Structure-Selective Dissolution of Al–Fe–Ni Bronze in Chloride Electrolyte

The selectivity of the anodic dissolution of the iron-rich phases of . 9-4-4-1 cast bronze in 0.5 N NaCl + 0.01 N HCl was studied. X-ray diffraction analysis revealed that the Fe₃Al and ₁-phases present at the surface of the initial bronze become predominantly etched during the early period of anodic dissolution at E = –0.12 V (NHE). According to electrochemical and analytical data, the above phases dissolve at this potential most rapidly. The x-ray diffraction data agree well with the results obtained by atomic absorption analysis of the solution.     

General laws governing variation in properties of cast alloys of the Al-Zn-Mg system

Among existing high-strength corrosion-resistant aluminum alloys, those of the Al-Mn-Zn system are most promising. They have a different phase composition, depending on the content of magnesium and Zinc: + (Al₃Mg₂), + + T(Al₂Mg₃Zn₃), + T, + T + (MgZn2) and + The majority of industrial Al-Mg-Zn alloys correspond to the phase regions + T and + T + with respect to composition. A high level of strength and satisfactory overall corrosion resistance are characteristic for these alloys. Al-Mg-Zn alloys may, however, tend to the most dangerous form of corrosion - stress-induced corrosion cracking. Using methods of experiment planning in the study, we investigated Al-Zn-Mg alloys of various compositions for the purpose of selecting alloy compositions with a high level of mechanical properties and stress-induced corrosion cracking.All-Union Scientific-Research Institute of Aviation Materials. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 12, pp. 24–28, December, 1994.     

Resistance of 1201 aluminum alloy to plastic deformation at various strain rates

Conclusion With an increase in the rate of plastic strain there is a change in the resistance of 1201 alloy to plastic deformation, which is revealed in a nontraditional decrease in _0.2 and increase in , and A_p. The characteristics _k and _t increase nonlinearally.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 56–61, August, 1989.     

Two-phase ferritic-martensitic steels

Conclusions The results of laboratory and production experiments showed that the main condition for providing the necessary combination of properties of two-phase ferritic-martensitic steels (high tensile strength, low yield strength, high plasticity and work hardenability) is obtaining the specified quantity of the hardening phase (martensite) in the structure (20–28% M to obtain _t 550 MPa or 10–18% M for _t 450 MPa). The specified ratio of the structural constituents under conditions of mass production of two-phase ferritic-martensitic steels may be guaranteed only with the use of steels containing carbon and alloy elements within the necessary limits and also with strict observance of the heat-treatment cycle. Without the use of metallographic measurements as the criteria for obtaining the optimum structural condition in addition to the required values of strength and plasticity it is necessary to use the _0.2/_t ratio, which must not be greater than 0.5–0.6 with the absence of yield points on the tensile curve (without special temper rolling).As the result of the combination of work done in the Central Scientific-Research Institute of Ferrous Metallurgy together with plants of the Ministries of Ferrous Metallurgy and of the Automobile Industry at present the production is being introduced and experimental production lots of heat-treated two-phase steels of the following types with guaranteed mechanical properties are being supplied:At the Novolipetsk Metallurgical Combine cold-rolled 0.7–2.0-mm sheet of 06KhG(S)Yu and 06G2SYu steels with _0.2 = 260–320 MPa, _t 550 MPa, ₄ 30%, and _0.2/_t 0.5–0.6.At the Cherepovets Metallurgical Combine hot-rolled 2–6-mm sheet of 09G2(S) steel with _0.2 = 260–320 MPa, _t 550 MPa, ₄ 25%, and _0.2/_t 0.5–0.6.At the Beloretsk Metallurgical Combine (billets melted and rolled at the Cherepovets Metallurgical Combine) heat-treated cold-drawn wire up to 10.5 mm in diameter of 06KhGR steel with _0.2 250 MPa, _t 530 MPa, and ₁₀ 30%.For successful development of the production and use of two-phase ferritic-martensitic steels the combined work of the designers of machine building plants on determination of the most effective types of parts, of engineers on correction of the method taking into consideration the specifics of the properties of two-phase ferritic-martensitic steels, and of users on determining the service properties of parts of these steels is necessary. The fulfillment of such a combination of work will make possible th timely formulation of the further work of the metallurgical industry and determination of the required volume and product range of rolled products of two-phase ferritic-martensitic steels.I. P. Bardin Central Scientific-Research Institute of Ferrous Metallurgy. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 11, pp. 25–29, November, 1984.     

