Isothermal formation of the ε-phase after phase hardening in ferromanganese alloys

Conclusions The investigations carried out show that isothermal formation of the -phase can be controlled not only by alloying, but also by means of repeated phase transitions. Reduction of the temperature at which the formation of the -phase commences intensifies the isothermal transformation near the martensite point and at room temperature. The latter is valid if the -transformation during continuous cooling begins not lower than the temperature at which the isothermal soaking is carried out, otherwise the intensity of the isothermal process decreases, and the lower the commencement of the -transformation with respect to the temperature isothermal line, the more the intensity drops. It was found that if the -phase forms at –60, –70°C, there is a complex dependence between the rate of the isothermal process and the temperature.It was demonstrated that when the -transformation temperature is fairly low, austenite can be supercooled by rapid cooling and the -phase may form during heating. Given the same supercooling rate, the transformation of austenite into -phase during heating is more complete when the heating rate is slow.It was noticed that if in continuous cooling the -phase forms at –60, –70°C, preliminary supercooling broadens the temperature range over which the isothermal -transformation is observed. The intensity of the process is influenced by the heating rate after supercooling.It was found that the maximum amount of -phase forming in the alloy G19 during continuous cooling after repeated phase transitions and subsequent isothermal soaking does not exceed 50–55%.It was discovered that isothermal soaking at room temperature in between repeated phase transitions intensifies the stabilization of the austenite.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 2–8, April, 1965     

Control of the phase composition and nitrogen content in the nitride layer in the nitriding of the steel 38Kh2MYuA

It is known that in order to obtain a high-hardness, wear- and corrosion-resistant article a nitrided layer of nitride (+)-phases should be formed on its surface. However, in some cases, for example, in nitriding high-speed die steels and steel 38Kh2MYuA, the formation of brittle nitride surface layers should be eliminated and only a zone of internal nitriding (a+ + MN) should be formed in order to provide the requisite hardness and wear resistance. The article concerns preparation of nitrided layers with different compositions on the widely used 38Kh2MYuA nitralloy.     

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.     

The Effect of the ε-Caprolactam Concentration on the Electrodeposition of Nickel–Polymer Coatings

It is shown that an increase in -caprolactam concentration in sulfate nickel-plating baths enhances its adsorption on Ni cathode, which is followed by the formation of its complexes with nickel ions in the solution. The first process decelerates the electrode reaction, and the second one facilitates it. In the interval of the maximum deceleration of the process, nickel–polymer coatings with the greatest content of -caprolactam and the highest surface conductivity, substantially exceeding that of pure metal, are formed.     

Metastable manganese austenite as a structural base of high-stability steels conditions of dynamic contact loading

Important regular features of the structure and special features of the behavior of metastable manganese austenite under conditions of quasistatic deformation and dynamic contact loading are considered. Based on the correlation of the energy of packing defects of manganese austenite with the kinetics of deformation martensitic transformations { , } and the capacity for deformation strengthening and relaxation of stresses, principles for choosing the base composition of metastable austenitic steels with a high operating stability for different conditions of dynamic contact loading are established.     

Influence of deformation and annealing on the structure of continuously cast BrOTsS5-5-5 bronze

Conclusion Continuously cast billets of BrOTsS5-5-5 bronze have quite high internal stresses occurring as the result of formation of the casting, which are added to the deformation stresses, and lead first to the formation of a twinned structure (with =30%) and then to failure of the material (with =40%). In comparison with permanent mold ones the structure of such billets is coarse grained with strictly oriented axes of the dendrites in the direction of the solidification front.All-Union Scientific-Research and Design Institute for Secondary Nonferrous Metallurgy. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 59–60, August, 1984.     

Plating Kinetics and Quality of Copper-Organic Coatings

During the cathodic deposition of copper from sulfate electrolytes containing -caprolactam, the process inhibition is shown to be caused by adsorption of electroactive complexes formed in the surface layer via an interaction between the metal ions and adsorbed additive molecules. A correlation between the metal nature and the catalytic or inhibiting effect of -caprolactam, which can polymerize at the electrode due to electric current, is revealed. It is found that composition and properties of copper-organic coatings can be controlled by varying the -caprolactam concentration.     

