Effect of the method of production of an Ni<Subscript>3</Subscript>Al/Mo layered composite material on its structure and properties

A stack of alternating 25 100-μ-thick Ni₃Al plates and 28 200-μm-thick Mo plates is subjected to hot isostatic pressing (HIP) at a temperature T = 1200°C and a pressure P = 150 MPa for τ = 2.5 h followed by hot rolling at 1050–950°C to a thickness of 2.3 mm. The stack is then subjected to cold rolling (CR) to a thickness of 0.5 mm without intermediate annealing, subsequent annealing during HIP at T = 1200°C, P = 150 MPa, and τ = 2.5 h, and CR to a thickness of 0.22 mm. Upon CR at a strain ε changing from 80.8 to 95.8%, the following specific structure forms in the longitudinal direction: molybdenum layers acquire a wavelike structure, can contact with each other, form “cells,” and retain almost the same thickness, and Ni₃Al alloy layers are rejected between the molybdenum layers to form a regular structure made of alternating thickenings and thinnings across the rolling direction. Annealing during HIP and subsequent CR to ε = 98.2% lead to the formation of zones with a broken alternation of layers in the longitudinal and transverse directions, which is related to different strain resistances of the (more refractory) molybdenum and Ni₃Al layers at 20°C. The adhesion between the layers is good, and no intermediate phases form at the interface. The ultimate bending strength of the 2.3-mm-thick workpiece at 20°C is 1000 ± 100 MPa, and the prepared material has a plasticity margin.     

Thermodynamic properties of liquid alloys of the Ni-Hf system

By the method of calorimetry in isoperibolic conditions are determined integral and partial mixing enthalpies of liquid alloys of the Ni-Hf system at 1770 ± 5 K. Defined that liquid Ni-Hf alloys are formed with allocated large quantity of heat. The analysis of own and literary data has allowed to establish for mixing enthalpies of binary Ni-Hf liquid alloys dependence on temperature. With use of the Schröder equation are calculated the activities of studied alloys components from co-ordinates of liquidus line of the phase diagram of this system. Between calculated and experimentally established values of melts components activities of the Ni-Hf system is observed only qualitative consent. Are also calculated ΔG and ΔS of liquid Ni-Hf alloys.     

Structure and hot hardness of RuAl-based alloys produced by reactive sintering using hot isostatic pressing

The structure and hot hardness (at temperatures up to 1100°C) of RuAl-based powder alloys with 1–3 at % Ni, Mo, Re, or Ru are studied. The alloys are produced by the reactive sintering of cold-compacted bars and subsequent threefold isostatic pressing with intermediate annealing at 1500°C performed after the first hot isostatic pressing. The samples have a residual pore content of 1–2.5 vol % and are characterized by a micrononuniform distribution of base and alloying elements. The alloys with refractory metals, such as Re, Mo, or Ru, are found to have the maximum hardness at all temperatures under study. At low temperatures, the effect is more substantial; the hardness of the Re-containing alloys exceeds that of the other alloys by a factor of 1.3–3.6. The increase in the hardness related to solid-solution alloying becomes more substantial owing to the microinhomogeneity of the sintered powder alloys and weakens because of microporosity. Recommendations that allow the uniformity of the distribution of the base and alloying elements to be increased are given.     

Deposition from the two-phase multicomponent flow of a vacuum-arc plasma containing droplets of an evaporated material

The interaction of a surface with the two-phase flow of a multicomponent vacuum-arc plasma containing droplets of an evaporated material along with multicharged ions and neutral atoms is studied. For the two-phase flow of a multicomponent plasma, the dependences of the ion-current density, the deposition rate, and the heat flow to a substrate on the bias voltage are obtained, and the conditions at which the coating deposition rate is inverted are determined. A unique probe technique for the plasma flow generated by an end-face Hall plasma accelerator with a “cold” eroded cathode is used to determine the volt-equivalent energy U** of the interaction of the two-phase plasma flows of Ti, Al, Cr, and an Ni-Cr-Al-Y alloy with a surface and the self-sputtering coefficient of the Ni-Cr-Al-Y alloy and its elements (Ni, Cr, Al) as a function of the bias voltage. Metallographic analysis is used to study the structure of thick (～100-μm) coatings deposited from the two-phase flow of a metallic multicomponent vacuum-arc plasma.     