The Corrosion of Alloy Steels under Antirust Compounds in the Presence of Microbes

The kinetic corrosion characteristics of 352-, 302, and 30 steels with rust-preventive compounds applied are investigated in an industrial neutral electrolyte, depending on whether a compound is infected with microorganisms or not. The effect of microorganisms and their metabolites on the corrosion of steels greased with the compounds are assessed.     

Role of Adsorbed Metal Complexes in Cadmium Electrodeposition from Iodide-Containing Aqueous Ethanol

Structurization phenomena in a mixed solvent were found to determine, by affecting the solvation degree of an anion, its adsorptivity at the electrode and, consequently, the surface concentration of the nonaqueous solvent. The formation of activated Cd²⁺ complexes with iodide anions in an adsorbed layer is usually accompanied by accelerating the electrode reaction. The desalting effect of the mixed solvent in the zones of its structural stabilization is mainly manifested as the enhanced adsorptivity of iodide anions and the correspondingly facilitated discharge of metal ions. The highest discharge rate was found at ₂ 0.9 when the structure of EtOH is ordered with monomeric water molecules. The highest surface concentration of EtOH and the lowest rate of cadmium electroreduction correspond to a structurally disordered mixture ( ₂ 0.4).     

Influence of original structure and heating rate on the properties of steel after hardening from the intercritical range

Conclusions The original condition and heating rate determine the mechanical properties of the steel after hardening from the intercritical range. The best properties, particularly ductility, _t=1600 MPa, _0.2=1250 MPa, =14%, anda _n=0.9 MJ/m², are obtained after preliminary hardening from 930°C, tempering at 200°C, a second hardening from 800°C (5% ferrite), and tempering at 200°C. Full hardening from 930°C with subsequent tempering at 200°C (without preliminary hardening) makes it possible to obtain _t=1550 MPa, _0.2=1200 MPa, =9%, anda _n=0.9 MJ/m².Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 52–56, May, 1981.     

Influence of the Anion Nature and the Metal-to-Additive Ratio on the Effectiveness of ε-Caprolactam during Cadmium Electrodeposition

The rate and mechanism of cadmium(II) electroreduction from electrolytes containing -caprolactam were found to significantly depend on the metal-to-additive ratio. Whatever the anion nature, the process sharply accelerates in the presence of an excess of cadmium cations, which form activated surface complexes with adsorbed -caprolactam molecules as bridging ligands. With an excess of the additive, metal depolarization due to the "-effect still persists in perchlorate media; in iodide solutions, -caprolactam inhibits this process. The formation of a dense adsorbed film composed of -caprolactam molecules and I^– anions at the electrode ensures a high throwing power of the electrolyte and makes it possible to obtain uniform elastic organocadmium plating.     

Analytical study of surface and bulk oxidation of Astroloy

Nickel-base alloys, such as Astroloy, used for aeronautical turbine disks, are sensitive to time-dependent cracking in environments containing oxygen. The mosaic structure of the alloy consisting islands (200 nm average size) surrounded by the -phase (100 nm thick) induces complex oxidation phenomena. Various analytical approaches allow the delineation of all the steps from segregation to oxidation occurring on the surface of such a duplex structure. The protection of Astroloy by its outer oxide layer against oxygen penetration was studied also, using alternative ¹⁶O₂ then ¹⁸O₂ oxidation. In association with STEM studies, it is shown that the outer oxide scale is not a real barrier against oxygen penetration and that inner precipitation of chronium (+ aluminium and titanium)-enriched oxides, takes place especially in the structure.     

