Powder Metallurgy and Metal Ceramics (v.56, #3-4)

The features of dissolution of briquetted powder inoculants with different compositions (92% Fe–8% Mg; 42% Fe–8% Mg–50% Cu, and 92% Cu–10% Mg) in a cast iron melt, including their densities and geometric characteristics, are investigated. It is shown that the dissolubility of briquetted inoculants in the melt decreases with increasing porosity from 8 to 15%, while increases with increasing porosity up to 30%. The introduction of copper into the composition of briquetted inoculants enhances their dissolution intensity and degree of magnesium recovery by the cast iron melt. It is established that the application of Fe–Cu–Mg inoculants provides the maximum values of graphite particles shape factor and strength properties of the cast iron at optimal temperatures (1400 and 1420°C) of melt processing.
Keywords: high-strength cast iron; melt; powder; inoculant; porosity; dissolution; graphite; spheroidizing

Composite TiO2-based photocatalysts are studied. They increase the efficiency of water and air purification from toxic organic impurities and allow the synthesis of hydrogen by water photolysis and CO2 reduction to methane and its homologues. These processes are of huge scientific and practical interest because they are aimed at solving global energy conservation problems. The latest achievements in the production of composites with various polymer matrices and nanosized oxide particles are demonstrated. The properties of these materials and their potential applications are described. An alternative option is considered, such as modification of nanosized particles by substances of different natures, to improve the photocatalytic properties of TiO2 and shift the absorption spectrum into the visible light region. The positive and negative effects of impurities introduced into the TiO2 structure on the photocatalytic activity are addressed. The study of various additives influencing the optical and photocatalytic properties of TiO2 is among the priority areas in modern photochemistry.
Keywords: nanocomposite; nanosized particles; nanosized titanium oxide; polymer; properties; electrical conductivity; structure

The effect of milling time and addition of elements on the microstructure, magnetic and mechanical properties of the Fe–xCo (x = 0, 5, 10, and 20 wt.%) matrix nanocomposite reinforced with 40 wt.% Al2O3 during mechanical alloying is examined. Fe–Al2O3 and Fe–Co–Al2O3 alloys are milled for 5, 15, 20, and 30 h and 20 h, respectively. The balance between the welding and fracturing and a steady-state situation is found out in the Fe–Co–40 wt.% Al2O3 nanocomposite after 20 h, due to the Co introduction into the Fe matrix, but not in the Fe–Al2O3 nanocomposite. After 30 h of milling, the average crystallite size was 5 nm in the Fe matrix. The lattice strain increased to ~0.64% in the Fe matrix after ≤30 h of milling and in the binary Fe–20 wt.% Co matrix after 20 h of milling; the average crystallite size was 3 nm. The lattice strain increased to ~0.56% for the Fe–20 wt.% Co matrix after ≤20 h of milling. The coercive field (Hc) increased from 6.407 to 82.027 Oe, while the saturation magnetization (Ms) decreased from 20.732 to 15.181 emu/g in the Fe matrix during milling. The Hc and Ms are maximum for the binary matrix (20 and 10% Co, respectively).
Keywords: Fe–Co matrix nanocomposite; alumina; mechanical alloying; microstructural evolution; magnetic properties

Wear Resistance of High-Entropy Alloys by S. A. Firstov; V. F. Gorban’; N. A. Krapivka; M. V. Karpets; A. D. Kostenko (158-164).
The tribotechnical properties of high-entropy alloys in pair with 65G steel in air under dry sliding friction conditions are investigated in comparison with wear-resistant steel and powder materials. The sliding friction rate was 6, 8, and 12 m/sec and the pressure was 0.5 and 1.0 MPa. It is determined that the wear intensity of high-entropy alloys at the sliding friction rate 5–10 m/sec under 0.5 and 1.0 MPa loads ranges from 6.1 · 10–10 g/km to 1.6 · 10–9 g/km for the samples and from 5.5 · 10–8 g/km to 1.1 · 10–8 g/km for the counterface. It is established that, when friction, the shear deformations promote the formation of thermally stable nanostructures with grains 30–70 nm in size in the surface layer of the secondary structures. It is shown that the formation of nanostructures is accompanied with 20–30% increase in hardness for both high-entropy alloys and counterface material. It is established that, when friction, high temperatures at the contact points promote the formation of ordered β-phase with BCC lattice on the friction surface of the Fe25Cr20Ni20 Mn15Co10Al10 high-entropy alloy.
Keywords: high-entropy alloy; secondary structure; sliding rate; pressure; wear intensity; friction coefficient

The interaction processes in the Cr7C3–WO3 system during high-temperature heating are considered. It is established that the resulting powder products are characterized by a multicomponent composition, in which chromium carbide and complex carbides of chromium and tungsten dominate. The properties and structure of these fine-grained powder compositions (master alloys) are studied. It is established that the microstructure of alloyed samples based on powdered iron with the addition of developed master alloys is characterized by high homogeneity and dispersion with fibrous, rod, and lamellar nanoscale carbide formations. The density, microhardness, hardness, and wear resistance of alloyed samples are determined. The effect of developed master alloys on the abrasion wear resistance of alloyed metal matrix composites is established.
Keywords: chromium carbide; tungsten oxide; master alloy; metal matrix composite; wear resistance

