Powder Metallurgy and Metal Ceramics (v.47, #1-2)

Grigorii Samsonov (1918–1975) by I. I. Timofeeva; L. F. Pryadko (1-2).

The paper outlines comprehensive research of the physical and technical properties possessed by monocarbides of transition metals from groups IV and V of the Periodic Table within their homogeneity region. Experimental results are interpreted.
Keywords: refractory carbide; transition metal; carbon sublattice

The major principles of Samsonov’s quasichemical configuration model are discussed in terms of the many-electron theory of condensed systems. It is shown that the interrelation between the order of the s-and d-levels in isolated atoms of transition elements and the occupation of the corresponding bands in metals can be interpreted with quasiparticle theory that takes the d-d-and s-d-electronic correlations into account more accurately than ordinary one-electron theory does.
Keywords: matter; material; phase; electron state; phase stability; property

The cohesive energy of transition metals and its contributions related to the s-and d-electrons are calculated. The correlation of interatomic bonding strength, molar volume, and compressibility of transition metals with cohesion energy and corresponding contributions to it is shown. It is demonstrated that the s-electrons play an important part in the cohesion of transition metals. The main contributions to the formation energy of disordered alloys of copper with transition metals are calculated using the tight-binding approach. The results obtained are in qualitative agreement with experimental data on the thermodynamic properties of Cu-3d-metal systems.
Keywords: cohesive energy; tight-binding approach; transition metals; copper-based alloys; formation enthalpy of alloy

Sintering of mechanically activated Zno-TiO2 powders by N. Labus; S. Stevanovic; M. M. Ristic (40-46).
Zinc oxide and titanium dioxide powders mixed in an equimolar ratio are mechanically activated in a planetary ball mill and sintered under nonisothermal and isothermal conditions. Nonisothermal sintering is studied using dilatometry and SEM. The activation energy of sintering is determined using the method based on different heating rates and Dorn’s method as well. The phase composition of the isothermally sintered samples is determined using x-ray powder diffraction.
Keywords: sintering; mechanical activation; zinc metatitanate

Making and structural features of Ti-N-B and Ti-N-C nanocomposites by A. I. Bykov; I. I. Timofeeva; L. A. Klochkov; A. V. Ragulya; L. P. Isaeva; V. S. Urbanovich; M. M. Ristic (47-53).
The paper examines the high-pressure sintering of nanograined ceramic polycrystals based on TiN-TiB2 and TiC0.5N0.5 refractory compounds. Using the optimum pressure (up to 4 GPa) allows keeping the initial nanostate (TiN-TiB2 and TiC0.5N0.5) and obtaining high-density ceramics with enhanced mechanical properties. An x-ray structural analysis is used to examine how the TiN-TiB2 and TiC0.5N0,5 crystalline structure evolves during temperature-pressure treatment, which produces new ceramic materials. Based on the properties of the polycrystalline materials obtained, the temperature-time mode for the consolidation of initial nanopowders is determined to ensure favorable parameters of sintered nanograined ceramics.
Keywords: sintering; high pressure; refractory compounds; nanoceramics

The paper examines the structurization and stress state of ion-plasma condensates of Ti-W-B refractory materials exposed to radiation in deposition. High imbalance is found, which is characteristic of materials condensed with ion bombardment, the mean atomic energy of film-forming particles ranging from several to several tens of electron volts. Models for optimizing the structure and stress state of condensates exposed to radiation to improve their mechanical properties are discussed.
Keywords: ion-plasma condensate; low-angle x-ray dispersion; stress state; nanocrystalline coatings; nanostructured condensates; x-ray analysis

Analysis of nonisothermal sintering of zinc-titanate ceramics doped with MgO by N. Obradovic; S. Stevanovic; M. M. Ristic (63-69).
The aim of this work is to analyze nonisothermal sintering of zinc titanate ceramics doped with MgO obtained by mechanical activation. Mixtures of ZnO, TiO2, and MgO (0, 1.25, and 2.5%) are mechanically activated for 15 min in a planetary ball mill. Nonisothermal sintering is performed in air for 120 min at 800, 900, 1000, and 1100 °C. Microstructure parameters are revealed from an approximation method. Structural characterization of ZnO-TiO2-MgO system after milling is performed at room temperature using XRPD measurements. The main conclusions are that mechanical activation leads to the particle size reduction, the increase of dislocation density, and lattice strain. Doped zinc titanate samples achieve higher densities after sintering and the diffusion mechanism is dominant during the sintering process.
Keywords: milling; sintering; XRPD; ZnO-TiO2 system