Effect of the tempering temperature and time on the structure and phase composition of the AMg6 alloy

Conclusions It was determined that the decomposition of the solid solution in the AMg6 alloy begins at the grain boundaries. After a certain time interval the plate-like -phase precipitates within the grains. After a longer tempering time the platelets coagulate and take on a rounded form.At temperatures of 200 and 250°C the metastable -phase is not completely converted into the -phase, and even after a very long tempering time there is still a considerable amount of the -phase in the structure.At a temperature of 150°C or lower, only the metastable -phase occurs in the alloy even after tempering as long as 9 months.Translated from Metallovedenie i Termichesakaya Obrabotka Metallov, No. 9, pp. 59–61, September, 1966.     

Formation of a Rhenium-Base Coating on a Nb-Base Alloy

To protect Nb–5Mo–15W alloy against high-temperature oxidation a novel coating was developed involving electroplating of a Re–Ni film, followed by pack cementation with Cr and Al. The coating consisted of a duplex-layer structure, an inner (Re–Cr) or Re(Cr) layer and an outer Cr(Al) or NiAl layer. The Re–Ni film containing more than 70at.%Re, developed in the present investigation, is more useful than the conventional low Re–Ni film. The inner (Re–Cr) and Re(Cr) layer acts as a diffusion barrier between the Nb–5Mo–15W alloy substrate and the outer -Cr(Al) or -NiAl layer, which forms a protective -Al₂O₃ scale. The coated Nb–5Mo–15W alloy was oxidized in air at 1373K for up to 360ks, showing very good oxidation resistance.     

On the Removal of Aluminide Coating from Blades of Gas Turbin Engine

The peculiarities of removing -11 coating from 32 type alloy in an acidic etching bath depending on the concentration and ratio between the amounts of potassium bichromate and ammonium heptamolybdate additives are studied with gravimetrical and electrochemical methods. The results are explained by the peculiarities of bichromate and molybdate ions adsorption at the surface and their oxidizing properties. Baths providing sufficiently quick removal of the coating at a minimum alloy surface etching are recommended.     

Phase relations in the Fe-Ni-Cr-S system and the sulfidation of an austenitic stainless steel

The stability fields of various sulfide phases that form on Fe-Cr, Fe-Ni, Ni-Cr, and Fe-Cr-Ni alloys have been developed as a function of temperature and the partial pressure of sulfur. The calculated stability fields in the ternary A-B-S system are displayed on plots of log vs. the conjugate extensive variable (n_A/n_A–n_B), which provides a better framework for following the sulfidation of Fe-Cr-Ni alloys at high temperatures. Experimental and estimated thermodynamic data were used in developing the sulfur potential diagrams. Current models and correlations were employed to estimate the unknown thermodynamic behavior of solid solutions of sulfides and to supplement the incomplete phase-diagram data of geophysical literature. These constructed stability field diagrams are in excellent agreement with the sulfide phases and compositions determined experimentally during the sulfidation of SAE 310 stainless steel. The sulfur potential plots appear to be very useful in predicting and correlating the sulfidation of commercial alloys.Nomenclature a _i Activity of componenti - G ⁰ Standard Gibb's free energy change - G ^M Integral molar free energy of mixing - G _i ⁰ Partial molar free energy of mixing of componenti - H Standard enthalpy change - H _i Partial molar enthalpy (heat) of mixing of componenti - H ^M Integral molar enthalpy (heat) of mixing - K Equilibrium constant - n _i Moles of componenti - p _{s 2} Partial pressure of diatomic sulfur - R Gas constant - S _i Partial molar entropy of mixing of componenti - S ^M Integral molar entropy of mixing - S ⁰ Standard entropy change - T orK Absolute temperature - X _i Mole fraction of componenti - _i Activity coefficient of componenti - _i Relative chemical potential of componenti     