Formation of the limiting nanostructural state in metals during plastic deformation

The mechanisms that determine the formation kinetics of the limiting states in deformed solid nanostructures are considered. These states are characterized by the minimum average nanocrystallite size. The limiting states are shown to correspond to the point of dynamic equilibrium between the deformation-induced competing processes of nanograin fragmentation and growth.     

Effect of alloying and irradiation on the behavior of interstitial impurities in vanadium and V-Ga and V-Ti-Cr alloys

The effect of alloying and fast-neutron irradiation on the behavior of interstitial impurities in vanadium and V-Ga and V-Ti-Cr alloys is studied using low-frequency internal friction. It is found that, before irradiation, oxygen and nitrogen impurities in plain vanadium and V-Ga alloys are in a solid solution, whereas, in V-Ti and V-Ti-Cr alloys, they are predominantly fixed to form chemical compounds. Unlike the irradiation of plain vanadium, the irradiation of V-Ga alloys at 673 K to a neutron fluence of 4.24 × 10²⁵ m^?2 (E > 0.1 MeV) does not knock out oxygen and nitrogen impurities from interstitial positions in the lattice to the positions of radiation defects. In the V-5Ti-5Cr alloy, oxygen and nitrogen atoms are fixed before and after neutron irradiation according to these conditions.     

Rare-earth metals (REMs) in nickel aluminide-based alloys: II. Effect of a REM on the phase composition of a multicomponent Ni<Subscript>3</Subscript>Al-based alloy

The hardening mechanisms are studied in the cast high-temperature next-generation materials that are based on the intermetallic compound Ni₃Al and are low alloyed with refractory (W, Re, Mo, Cr) and reaction- and surface-active (REM, Ti, etc.) metals. The interaction of the main impurities (C, O, Si, S) with three characteristic representatives of the REM group (namely, Y, La, Ce), which can be used for alloying, is analyzed. The reported data on the behavior of some REMs in the alloys based on nickel monoaluminide NiAl are considered. The effect of the REMs on the phase compositions of real multicomponent semicommercial Ni₃Al-based VKNA alloys produced by directional solidification is investigated, and the excess phases precipitating upon alloying are revealed. Alloying with refractory metals and REMs is shown to lead to the formation of nanophases that stabilize the dendritic or single-crystal structure of VKNA-type cast alloys and strengthen the interface boundaries in them.     

Corrosion resistance of vanadium alloys clad by a ferritic corrosion-resistant steel in liquid-metal heat-transfer agents

The results of studying the corrosion resistances of steels of various classes and vanadium-based alloys in liquid-metal heat-transfer agents (lithium, sodium, lead) are analyzed. These structural materials are shown to have satisfactory corrosion resistance in high-purity liquid metals. However, a nitrogen impurity in lithium and an oxygen impurity in sodium and lead cause the degradation of the mechanical properties and the fracture of the vanadium alloys. The use of these alloys clad by a ferritic corrosion-resistant steel is shown to ensure high corrosion resistance of the fuel-element can materials in fast neutron reactors with sodium and lead heat-transfer agents.     

Paraequilibria in the Fe-Si-C system and their relation to the bainite transformation in steels

The thermodynamic properties of silicon-containing cementite and ε carbide are estimated, and the results obtained are used to perform the thermodynamic calculation of paraequilibria in the Fe-Si-C system. Even a relatively low silicon content is shown to substantially change the positions of virtually all boundaries of phase fields in the Fe-C phase diagram. The relation between the paraequilibria and bainite transformation was analyzed. The maximum supersaturation of retained austenite is found to be controlled by a thermodynamic factor, namely, the solubility of the paraequilibrium cementite. The thermodynamic specific features also cause the differences in the mechanisms of carbide precipitation from the α and γ phases in the absence of silicon redistribution: only cementite can precipitate from austenite, whereas both cementite and ε carbide can precipitate from bainitic ferrite.     

