New Protective Coatings for Replacing Cadmium Coatings on Steel Parts

Works aimed at solving the problem of replacing toxic cadmium coatings used for protection of aircraft steel parts are reviewed. Numerous electrolytic alloys based on zinc and zinc-bearing coatings of the Colsil and Dacromet types are suggested for the purpose. A VIAM-designed coating based on a Zn – Sn alloy in combination with a modified phosphate coating is considered. It is shown that the protective properties of the combined coating are close to those of a cadmium coating, and the former is recommended for commercial use.     

Kinetics and mechanism of low-pressure,high-temperature oxidation of silicon-II

The reaction of oxygen at low pressures with silicon layers on tungsten ribbons was studied. An abrupt transition was observed between a condition of passivation, in which a thin film of SiO₂ formed at low temperatures, and a steady-state combustion condition at high temperatures. The latter state is characterized by the formation of volatile SiO. The boundary between these two states has been defined in terms of the pressure-temperature relation. Oxygen consumption in the combustion state is represented by first-order reaction kinetics with an activation energy of 13 ± 1 kcal/mole. The stability of the two states has been defined by a thermodynamic analysis of the SiO₂ layer stability. The oxygen consumption dependence on temperature has been described by a kinetic model which involves a consideration of the various elementary steps in the reaction.     

Influence of alloying elements on the structure and wear resistance of chilled cast iron

To work out the optimal chemical composition of wear-resistant cast iron with a pearlitic metallic matrix that is able to restore the relief of a rough surface, we investigated the properties of cast iron with different composition by the method of single factor experiment.Nizhnii Novgorod Branch of the Central Research Institute of Structural Materials Prometei. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 37–39, June, 1994.     

Peculiarities of the Effect of Perchlorate Ions on Electrodeposition of Cadmium in Aqueous–Acetonitrile Electrolytes

It is shown that, depending on the composition of aqueous–acetonitrile solvent, either acetonitrile (AN) molecules or perchlorate anions predominantly adsorb on the electrode. The highest surface concentration of AN and the lowest rate of cadmium electroreduction are observed in the mixture with the most loosened structure (x ₂ 0.4). The salting-out action of mixed solvent in the domains of its structure stabilization primarily manifests itself in an increase in the adsorption activity of ClO^– ₄ anions and a corresponding promotion of Cd²⁺ discharge as a result of " effect. The maximum process rate is observed in the domain, where the AN structure is ordered by monomeric water molecules.     

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.     

Water-Acetonitrile Ratio in Perchlorate Cadmium Bath and the Effectiveness of the Addition of Crown-Ester

It is shown that the strongest deceleration of the electrodeposition of cadmium in inhibited media is observed in the domain of loosening the structure of a mixed solvent (0.45 x ₂ 0.25) when the molecular adsorption of organic solvent on Cd is maximum. The process is maximally facilitated in the domain of ordering the acetonitrile's (AN) structure (0.9 x ₂ 0.75), where perchlorate anions dominate at the cathode surface. Crown-ester exhibits maximum inhibition effect under the conditions of preferential adsorption of its molecules, i.e., in the domain of the prevalence of the nonaqueous component in the mixture (x ₂ 0.95).     

The “overheating” phase in YuNDKT alloys

Conclusions In alloys of the YuNDKT type the chemical composition of the overheating phase is the same as that of phase. The phase impoverished in iron and enriched in titanium is not overheating phase but a region of the matrix bordering this phase.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 72–74, March, 1973.     

High-resolution SIMS and analytical TEM evaluation of alumina scales onβ-NiAl containing Zr or Y

High-resolution SIMS and TEM have been used to evaluate growth processes and interfacial segregation occurring in -Al₂O₃ scales grown at 1200°C on -NiAl containing zirconium or yttrium.¹⁸O/SIMS shows that the extent of aluminum diffusion occurring during -Al₂O₃ growth is reduced by the presence of these alloying elements, which are seen by SIMS imaging as oxide particles within the scale. STEM/EDS of the same oxide scales show that zirconium and yttrium also segregated to the oxide-alloy interface to the extent, respectively, of 0.15 and 0.07 of a monolayer and to oxide grain boundaries (0.2 monolayer). The complementary information provided by SIMS, TEM, and STEM provides a better understanding of the role of reactive elements in modifying scale-growth processes.     

