structural steels. We briefly analyze the existing models of the mechanism of hydrogen embrittlement. It is shown that difficulties in understanding the processes of initiation and growth of cold cracks are explained not only by the necessity of determination of the principal factors which govern the embrittling action of hydrogen but also by the absence of reliable knowledge of the microscopic mechanisms of fracture processes in metals. We suggest a new model of hydrogen embrittlement of metals with bcc lattice developed at the Paton Institute of Electric Welding. According to this model, atomic hydrogen adsorbed on the metal surface in the form of anions affects the surface energy of submicrocracks appearing in dislocation clusters in the process of deformation whose initial period of propagation obeys the classical Griffith scheme. The proposed model enables one to explain all known distinctive features of the cold cracking of welded joints and forms a groundwork for the physical simulation based the use of mathematical methods and aimed at the quantitative evaluation of the contribution of each factor to the indicated processes. Paton Institute of Electric Welding, Ukrainian Academy of Sciences, Kiev. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 32, No. 1, pp. 53–66, January–February, 1996.     

Decarbonization mechanisms of polycarbosilane during pyrolysis in hydrogen for preparation of silicon carbide fibers

Polycarbosilane (PCS) fibers are cured by electron beam irradiation in helium. Then, the cured fibers are pyrolyzed under hydrogen. The mechanisms of carbon removal during pyrolysis are investigated using chemical elemental analysis, FTIR, Raman, and AES analysis. The development of microstructure and phase is examined by SEM, TEM, and XRD. The results show that the thermal cleavage of relatively weak Si–H and Si–CH₃ bonds takes place first during pyrolysis in hydrogen, generating free radicals. The free radicals then react with C–H bonds or with each other to form Si–CH₂–Si groups, releasing hydrogen and methane. As temperature increases, the Si–CH₂–CH₂–Si groups in PCS begin to dissociate and react with hydrogen to form methane, resulting in the further removal of carbon and giving silicon-rich silicon carbide fibers (i.e. C/Si <1).     

Destructive effect of hydrogen on the strength of materials in nonstationary temperature fields

We develop a calculational model of the growth of internal cracks caused by the supersaturation of materials with hydrogen released from the solid solution into internal cavities of the metals. The pressure of hydrogen depends on the rate of changes in temperature, local dissolution of hydrogen in the inhomogeneities, diffusion coefficients, and crack sizes. We estimate the residual service life of the vessel of a reactor for hydrocracking of petroleum. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, Lviv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 32, No. 4, pp. 31–35, July–August, 1996.     

Distinctive features of hydrogen degradation of heat-resistant alloys based on nickel

We present the comparative data on the resistance to hydrogen degradation of three oodifications of dispersion-hardened heat-resistant KhN60MV alloy (in deformed, as-cast, and powder forms) under the conditions static tension in gaseous hydrogen under a pressure of 35 MPa in the temperature range 293–1093°K. We show that the powder modification is preferable under pressure of 0–35 MPa in the temperature range 293–1093°K. It exhibits a high level of strength, the lowest sensitivity to hydrogen degradation, and the maximum stability of plastic properties. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 4, pp. 115–120, July–August, 1997.     

A method for determination of the diffusion coefficient of hydrogen in titanium alloys by chemical etching

We propose a model of absorption of hydrogen by titanium alloys in the process of chemical etching. We obtained a solution that describes the amount of absorbed hydrogen and its distribution in the metal as a function of the rate and time of etching. On the basis of the equations obtained, we developed a method for determination of the diffusion coefficient of hydrogen in a metal. The essence of the method is a sequential etching of a specimen in hydrogenated and nonhydrogenated solutions and determination of the amount of hydrogen which remains in the metal. The effective diffusion coefficients of hydrogen in titanium alloys with various structures are found. Central Institute of Aircraft Motor Building, Moscow, Russia. Tupolev Aircraft Scientific and Technical Association, Moscow, Russia. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 34, No. 4, pp. 107–112, July–August, 1998.     

Analysis of the creep and long-term strength of VT6 titanium alloy with preliminarily injected hydrogen

We describe the results of experimental and theoretical investigation of the influence of the concentration of preliminarily injected hydrogen on the creep and long-term strength of VT6 titanium alloy under the action of tensile stresses equal to 47–217 MPa. The tests carried out at a temperature of 600°C show that hydrogen (up to 0.3 wt.%) strongly decreases the steady-state creep rate of this alloy, increases the time to fracture, and lowers (severalfold) its ultimate fracture strain. The obtained results are interpreted on the basis of the analysis of changes in the structural state of the alloy. The proposed version of the kinetic theory of creep gives good agreement between the experimental and theoretical values of the principal characteristics of creep and long-term strength. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 5, pp. 98–104, September–October, 2008.