Effect of mechanical activation on the characteristics of ruthenium and aluminum powder mixtures

The effect of treatment in a high-energy mill-attritor on the structure of RuAl-based alloy powder mixtures and the exothermic effects in them is studied. The mechanical activation (MA) of aluminum and ruthenium powder mixtures is found to mill the conglomerates of hard disperse (0.5–2 μm) ruthenium particles in the initial mixtures and to produce composite granules. These granules consist of hard disperse ruthenium particles connected by plastic fcc aluminum particles. The structure of these granules differs from that of the layered granules that form during the MA of powder mixtures of two plastic fcc metals (nickel, aluminum). The cold working of the hard ruthenium particles, which have the hcp lattice and are deformed via twinning, occurs due to a decrease in the coherent domain size (to 120–80 nm) rather than to an increase in the dislocation density (as in the case of the MA of Ni-Al powders). Every granule contains all alloy (composite) components, including disperse or nanosize oxide particles, bound to the components that form an intermetallic matrix during reaction sintering. In granules of both types, MA increases the contact area between both metals entering into the reaction of RuAl (NiAl) formation and sharply decreases the diffusion path length of Al in Ru (Ni). This results in a decrease in the temperature of the onset of reaction alloy formation, which begins now in a solid phase, and in a decrease in the exothermic effect of the monoaluminide formation with the participation of a liquid phase (Al). MA for 15–16 h of powder mixtures provides a microuniform distribution of base and alloying elements and phases in the deformable alloys with an intermetallic matrix that are produced by reaction sintering.     

Atomic ordering in the phases of a nickel-chromium-based superalloy

The distribution of alloying atoms over the sites of the ordered crystal lattices of the γ′ phase and the Ni₂Cr superstructure that form during aging of the EK78 superalloy is determined by neutron diffraction, and their long-range order parameters are measured. The size, shape, and orientation of the forming γ′-phase precipitates and the ordered matrix are determined by electron microscopy. The mechanism by which the ordered phases in the EK78 alloy form during complex heat treatment is described.     

Determination of matrix dependences between the magnetic and elastoplastic characteristics of steels during tension

Stress-strain and coercive force-strain diagrams are experimentally obtained for grade 45 and St3 steels. These diagrams are used to construct matrix dependences between the elastoplastic and magnetic properties of the steels in order to determine the level of stresses in construction members made of these steels.     

Behavior of carbon,oxygen, and sulfur during hydrogen blowing of liquid steel

The decarburization of liquid steel during hydrogen blowing has been studied. The decarburization is caused by the interaction of carbon with oxygen dissolved in the metal. As the melt is blown with hydrogen, the decarburization is enhanced owing to hydrogen bubbles, which increase the effect of mixing of a metal bath and substantially increase the melt-gas phase interface. As a result, the rate and completeness of decarburization increase significantly. It is experimentally shown that hydrogen blowing of a melt substantially decreases the sulfur concentration in the metal because of the interaction of hydrogen with sulfur.     

Role of silicon in the formation of the corrosion resistance of austenitic materials for cryogenic engineering

The effect of silicon on the operational efficiency and corrosion resistance of low-temperature equipment made of 12Kh18N12T chromium-nickel steel has been studied. The specific features of the cryogenic equipment consist in high-temperature heating procedures between operation periods. Equipment for gas liquefaction and cleaning aimed at the restoration of the operational efficiency of filtration and catalysis systems serves as an example. The heating temperature of this equipment can reach 800°C. Experimental steels containing 0.09–1.03 wt % Si are subjected to intercrystalline corrosion tests. Upon heating to 550–600°C, silicon is found to increase the corrosion resistance of the steel, and, upon heating at higher temperatures, silicon plays a negative role. This is caused by the distribution of silicon atoms along grain boundaries, namely, a nonuniform silicon distribution with the formation of high-and low-concentration regions, i.e., the formation of clusters of silicon-phase preprecipitates.     

Mechanism of the structure formation of the transition layers in cobalt films electroplated on copper

The structure formation of the transition layers in electrolytic cobalt films on copper substrates is studied. It has been found that epitaxial growth and repeated twinning in the transition film/substrate layers form the nonequilibrium α and β cobalt phases, which cause additional reflections in electron and X-ray diffraction patterns.     