A system approach to controlling the quality of detonation-sprayed coatings is developed. It includes such stages as selecting powder characteristics and gas composition, forming a gas-powder mixture, adjusting the parameters of two-phase pulse flow, and ensuring contact interaction needed to form the coating that depends on the material and preset service properties of the layer sprayed.
Keywords: coating; detonation-sprayed coating; particle velocity and temperature; layer formation; properties of coatings

The paper reviews the relevant literature and results of the author’s research into self-propagating high-temperature synthesis (SHS) used to deposit protective thermal-sprayed coatings. The compositions of different SHS-produced powders, which are used to deposit thermal-sprayed coatings, are indicated. The combination of spraying and synthesis of the material to form coatings by the interaction of composite powder particles is considered.
Keywords: thermal-sprayed coating; self-propagating high-temperature synthesis; powders; coatings; wear resistance

Mechanical and tribological properties of TiN and SiCN nanocomposite coatings deposited using methyltrichlorosilane by V. I. Ivashchenko; O. K. Porada; L. A. Ivashchenko; I. I. Timofeeva; S. M. Dub; P. L. Skrinskii (95-101).
The paper examines nanocomposite coatings based on TiN and SiCN obtained by plasma-enhanced chemical vapor deposition (PECVD) using methyltrichlorosilane (MTCS) as one of the precursors. The nanocomposite coatings demonstrate four types of structures depending on deposition modes: nc-TiN, nc-TiN/a-SiCN, nc-TiNC/nc-TiSi2/a-SiCN, and nc-TiNC/nc-TiCl2/a-SiCN. The nanohardness and elastic modulus of the coatings reach 31 and 350 GPa, respectively. The coatings on substrates of hard alloys, high-speed steel, and silicon increase the nanohardness of the base from 10 to 100%. The correlation between the H/E ratio and wear resistance is not observed. The coatings deposited at low radiofrequency powers demonstrate good adhesion to silicon substrates. It is shown that the use of MTCS as the main precursor allows one to obtain hard and wear-resistant nanocomposite coatings.
Keywords: nanocomposite coatings based on TIN and SiCN; chemical vapor deposition; plasma; methyltrichlorosilane; x-ray analyses; nanohardness; tribological properties; microabrasive wear

The velocity and temperature of particles resulting from the electrospark erosion of the anode are assessed. A mathematical model is developed to describe the mechanical interaction of particles with the substrate. The deformation and heat exchange between the substrate and copper and tungsten carbide particles with different initial temperature and velocity are calculated. Data on the final deformation, crystallization and cooling time of the particles, and the probability of their adhesion with the substrate are obtained.
Keywords: electrospark alloying; spark-erosion products; high-speed impact; deformation dynamics; heat exchange with substrate

Contribution of electrospark alloying to the oxidation resistance of hard tungsten alloys by A. D. Verkhoturov; A. M. Shpilev; P. S. Gordienko; L. A. Konevtsov; E. S. Panin; I. A. Podchernyaeva; A. D. Panasyuk (112-115).
The paper examines the contribution of electrospark alloying to the oxidation resistance of hard tungsten alloys. It is established that the oxidation of carbides results from their electronic structure. When WC and hard tungsten alloys are heated to 1000°C, a brittle scale consisting of WO3 and CoWO4 rapidly forms. The oxidation resistance reduces as follows: TiC → Co → W → HTA (if TiC is more than 10%) → WC-Co → WC. The oxidation rate of hard tungsten alloys may be a criterion of their serviceability. It is shown that the oxidation resistance of hard tungsten alloys becomes much higher after their electrospark alloying with aluminum, titanium, and chromium and with wear-resistant composite TsLAB-2 ceramics based on the ZrB2-ZrSi2-LaB6 system with Ni-Cr-Al (30 mole%) binder.
Keywords: hard tungsten alloys; carbides; electron structure; oxidation resistance; oxidation; electrospark alloying; ceramics

