Effect of phase transitions in Fe-Cr-Al alloys on their corrosion resistance in gases and liquid metals

We investigate the process of oxidation of Fe-Cr-Al alloys in argon and liquid sodium at a temperature of 650°C for 1000 h, analyze distinctive features of the process of formation of surface oxide and sub-oxide layers, and demonstrate the effect of phase transitions in alloys on the corrosion losses in these media. The process of oxidation of ferrochrome alloys in the region of homogeneity of -solid solutions in both media results in the formation of oxide layers based on Al₂O₃ on the surface of aluminum-containing alloys. In an atmosphere of argon, the intense growth of the oxide layer promotes the formation of residual stresses followed by its destruction and exfoliation, which leads to an increase in corrosion losses. In liquid sodium, aluminum improves the corrosion resistance of ferrochrome alloys, which is explained both by the suppression of formation of unstable compounds (sodium chromites and ferrates) and the appearance of an interlayer of -phase inclusions between the Al₂O₃ film and the matrix. This interlayer inhibits the growth of the protective oxide layer and enhances its adhesion to the matrix. The -phase is formed in homogeneous ferrochrome -alloys as a result of saturation of their surface layers with carbon present in sodium. If the composition of Fe-Cr alloys is close to equiatomic, their corrosion resistance catastrophically decreases as a result of the bulk transformation which is typical of both media.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 31, No. 6, pp. 59–66, November – December, 1995.     

Transfer of copper and zinc in polymeric materials oxidized in contact with brass

Transfer particularities were investigated for zinc and copper in polymeric films oxidized in contact with brass. Inversion in selectivity of alloy component transfer proved to be the fact for a wide range of polymers. The results obtained are explained by an irregular development of oxidative transformations within the polymer layer, thus leading to a two-stage mode of transfer in the case of catalytically active metals. The influence of various factors (e.g., oxidation temperature, polymer film thickness, polymer origin) on the level of ultimate concentrations of copper and zinc accumulated in polymers was considered. © 1995 John Wiley & Sons, Inc.     

Study of the outlook for the development of the gas industry in Russia and analysis of risk associated with this process

The gas industry in Russia will develop under conditions of the persistence of existing risks and emergence of the new ones caused by the world financial crisis, increased uncertainty in estimating world prices for natural gas, together with disturbed balance between interests of gas producers and consumers, and threat of loss of the competitiveness of Russian natural gas on foreign markets. In this context, in choosing a strategy of the development of the gas industry and its production-and-financial program, it is necessary to carry out a risk analysis of optimum decisions. Specific features of carrying out a risk analysis and results of the risk analysis of strategic decisions that would provide enhanced steadiness and the effectiveness of the development of the gas industry under conditions of the uncertainty of both external and internal factors are presented.     

Formation of intermetallic layers on the surface of refractory metals in a lead melt under conditions of mass transfer

We investigate the kinetics of the interaction between refractory metals (Mo, Nb, and V) and Kh18N10T steel under the conditions of concentration mass transfer by a lead melt at a temperature of 1000°C. In the experiment, the sealed ampul made of austenitic steel is a source of nickel, iron, and chromium. Refractory metals are practically insoluble in lead. Among the components of steel, nickel is transported first (due to the highest solubility) and forms a continuous nickel layer on the surface of refractory metals (Me). In the course of time, the mass transfer of nickel stops owing to a decrease in its concentration in the surface layers of steel, while iron and chromium are transported further and deposit on the nickel substrate. The conditions of dissolution of the components and the formation of intermetallic compounds in the case of interdiffusion of the components on the Me−Ni and Fe(Cr)−Ni interfaces are considered. It is shown that, at the initial stage of the interaction, the nickel interlayer facilitates the interdiffusion of a refractory metal and the transported components (Fe, Cr). The intermetallic layer forms gradually in a rather wide concentration range, which is associated with stress relaxation. It adheres well to the matrix and is free of cracks, flakes, and other damages, caused by abrupt volume changes on the formation of intermetallic compounds. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 2, pp. 92–97, March–April, 1999.     

Corrosion of 20Kh13 steel in lead melts saturated with oxygen

We study the high-temperature interaction (650°C, 500 h) of 20Kh13 chromium steel with melts of stagnant lead saturated with oxygen (C _{O [Pb]} ≈ 6 · 10⁻³ wt.%). First (up to 200 h), separate islands of Me₃O₄ oxides (Me: Fe, Cr, Pb) are formed on the steel surface. In the course of time (for 500 h), these islands completely cover the steel surface as a result of lateral growth. The upper part of the oxide layer is formed by the (Fe_{1 − x} Pb_x) O · Fe₂ O₃ complex oxide growing from the initial “solid-metal—melt” interface toward the liquid-metal medium. The inner part of the oxide layer is spinel [(Fe_{1 − x} Pb_x) O · (Fe_{1 − y} Cr_y)₂O₃] enriched with chromium and formed on the basis of the matrix. Both layers symmetrically grow with respect to the initial “solid-metal—melt” interface. Lead does not penetrate into the steel matrix and is fixed only in the oxide layer. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 5, pp. 36–40, September–October, 2005.