Aluminum hydroxide nucleation kinetics and mechanism during the electrodialysis decomposition of aluminate solutions

The kinetic laws of the electrodialysis decomposition of strong aluminate solutions are considered. Mathematical simulation is performed using the equations of the heterogeneous kinetics of aluminum hydroxide precipitation for the electrodialysis of aluminate solutions, and this simulation shows that the nature of the limiting stage is related to the instantaneous nucleation during the three-dimensional coalescence of particles. The electrodialysis precipitate is analyzed, and the possible commercial application of the decomposition of strong aluminate solutions by electrodialysis is considered.     

Applicability of the laws of elasticity for the determination of the elastic-region length in the deformation zone during cold rolling

The errors of calculating the energy-force parameters of cold rolling are analyzed. They appear because of the assumption of the classic rolling theory about the applicability of the Hertz formula, which is known in the theory of elasticity, to the calculation of the elastic-region length in the deformation zone. The Hertz formula, which is used to calculate the half-width of the contact area between a fixed cylinder and a plane that bounds an elastic half-space, is shown not to take into account the following factors that are characteristic and important for the roll-strip contact: the cold working of the strip, the strip thickness, the rotation of rolls accompanied by sliding friction, and the wear that decreases the initial roll roughness (i.e., changes in the friction coefficient). A method is proposed for taking into account these factors in the calculation of the energy-force parameters of cold rolling; it is based on the statistical processing of the parameters that are measured in operating mills and are present in the databases of their process control systems. The application of this method decreases the errors of calculating the rolling forces by 35–40% and refines some laws of the state of stress in a rolled strip.     

Electron-microscopic study of the slip systems in an Mg-4.5% Al-1% Zn alloy

Samples of a hot-rolled Mg-4.5% Al-1% Zn alloy plate cut normal to the rolling direction are studied to determine the density of dislocations with different Burgers vectors after warm rolling at low total strains. In the experiment, 22 different grains and their orientations are studied in a JEM-1000 high-voltage transmission electron microscope at an accelerated voltage of 750 kV using the WB DF technique (g, ng, where n = 2, 3, …) for the observation of dislocations. The main method used for the analysis of the Burgers vector of the dislocations is the invisibility criterion gb = 0. In the samples, dislocations with Burgers vectors 〈a〉, [c], and 〈a + c〉 are found. The dislocation dissociation reaction of the 〈a + c〉 dislocation into the 〈a〉 and [c] dislocations has been found for the first time, and an assumption is made that all of the found [c] dislocations result from this reaction. The density of the basal and nonbasal 〈a〉 dislocations does not depend on the orientation of the grains. Rarely found [c] and 〈a + c〉 dislocations are in grains whose orientations are near the texture maximum in the {0002} pole figure.     

X-ray diffraction study of the structural evolution in a grade 1469 (Al-Cu-Li) alloy during the production of hot-rolled sheets

X-ray diffraction is used to study the structural changes in a grade 1469 (Al-Cu-Li) alloy with a high lithium content that occur during the production of hot-rolled sheets according to the ingot → pressed strip → hot-rolled sheet schedule. In the pressed strip, a multicomponent Bs {110}〈112〉, Cu {211}〈111〉, and S {123}〈111〉 texture forms, which is typical of articles pressed from such alloys, and an unusual intense single-component texture of the Ex₁ {011}〈111〉 type forms in the hot-rolled sheets. Its formation is stimulated by cross rolling of the sheets. The low strength characteristics of the hot-rolled sheets after heat treatment are related to an elevated heating temperature used for quenching and to the oriented precipitation of the lamellar particles of the hardening T ₁ phase.     

Experimental and theoretical study of the effect of hydrogen on the creep and long-term strength of VT6 titanium alloy

The effect of the concentration of preliminarily introduced hydrogen on the creep and long-term strength of VT6 (Ti-6Al-4V) titanium alloy is studied experimentally and theoretically at a temperature of 600°C and nominal stresses of 47–217 MPa. Tests show that the presence of hydrogen in the titanium alloy (to 0.3 wt %) increases the time to failure and decreases the steady-state-creep rate and the ultimate strain by several times. A kinetic theory is used to simulate creep up to failure. The specific features of the macroscopic characteristics of creep are studied along with the evolution of the structural state of the alloy.