Electroerosion resistance and structural phase transformations in electrospark and laser deposition of titanium alloys using composite ceramics based on ZrB2-ZrSi2 and TiN-Cr3C2 systems by I. A. Podchernyaeva; A. D. Panasyuk; V. M. Panashenko; O. N. Grigor’ev; V. G. Kayuk; V. P. Stetsenko; A. M. Bloshchanevich (116-123).
The paper examines the mass transfer kinetics, structure, phase and chemical compositions, and micromechanical properties of electrospark and laser coatings on titanium alloys (including their combination) deposited using composite materials based on the ZrB2-ZrSi2 and TiN-Cr3C2 systems. The electrospark deposition of both materials is characterized by a relatively high mass-transfer coefficient (∼40–60%) over a wide range of treatment time t ≥ 1 min/cm2. It is determined that after prolonged electrospark deposition (t = 7 min/cm2), ZrB2-ZrSi2 coatings have structurally heterogeneous surface with smoothed Ti-alloy localities caused by the melt crystallization and modified with alloying components. It is shown that ZrB2-based coatings are promising along with conventional wear-resistant coatings based on refractory titanium compounds.
Keywords: electrospark alloying; laser alloying; composite material; coating; phase composition

Growth kinetics of SiO2 nanofilm on MoSi2 in anodic polarization by V. A. Lavrenko; A. D. Chirkin; V. N. Talash; A. D. Panasyuk (124-128).
The anodic oxidation of MoSi2 ceramics in 3% NaCl solution is shown to be a multistage process. Auger electron spectroscopy established that only silica forms on the MoSi2 surface between 1.5 and 2.0 V, while molybdenum passes completely into solution. The growth kinetics of silica is studied using chronoamperometry under controlled potential conditions. The resulting kinetic curves show two stages. At the first stage, the reaction rate (current density) falls by one order for the first few minutes when SiO2 nanofilm begins to form. Then the diffusion-limited process, which fits parabolic kinetics, is established. On the whole, the model describing the electrochemical formation of oxide nanofilm on molybdenum disilicide agrees with the Mott-Cabrera theory, which was earlier proposed for high-temperature oxidation processes.
Keywords: MoSi2 ; anodic oxidation; silica film; diffusion; parabolic kinetics; Mott-Cabrera theory

High-temperature friction of refractory compounds by Yu. G. Tkachenko; D. Z. Yurchenko; M. S. Koval’chenko (129-136).
The paper overviews long-term studies into the behavior of metallic (carbides, borides, and nitrides of transition metals), and nonmetallic (boron and silicon carbides, aluminum nitride) refractory compounds as well as composite materials based on them in high-temperature friction in vacuum and air. The friction characteristics (wear rate and friction coefficient) are indicated as a function of temperature in the range from room temperature up to 1000–1400 °C. Data of x-ray examination and electron microscopy of friction surfaces are cited. The fracture mechanism for contacting surfaces of materials in friction is considered.
Keywords: refractory compounds; friction; wear; high temperature; surface structure

Recent studies on oxidation kinetics of the TiC-7 vol.% C (graphite) hetero-modulus ceramics at temperatures of 400–1000 °C and oxygen pressures of 0.13–65 kPa have led to the discovery of a temperature-pressure-dependent phenomenon called “ridge effect”. The oxidation rate of the composite rises rapidly to a maximum at ridge values of oxygen pressure $$(p_{0_2 } )$$ or temperature (T), but then it declines with subsequent growth of oxidation parameters. The ridge values mark a change in the prevailing mechanism, as while the ridge parameter traversing the values of apparent activation energy Q or order of reaction m change its sign. The oxidation mechanisms, essentially different within the ranges of parameters, are identified according to the developed ridge-effect model, which can be applied probably to a variety of systems with inorganic compounds.
Keywords: high-temperature materials; refractory compounds; titanium carbide; graphite; composites; hetero-modulus ceramics; oxidation; chemical properties; thermogravimetric analysis; x-ray diffraction

High-temperature oxidation of composite AlN-ZrB2-ZrSi2 ceramics by V. A. Lavrenko; A. D. Panasyuk; I. A. Podchernyaeva (151-156).
The high-temperature (to 1450°C) oxidation of AlN-ZrB2-ZrSi2 powders and compact ceramic materials with different contents of ZrB2-ZrSi2 solid solution in air is examined using scanning electron microscopy and differential thermal, thermogravimetric, x-ray phase, and x-ray spectrum microanalyses. It is established that the hot-pressed (practically porousless) ceramic materials have high corrosion resistance up to 1350–1400°C when scale components (individual oxides) interact with each other to form solid solutions based on aluminum oxide, zirconium oxide, and aluminum borate. These phases become sintered in the presence of the liquid B2O3 phase, self-reinforced scale being formed.
Keywords: composite ceramics; aluminum nitride; zirconium boride; zirconium silicide; high-temperature oxidation; self-reinforced scale