Structural parameters of structural steel determining its resistance to hydrosulfuric cracking

Conclusions To attain high resistance to hydrosulfuric cracking of steels for drive pipes, it is necessary after heat treatment to attain a structure with the following parameters: size of the coagulated carbide (M₃C) particles d0.05 m to eliminate the possibility of nascent hydrogen accumulating on the carbide-matrix interfaces; subgrain size d>0.30 m to ensure relief of internal stresses, and dislocation density p<-10⁹ cm^–2 to eliminate places of possible localization of hydrogen.I. P. Bardin Central Research Institute of Ferrous Metallurgy. Siberian Branch of the Special Design Bureau of the Scientific and Production Association Soyuzgazavtomatika, Saratov. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 11, pp. 19–20, November, 1991.     

Austenitic stainless steels strengthened by phase strain hardening and aging

Conclusions Nonmagnetic stainless steels of the Kh12N12T3 and Kh12N14T3 type have good mechanical properties after phase strain hardening and aging (_0.2 = 685 - 785 MPa, _b = 1275 MPa, 20%) as compared with the properties of Fe-Ni-Ti austenitic steels with 26–30% Ni. After phase strain hardening and aging the stability of these steels is high with respect to the transformation during cold treatment.IFM UNTs AN SSSR. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 57–60, June, 1981.     

Oxide particles in Ag-Mg alloys formed by internal oxidation

Gravimetric measurements at low temperatures (<600°C) and for dilute Ag-Mg alloys have given further information about the mechanism of oxide formation. This investigation shows that the fixation rate of oxygen is very high, which assumes the existence of species in an oxidized form, including one or two magnesium atoms called elementary species and denoted as MgO^* and Mg₂O^*. When there are no free magnesium atoms, there is a coalescence process with the fixation of oxygen atoms or MgO^* and Mg₂O^*: this process leads to the formation of the first clusters including an oxygen excess. At low temperatures, the thermal fluctuations do not permit significant changes. There is no significant increase in cluster size, but a rearrangement of these clusters toward a compact structure with the release of excess oxygen. Their size is less than 1 nm.     

Structure and Mechanical Properties of Maraging and Low-Carbon Martensitic Steels

The structure, mechanical properties, and crack resistance after tempering of maraging steel 03Kh11N10M2T (EP-678) and low-carbon martensitic steel 12Kh2G2NMFT are studied. The range of tempering temperatures ensuring the combination of properties required for massive parts (_r #x2265; 1300 MPa, _0.2 1100 MPa, KCT 0.2 MJ/m²) is determined. It is shown that steel 12Kh2G2NMFT is better adaptable to manufacture because it is hardened by air-cooling.__________Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 32 – 35, January, 2005.     

Sulfur segregation during the high-temperature oxidation of chromium

A TEM and STEM examination has been carried out of cross-sectioned specimens of convoluted chromia scale formed by oxidizing chromium at 950° C. Sulfur was detected at the oxide/metal interface and the oxide grain boundaries (apart from low-angle grain boundaries), but not within the oxide grains. These results are consistent with the sulfur effect theory.     

Degradation of zirconium-containing nickel-based alloys in a hydrogen-hydrogen sulfide environment

The modes of degradation experienced by a Ni-15Cr and three Ni-15Cr-xZr alloys (where x=1, 5, or 10 wt. %) after exposure to a 1% H₂S/H₂ gas mixture at 1000° C have been examined, with particular reference to the morphological features. The addition of Zr at about the 1% level has been shown to have a beneficial effect, in terms of reduced weight gain relative to the Ni-15Cr control, explained by a thinner more protective external CrS scale, and a decreased tendency for CrS subscale formation (internal sulfidation). Zr additions beyond 1%, up to 5 and 10%, become increasingly detrimental principally on account of extensive internal ZrH_x formation, associated with the selective attack of the increasing amounts ofNi₅Zr in the alloy microstructures. The mode of action of Zr at about the 1% level in these alloys is considered in the light of earlier studies concerning the performance of similar alloys in O/S atmospheres.     