Effect of alloying element content on ion-nitriding behavior of Fe-Ti alloys

The ion-nitriding behavior of iron alloys with a titanium content of between 1.07 and 2.58 wt.% was investigated in the -phase region. The behavior was found to be analogous to the internal oxidation behavior of iron alloys: An internal-nitriding layer, where small TiN precipitates are dispersed, as well as a very thin surface layer of -Fe₄N were formed. A parabolic rate law holds for growth of the internal-nitriding layer. The kinetics of growth of the internalnitriding layer is discussed according to the rate equation of internal-oxidation, giving the diffusion coefficient of nitrogen, D _N ^app , in the layer. The measured D _N ^app decreases as the volume fraction of TiN, f, increases, indicating that the diffusion of nitrogen is apparently inhibited by the existence of TiN precipitates. Furthermore, the diffusion coefficient of nitrogen in -iron was evaluated by extrapolating D _N ^app to f=0, being in good agreement with that reported previously. The f-dependence of D _N ^app is discussed in terms of the effective area for diffusion of nitrogen in -iron.     

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.     

On the oxidation ofα-Fe andε-Fe2 N1−z II. Residual strains and blisters in the oxide layer

The development of residual strains in the iron-oxide layers growing on -Fe and -Fe₂N_1–z at 673 K in O₂ at 1 atm was investigated by X-ray diffraction at room temperature. After correction for thermal-strain development due to cooling after oxidation, it was found that tensile growth strains occur in magnetite and compressive growth strains occur in hematite. The growth strains in the oxides on -Fe are (in absolute sense) 2–3 times as large as those in the oxides on -Fe₂N_1–z. Buckling of the oxide layer occurs in the case of an -Fe substrate, which is attributed mainly to relaxation of the growth strains in magnetite and hematite. Thermal-strain development during cooling enhances the tendency for buckling. Buckling is not observed for oxide layers on -Fe₂N_1–z, which could be due to the smaller values of absolute strain in the oxide layer on -nitride. The absolute values of the growth strains in the oxide layer on -nitride being smaller is attributed to microstructural changes in the nitride layer during oxidation.     

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.     

Effect of Deformation and Heat Treatment on the Structure and Properties of Quenched and Aged Alloy 36NTYu

Variation of the structure and mechanical properties of alloy 36NTYu after various kinds of treatment (quenching with aging at 750°C, deformation with degree = 50 – 98%, annealing at 750°C) studied by mechanical tensile and fatigue tests is described. The changes in the dislocation structure and lamellar segregations of -phase in the treatment process are determined. It is shown that the fatigue limit and the friction stress are well correlated.     

"Microduplex" structure in industrial aging alloys

Conclusion Finely disperse biphase structure (microduplex) forms in the process of high-temperature recrystallization of strongly deformed alloys containing particles of -phase in the deformed lattice.Novosibirsk Institute of Railroad Transport Engineers. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, p. 40, June, 1984.     

Application of Electrochemical Impedance Method to Studying Corrosion of Porous Powder Steels

Electrochemical impedance spectroscopy (10⁴–10^–3 Hz) and weighing methods are applied to studying the corrosion behavior of powder austenitic 316L stainless steel with a porosity = 15, 20, and 38% and compact steel of the same composition in a 3% HCl + 5% NaCl solution and oil pool water (pH 6.0; total mineralization 184.8 g/l, preferentially chlorides of Na, Ca, and Mg). Hodographs and phase angles of the electrode impedance are analyzed for high ac frequencies. The procedure of corrosion rate determination for powder steel from impedance data is described. The corrosion rate of powder steel calculated to the geometric surface area of a sample is shown to increase in acid and neutral chloride solutions with an increase in the porosity of samples from 15 to 38%, and, at 20%, with the exposure of samples to the electrolytes (from 2 to 120 h). Advantages of the impedance method over the weighing method are demonstrated for determination of the corrosion rate of porous powder steels. Based on impedance measurements, the specific surface areas of powder steel samples are assessed.     

Electroplating of Copperorganic Coatings from Perchlorate and Chloride Baths Containing ε-Caprolactam

The mechanisms of reactions, which occur both in solution and at the electrode during copper plating from perchlorate and chloride baths in the presence of -caprolactam capable of electrochemical polymerization are studied. It is shown that the formation of complexes by additive molecules with metal ions in the bulk of solution enhances its inhibiting effect and improves the quality of Cu-organic coatings. Complex formation also favors the increase in the adsorption of anions at the electrode. By varying the concentration of -caprolactam, it is possible to control the deposition rate and the composition and properties of the coatings.     

