Powder Metallurgy and Metal Ceramics (v.53, #5-6)

Structure and Properties of β-Rhombohedral Boron Powders Produced by Mechanical Grinding by D. L. Gabuniya; O. A. Tsagareishvili; L. S. Chkhartishvili; Z. M. Miridzhanashvili (251-261).
The paper analyzes and summarizes the results from studies on the structure and the mechanical, chemical, and process properties of size-classified β-rhombohedral boron powders produced by mechanical grinding. The influence of certain grinding factors on some characteristics (pycnometric and bulk densities, yielding, amplitude of EPR signals, and reactivity) are evaluated. Methods for the removal of impurities from ground powders, storage, and XRD testing of fine fractions are proposed. The research results are used to develop a process to produce β-rhombohedral boron powders of different particle sizes with stable structure and physical and processing characteristics. It is established that individual powder fractions can be used as additions to abrasive diamond micropowders and for the formation of neutron-absorbing coatings on various materials and articles.
Keywords: β-rhombohedral boron; grinding; powder; size classification; structure; mechanical; chemical; and processing properties; production process

The Preparation of Zeolite/Ag Composite Powders by Electroless Deposition Process by M. Uysal; R. Karslioglu; H. Gul; S. Aslan; S. Y. Keskin; S. C. Okumus; A. Alp (262-268).
Core-shell Ag-coated zeolite composite powders were synthesized using silver electroless deposition process, which was carried out in an ammonia-based coating solution containing silver nitrate as a precursor material. The influence of the chemical components and powder concentration in the Ag coating was investigated by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction techniques. The zeolite/Ag composite powders were fabricated in order to find an antibacterial material and a new implant material based on the microstructural change of zeolite/Ag composites powders using different parameters of Ag deposition.
Keywords: electroless Ag coating; alkaline solution; core–shell structure; zeolite powder

The superposition of reaction waves, leading to energy concentration in local regions, is revealed in studying the thermal kinetics of interaction in mixtures with exothermic reactions during contact melting. The local energy relaxes through spontaneous emission of charged particles. This influences the thermal electromotive force and allows the dynamics of reaction wave interaction to be followed in the process. In these cases, synthesis and reaction sintering are uncontrolled.
Keywords: powder system; exothermic reaction; concentration and heat waves; superposition; synthesis; sintering

Microstructure and Abrasive Wear Behavior of CuSn10–Graphite Composites Produced by Powder Metallurgy by A. Canakci; H. Cuvalci; T. Varol; F. Erdemir; S. Ozkaya; E. D. Yalcin (275-287).
In this study, CuSn10 metal-matrix composites (MMCs) reinforced with 0, 1, 3, and 5 vol.% graphite particulates were fabricated by powder metallurgy. The microstructure, relative density, hardness, and abrasive wear behavior of the composites were investigated. The abrasive wear tests were conducted on unreinforced matrix and CuSn10–graphite composites using a pin-on-disk-type machine. The effects of sliding distance, applied load, graphite particle content, and abrasive grit sizes on the abrasive wear properties of the composites have been evaluated. The microstructure evolution of composites and the main wear mechanisms were identified using a scanning electron microscope and an energy-dispersive X-ray spectrometer (EDS). The density and hardness of the sintered CuSn10–graphite composites decreased with increasing graphite content. The abrasive wear resistance increased with increasing graphite content, but the abrasive wear resistance decreased with increasing sliding distance, applied load, and abrasive grit size. Moreover, the wear resistance of the composite was found to be considerably higher than that of the CuSn10 matrix alloy and increased with increasing graphite particle content.
Keywords: abrasive wear; CuSn10 matrix composites; powder metallurgy; graphite particle

Consolidation of Non-Conductive Cutting Elements of Abrasive Tool by M. V. Luchka; O. V. Derevyanko; M. S. Kovalchenko; M. V. Kindrachuk (288-293).
The conditions for cladding of diamond and superhard macropowders with composite electrolytic coatings are studied. The coating characteristics are established to depend on the pretreatment, electrolyte concentration, current density, and deposition duration. The optimal coating layer 120–150 μm in thickness is produced at a current density of 2.5–3 kA/m2. The conditions for making composite materials from diamond-like clad powders by filed-associated sintering are examined. It is shown that current density and heating rate are the determining factors. The properties of a composite material become optimal at a current density of 8.28 · 106 A/m2 and a total sintering time of no longer than 120 sec. Tools made from such composite materials can be used for machining granite and marble. The performance of composite materials produced from clad superhard diamond macropowders is higher than that of materials from a mixture of cobalt and diamond powders.
Keywords: cladding; macropowders; galvanic powder strengthening; cutting tools; sintering