SiO(g) formation from SiC in mixed oxidizing-reducing gases

The formation of SiO(g) from SiC by either active oxidation or an oxidation-reduction process is discussed. The Wagner criterion for the transition from active to passive oxidation is generalized for any oxidant. Kinetic modeling of both active oxidation and oxidation-reduction is described.Symbols - - MW _SiC/MW _Si - _CO CO(g) boundary layer thickness - _ox gaseous-oxidant, boundary layer thickness - stoichiometric factor from Eqs. (2)–(4), # of CO produced/# of oxidant (on oxygen atom basis) - gas viscosity - concentration of diffusing gas species in boundary layer - concentration of major gas species in boundary layer - _oxide density of SiO₂ - D diffusion coefficient of diffusing species in gas-boundary layer - D _CO diffusion coefficient of CO(g) - D _ox gas diffusion coefficient of oxidant - J flux, rate of weight loss limited by diffusion in gas-boundary layer - J _CO flux of CO(g) - J _ox flux of gaseous oxidant - K _g linear oxide growth constant, weight/(length² time) - k _g linear oxide growth constant, length/time - k _l linear volatilization constant for SiO₂,k _lo+k _ls, weight/(length² time) - k _lo linear volatilization constant for oxygen from SiO₂, weight/(length² time) - k _ls linear volatilization constant for silicon from SiO₂, weight/(length² time) - k _l linear volatilization constant for SiO₂, length/time - k _p parabolic oxide growth constant, weight²/(length⁴ time) - k _p parabolic oxide growth constant, length²/time - L sample length parallel to gas flow direction - (M/A)₁ specific weight change due to oxygen gain and associated carbon loss in paralinear oxidation - (M/A)_1L limiting value of weight change due to oxygen gain and associated carbon loss in paralinear oxidation - (M/A)₂ specific weight change due to silicon loss and associated carbon loss in paralinear oxidation - MW _C molecular weight of carbon - molecular weight of O₂ - MW _Si molecular weight of silicon - MW _SiC molecular weight of silicon carbide - molecular weight of silica - n number of oxygen atoms per oxidant molecule - P _CO ^eq eqiilibrium CO(g) pressure - P _CO ^g CO(g) pressure outside of boundary layer - P _CO ⁱ CO(g) pressure at SiC-gas interface - P _ox ^g oxidant gas pressure outside of boundary layer - P _ox ⁱ oxidant gas pressure at SiC-gas interface - R gas constant - t time - T absolute temperature - v linear gas velocity - x oxide thickness - x _L limiting oxide thickness achieved in paralinear oxidation - x _t oxide thickness at which transition from linear to parabolic growth occurs     

Effect of lamellar structure parameters on the properties of titanium alloy VT3-1

Conclusion An increase in the ultimate breaking strength, stress-rupture strength, and fatigue limit of alloy VT3-1 with a lamellar structure may be achieved as a result of refining any parameter of the structure, particularly -phase platelet thickness, and increasing the volume fraction of secondary -phase. An increase in ductility characteristics, toughness, and creep resistance may be provided by increasing the dimensions of -colonies and primary -phase particles (up to 2.5–3.5 m) and reducing the volume fraction and dispersivity of secondary -phase lamellar precipitates. Coarsening of -grains leads to an increase in a_c, k_Q, and refinement leads to an increase in and a_n.Qualitative dependences for mechanical properties of alloy VT3-1 on lamellar structure parameters made it possible to isolate those structural parameters which have the most marked effect on properties.The properties of alloys with a finely lamellar structure (d25 m, b_{I, II}<2 m) are most sensitive to structure. In this case a change in -colony size by 10 m and -platelet thickness by 1 m affects the properties 3–20 times more strongly than a change in -grain size by 100 m. The effect of finely dispersed secondary -phase precipitates is greater, the coarser the primary -phase structure. Refinement of primary -phase structure with an increase in secondary phase platelet thickness to 1 m or more reduces the sensitivity of alloy mechanical properties to the effect of secondary -phase.With coarsening of the intragranular structure (d>25 m, b_{I, II}2 m) the effect of structural parameters d and b on properties is markedly weakened: on strength properties (_f, ₁₀₀ ⁴⁵⁰ ) by a factor of 100, on ductility (, ), by a factor of 10 to 20, and on impact strength and fracture toughness (a_n, a_c, K_Q) by a factor of five.The qualitative relationships obtained between structure and mechanical properties of alloy VT3-1 are fundamental for controlling the structure of semifinished titanium alloy products.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 52–55, July, 1986.     