Electrochemical Behavior of Nickel Hydride in Sodium Hydroxide Solutions

Electrochemical behavior of nickel hydride Ni₂H (-phase) is studied in 0.01–1 N NaOH by using common (VA) and cyclic (CVA) voltammetry, chronocoulometry, amperometry, and potentiometry. The limiting anodic and cathodic currents in VA and CVA curves are caused by the hydride decomposition via the following scheme Ni₂H -phase Ni + H_abs, where the intermediate -phase contains 0.003 at. % H, that is, one tenth that in the saturated -phase (0.03 at. %). At open circuit, the hydride maintains the equilibrium hydrogen potential. In the first 30 min, the hydrogen ionization from hydride is limited by solid-state diffusion and, later, the hydride decomposition. The anodic process involves ionization of sorbed hydrogen, while the cathodic process represents its electrochemical desorption: H₂O + H_ads + e H₂ + OH^–. The hysteresis observed in the cathodic CVA and open-circuit chronograms of the hydride potential in the beginning of anodic dissolution reflect the changes in the surface coverage of hydride with adsorbed hydrogen. The rate constant of hydride decomposition k, the rate Vitself, and the equilibrium constant K are as follows: k = k = 8 × 10^–5 s^–3, V = 3 × 10^–5 C/cm², and K = 10. The kinetic parameters of hydrogen electrochemical ionization from the hydride are b _a = 0.12 V and = 0.5.     

Composition Dependence of the Kinetics and Mechanisms of Thermal Oxidation of Titanium-Tantalum Alloys

The oxidation behavior of titanium-tantalumalloys was investigated with respective concentrationsof each element ranging from 0 to 100 wt.%. Alloys wereexposed to argon-20% oxygen at 800 to 1400°C. Theslowest oxidation rates were observed in alloys with5-20% Ta. The oxidation kinetics of alloys containingless than approximately 40% Ta were approximatelyparabolic. Pure Ta exhibited nearly linear kinetics. Alloys containing 50% or more Taexhibited paralinear kinetics. The activation energiesfor oxidation ranged between 232 kJ/mole for pure Ti and119 kJ/mole for pure Ta, with the activation energies of the alloys falling between these values andgenerally decreasing with increasing Ta content. Theactivation energies for oxidation of the end members, Tiand Ta, agree well with published values for the activation energies for diffusion of oxygenin -Ti and Ta. Scale formation in the alloys wasfound to be complex exhibiting various layers of Ti-,Ta-, and TiTa-oxides. The outermost layer of the oxidized alloys was predominately rutile(TiO₂). Beneath the TiO₂ grew avariety of other oxides with the Ta content generallyincreasing with proximity to the metal-oxide interface.It was found that the most oxidation-resistant alloys hadcompositions falling between Ti₅Ta andTi-15Ta. Although Ta stabilizes the -phase of Ti,the kinetics of oxidation appeared to be rate limited byoxygen transport through the oxygen-stabilized -phase.However, the kinetics are complicated by the formationof a complex oxide, which cracks periodically. Tantalumappears to increase the compositional range ofoxygen-stabilized -phase and reduces both the solubilityof oxygen and diffusivity of Ti in the - and-phases.     

The reaction of nitrogen with titanium between 800 and 1200°C

This paper describes phase formation and mass transport during the reaction of iodine-refined titanium with nitrogen at 760 Torr and 800 to 1200°C. Each titanium-nitrogen phase is present within the composition and temperature range of its thermodynamic stability. Between 882 and 1110°C there are the nitrides, TiN and Ti₂N, and solutions of nitrogen in and -titanium. There is no -titanium below 882°C or Ti₂N above 1110°C. The growth of each phase layer involves some favorably oriented grains from among the many that are nucleated. Nitrogen concentration gradients exist in all phases. Nitrogen is the predominant diffusing species in all phases but a small amount of outward diffusion of titanium occurs through the nitrides, producing -phase porosity above 1100°C. There is some porosity in the outer regions of TiN. All phases remain mechanically sound and coherent with each other. Changes in the relative proportions of phases during cooling are identified, which enables corrections to be made to kinetic data for the reaction.     

The improved wear resistance of gray cast irong after low-temperature liquid cyaniding

Conclusions The increase in the wear resistance of gray cast irong after low-temperature cyaniding in molten urea and soda is due to the saturation of the surface with nitrogen and carbon. A substantial increase in the wear resistance is obtained for cast iron containing aluminum, which results in the formation of nonbrittle phase and high microhardness of the base metal in the zone saturated with nitrogen below the carbonitride layer.All-Union Scientific-Research Institute of Textile and Light Machine Construction. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 52–53, January, 1972.