Strain-Activated Hydrogen Absorption during Heat Treatment of Al–Zn–Mg–Cu Alloy AA7475

Subsurface porosity due to hydrogen absorption (commonly known as high-temperature oxidation, or HTO) in an Al–5.5% Zn–2.25% Mg–1.5% Cu alloy during heat treatment in undried air at 515°C is accentuated by prior strain. Under the uncontrolled atmospheric conditions used, the critical strain level for the onset of HTO is about 1.5%; increasing strain results in more porosity and surface blistering. If NaBF₄ is added to the furnace atmosphere, no porosity is evident at strain levels up to 5%.     

Oxidation Behavior of Two-Phase γ + σ Nb-Ti-Al Alloys

The oxidation behavior of a series of single-and two-phase Nb-Ti-Al alloys, selected from the sameextended + tie-line, was investigated at1200°C in air. The single-phase alloy suffered from extensive internal oxidation andoxidized at a much higher rate than the single-phase alloy. In a two-phase + microstructure, the phase was preferentiallyattacked to form internal alumina andTi-rich nitride. This preferential attack of limited the extent to which the phase wasinternally oxidized, but also interrupted the formationof a continuous alumina scale. The single-phase alloyalso did not form a continuous alumina scale. Theinability of the phase to form continuousalumina was attributed to a combination of nitrideformation and internal oxidation. The oxidation behaviorof the two-phase + Nb-Ti-Al alloys isdiscussed in terms of mechanisms developed for theoxidation of binary, two-phase alloys.     

A correlation between the Pilling-Bedworth ratio and the radius of curvature of metallic substrates with coherent thin oxide layers

A correlation between the radius of curvature of metallic substrates with strainfree coherent monolayers of oxides and the Pilling-Bedworth ratio was found to follow the expression ¦R¦19.5/¦–1¦ for a large number of metal- oxide systems in which the metal and the oxide have identical cubic structures. For any given Pilling-Bedworth ratio , the radius of curvature of basally oriented hexagonal substrates was lower than that when the surface was perpendicular to the basal plane.     

Kinetics of Cadmium Electrodeposition in Perchlorate Water-Ethanol Electrolytes

It is found that promotion of electrode process of Cd deposition is caused by the formation of unstable solvates of discharging ions with adsorbed alcohol molecules (zone of water structure stabilization) or by the effect manifestation as a result of preferential adsorption of perchlorate anions (zone of alcohol structure stabilization). The minimum rate of cadmium ion electroreduction is observed in the mixtures with the maximum loosening of structure under the conditions of preferential adsorption of nonaqueous solvent molecules and is associated with the blockage of cathode surface and the variation in potential under the adsorption of cation complexes with organic ligands.     

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.     

Interdiffusion Behavior of Ni–Cr–Al–Y Coatings Deposited by Arc-Ion Plating

Ni–Cr–Al–Y coatings were deposited on the Ni3Al–base superalloys IC-6 and K17 by arc-ion plating. The results indicated that a small amount of substrate atoms, such as Co, Ti, Mo, etc., existed in the Ni–Cr–Al–Y coatings near the substrates, probably due to sputter and antisputter. For the alloy K17, the impeding effect of Al was not obvious, because the temperatures of the substrate and the coating were high (420–480°C) during the deposition process and interdiffusion was accelerated. However, for alloy IC-6 which contains Al, as well as a high concentration of Mo, the diffusion of Cr was impeded. Vacuum heat treatment at 1050°C drastically increased diffusivities and the presence of Al and Mo was not enough to prevent some Cr diffusion. Thus, the coating became more uniform and close to the desired composition.