Oxidation properties of Fe-5Cr-4Al (wt.%) alloys in oxygen at temperatures 1000°C–1320°C

Oxidation kinetics of a parent Fe-5Cr-4Al alloy subjected to two types of anneals were investigated at temperatures ranging from 1000°C to 1320°C. The alloy annealed at 850°C exhibited a rapid transient oxidation stage associated with growth of nodules containing iron oxides and internal precipitation of -Al₂O₃ in the alloy beneath these nodules. The nodules nucleated and grew from sites located in the regions of the alloy grain boundaries during the period of rapid alloy grain growth. Nodular growth virtually ceased when a continuous -Al₂O₃ film formed at the nodule-alloy interface. The alloy subjected to anneal at 1000°C and at the reaction temperature to stabilize the alloy grain size tended upon oxidation to form a protective -Al₂O₃, layer by parabolic kinetics at temperatures to 1250°C. If this alloy was oxidized in stages at 1000°C, a protective -Al₂O₃ scale was formed up to 1320°C. The temperature coefficient of the parabolic oxidation kinetics was consistent with diffusion processes at boundaries of the -Al₂O₃ grains playing an essential role during growth of this protective oxide layer.     

On the oxidation ofα-Fe andε-Fe2N1−z : I. Oxidation kinetics and microstructural evolution of the oxide and nitride layers

The oxidation of -Fe and -Fe₂N_1–z at 573 K and 673 K in O₂ at 1 atm was investigated by thermogravimetrical analysis, X-ray diffraction, light-optical microscopy, scanning electron microscopy and electron probe X-ray microanalysis. Upon oxidation at 573 K and 673 K, on -Fe initially -Fe₂O₃ develops, whereas on -Fe₂N_1–z initially Fe₃O₄ develops. In an early stage of oxidation the oxidation rate of -Fe₂N_1–z appears to be much larger than of -Fe. This can be attributed largely to an effective surface area available for oxygen uptake, which is much larger for -Fe₂N_1–z than for -Fe due to the porous structure of -Fe₂N_1–z as prepared by gaseous nitriding of iron. The development of a magnetite layer in-between the hematite layer and the -Fe substrate, at a later stage of oxidation, enhances layer-growth kinetics. After 100 min oxidation at 673 K the (parabolic) oxidation rates for -Fe and -Fe₂N_1–z become about equal, indicating that on both substrates the oxide growth is controlled by the same rate limiting step which is attributed to short-circuit diffusion of iron cations. Oxidizing -Fe₂N_1–z increases the nitrogen concentration in the remaining -iron nitride, because the outward flux of iron cations, necessary for oxide growth, leads to an accumulation of nitrogen atoms left behind.     

Thermoelastic transformation in Cu - Al - Mn alloys

Heat treatment of Cu - 10%Al - Mn alloys with a low concentration of manganese can be accompanied by a transformation. The effect of manganese on the temperature range of this transformation and its kinetics is investigated.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 5 – 6, August, 1996.     

Oxygen-18 tracer study of the passive thermal oxidation of silicon

This work focuses on the thermal oxidation of silicon near 1273 K using the double-tracer oxidation method. The results confirm that oxidation occurs by the transport of electrically neutral non-network oxygen through the interstitial space of the vitreous silica (-SiO₂) scale. Simultaneously, self- (or isotopic-) diffusion occurs in the network, resulting in characteristic isotopic fraction distributions near the gas-scale interface. The self-diffusion coefficients calculated from these profiles agree with those reported for tracer diffusion in -SiO₂, and the diffusion coefficient calculated from the scale growth is consistent with reported O₂ permeation data. An important parameter that describes the double-oxidation behavior is the ratio of the value of /(D _nt),where is the scale thickness grown during the second oxidation, D_n is the network self-diffusion coefficient for oxygen, and t is the time of the second oxidation.     

Thermal Resistance of Low-Alloyed Chromium Alloys

The oxidation kinetics of low-alloyed -2 and 1-17 chromium alloys is investigated at a temperature from 1273 to 1673 K for 1000 h. It is shown that even at a temperature from 1473 to 1673 K the heat resistance of these alloys is higher than that of the 648 nickel-containing alloy at a temperature from 1273 to 1373 K. This allows to recommend the alloys as heat-resistant materials operating at a temperature up to 1573 K.