W–Cu System: Synthesis, Modification, and Applications by Longlong Dong; Wenge Chen; Lintao Hou; Nan Deng; Chenghao Zheng (171-184).
W–Cu composites, as a traditional material, have attracted tremendous research interest in fields such as electric engineering, electronic information, aerospace, weapons, etc., owing to their excellent properties. This critical review presents and discusses the current development of W–Cu composites. After introduction of the synthesis methods for W–Cu composites, including the conventional and modern preparation approaches, we focus on the description of the improvement of mechanical properties and arc-erosion properties by modification techniques. Finally, the advantages of W–Cu composites in applications such as electrical contacts, electronic packaging materials, and heat sinks, as well as military materials, are described.
Keywords: tungsten–copper composites; preparation method; modification; application

Effect Of Formation Conditions of Thick Granular Films Based on Dispersed Co3b On Their Phase Composition and Magnetoresistance by B. M. Rud’; E. Ya. Tel’nikov; A. K. Marchuk; I. I. Timofeeva; K. A. Meleshevich; L. I. Fiyalka (185-190).
An important scientific and technical problem on developing thick resistive granular films used in microelectronics and tool manufacturing is solved. Magnetoresistive Co-containing granular films are obtained by screen printing the pastes consisting of fine-grained cobalt boride Co3B and organic binder on a dielectric substrate. Then, the deposited films are heat treated in air with no protection at all. Differential thermal analysis and thermogravimetric analysis reveal that only ferromagnetic Co (FCC) and amorphous B2O3 are present in the structure of the films at T = 650–850°C. On this basis, the modes for the heat treatment of films are developed. The effect of magnetic field on the electrical resistance of films is studied.
Keywords: film; heat treatment; differential thermal analysis; thermogravimetric analysis; magnetoresistive properties

DTA Research on Interfacial Contact in Fe–Al Powder Mixture by Yu. S. Borisov; A. L. Borisova; T. V. Tsymbalista (191-197).
The interfacial contact in exothermically reacting mixture of Fe and Al powders (or Al-alloy) designed for the formation of intermetallic Fe3Al powder is studied by differential thermal analysis (DTA). The effect of alloying elements such as Mg and Ti on this process is analyzed. The behavior of the Fe–Al-based powder produced by heating under DTA conditions is compared with that of the powder with the same composition produced by mechanochemical synthesis.
Keywords: powder mixture; Fe–Al system; intermetallic Fe3Al powder; differential thermal analysis; alloying; Mg; Ti; mechanochemical synthesis; phase composition; microhardness

Scientific publications on the methods of applying heat-resistant coatings to refractory metals, such as molybdenum, tungsten, niobium, tantalum, and their alloys, are analyzed. Vacuum-activated diffusion hardening is considered to be one of the most optimal methods of depositing protective coatings. For niobium and tantalum, a molybdenum or tungsten layer is required to be preliminary applied by one of the three methods: vapor-phase deposition, condensation, or ion bombardment. The materials used for the production of protective coatings are studied: silicides, refractory metal borides, high-temperature oxides, and enamels.
Keywords: refractory metals; silicon; boron; heat-resistant coatings; vacuum-activated diffusion hardening

The Quasibinary ZrCo–ZrNi Phase Diagram by O. L. Semenova; V. M. Petyukh; O. S. Fomichev (210-219).
Physicochemical analysis methods (metallography, X-ray diffraction, differential thermal analysis, and electron microprobe analysis) are used to first study the ZrCo–ZrNi alloys in the temperature range that includes their melting and crystallization. The phase diagram of the system is constructed. The phases based on ZrCo (crystal structure of CsCl type, maximum nickel solubility about 46 at.%) and ZrNi (crystal structure of CrB type, cobalt solubility about 2 at.%) coexist in a range from room to subsolidus temperatures. The phase diagram is of peritectic type with peritectic point coordinates 1240 ± 12°C and ~48 at.% Ni.
Keywords: cobalt; nickel; zirconium; phase diagram; transformation; peritectic reaction

Phase Equilibria in the Cu–Ti–Zr System at 750°C. II. The Isothermal Section with Copper Content from 50 to 100 at.% by A. M. Storchak-Fedyuk; L. V. Artyukh; A. V. Grytsiv; P. G. Agraval; M. A. Turchanin; T. Ya. Velikanova (220-230).
Alloys of the ternary Cu–Ti–Zr system with 50–100 at.% Cu, annealed at 750°C, are studied by scanning electron microscopy, electron microprobe analysis, and X-ray diffraction. The isothermal section at 750°C is constructed in this composition range. A new hexagonal ternary phase of composition Cu63.5Ti14.5Zr22 is found.
Keywords: Cu–Ti–Zr system; microstructure; isothermal section

The partial mixing enthalpies of titanium, zirconium, and hafnium with liquid copper and iron alloys are studied by high-temperature calorimetry. The studies are carried out at a temperature of 1873 K along the sections with constant ratios x Cu/x Fe = 3, 1, and 1/3. Along all the studied sections, these functions are negative. The integral mixing enthalpies of components in the Cu–Fe–(Ti, Zr, Hf) systems along the studied sections are calculated by integrating the Gibbs–Duhem equation. The ΔH functions for ternary Cu–Fe–(Ti, Zr, Hf) melts are characterized by positive values in the vicinity of the binary Cu–Fe system and show negative values in a range of compositions with x Me > 0.1 (Me = = Ti, Zr, Hf).
Keywords: mixing enthalpy; thermodynamic properties; alloys of copper and iron with titanium; zirconium; and hafnium; high-temperature isoperibolic calorimeter; amorphous alloys