The paper examines the effect of additions (TiO2, TiH2, TiN, and TiC up to 4 vol.%) and isothermal holding temperature on the dielectric properties of hot-pressed AlN ceramics in a wide frequency range. It is established that the service characteristics of AlN–TiO2 ceramics show a parabolic dependence on titanium oxide additions: optimal porosity (0.1%), permittivity (9.7), and dielectric loss tangent (1.3 ⋅10−3) are reached with 0.5 to 2 vol.%. TiO2. Additions of TiH2 promote the formation of metallic films, mainly oriented along the pressing direction. The deviation of sintering temperature from the optimal value increases conduction-induced losses since structures with more defects and conducting phases form. It is shown that broadband (103–107 Hz) dielectric spectroscopy can be used to monitor the composite’s microstructure: the frequency of migration polarization dispersion provided information on the effective thickness of the conducting channel and the slope σ(ω) allowed the lattice and jump responses to be differentiated.
Keywords: aluminum nitride; hot pressing; nondestructive examination; defects; dielectric response; polarization

Phase Diagrams of Refractory Oxide Systems and Microstructural Design of Materials by E. V. Dudnik; S. N. Lakiza; Ya. S. Tishchenko; A. K. Ruban; V. P. Red’ko; A. V. Shevchenko; L. M. Lopato (303-311).
It is shown that the phase diagrams of refractory oxide systems based on ZrO2, HfO2, Al2O3, and rare earth oxides underlie the microstructural design of various high-performance materials. Process steps to produce coarse-grained ceramics in the HfO2–ZrO2–Y2O3, ZrO2–Y2O3–Sc2O3, HfO2–ZrO2–Sc2O3, Y2O3–Er2O3, Y2O3–ZrO2, Y2O3–HfO2, Y2O3–Al2O3, Y2O3–SiO2, and Y2O3–La2O3 systems to perform at temperatures up to 2200°C are designed. Process steps to produce high-performance fine-grained composites in the HfO2–ZrO2–Y2O3 (Ln2O3) (Ln–Dy, Ho, Er, Tm, Yb), ZrO2–Y2O3–Sc2O3, ZrO2–Y2O3–Sc2O3, Al2O3–Zr(Hf)O2–Ln(Y)2O3 (Ln–La, Nd, Sm, Gd, Er, Yb), and ZrO2–Y2O3–CeO2–Al2O3 systems are designed as well.
Keywords: ZrO2 ; HfO2 ; Al2O3 ; rare earth oxides; phase diagrams of refractory oxide systems; highperformance materials; mechanical properties

Liquidus Surface of the ZrO2–Y2O3–Eu2O3 Phase Diagram by E. R. Andrievskaya; V. V. Kovylyaev; L. M. Lopato; A. V. Shevchenko; A. A. Frolov (312-322).
The derivative thermal analysis in air up to 3000 °C, X-ray diffraction, petrography, and electron microscopy are employed to examine phase equilibria on the liquidus surface of the ZrO2–Y2O3–Eu2O3 phase diagram. It is established that the liquidus surface of the system is formed by four primary solidification fields of the phases: solid solutions based on hexagonal (N) and cubic (C) crystalline modifications of Y2O3, cubic ZrO2 modification with fluorite (F) structure, and high-temperature cubic modification (X) of Eu2O3. Two four-phase invariant incongruent equilibria are found in the ternary system.
Keywords: phase equilibria; liquidus surface; phase diagram; zirconium oxide; yttrium oxide; europium oxide

Comparison of the isothermal sections in similar Al2O3–ZrO2–La2O3 and Al2O3–HfO2–La2O3 systems shows that equilibria between the α-Al2O3, Hf(Zr)O2, La2Zr2O7, La2Hf2O7, and LaAlO3 phases in these systems differ fundamentally. While the ZrO2−LaAlO3 equilibrium is observed in the system with ZrO2, the alternative La2Hf2O7–Al2O3 equilibrium takes place in the system with HfO2. The triangulation in the system with HfO2 changes. This phenomenon is probably due to higher thermodynamic stability of the La2Hf2O7 phase (melting point 2420°C) compared to the similar La2Zr2O7 phase (melting point 2280°C). Other equilibria in both systems are of the same type. Lanthanum hafnate can be directly deposited onto the binding coating without reacting with α-Al2O3 or destroying the thermal barrier coating. Stable performance of the lanthanum hafnate coating is expected.
Keywords: ceramics; zirconia; hafnia; alumina; lanthana; isothermal section; phase diagram; thermal barrier coating

Interaction Between ZrB2–MoSi2 Cermets and Oxide Melts by A. D. Panasyuk; O. N. Grigoriev; A. V. Koroteev (330-334).
Contact interaction of ZrB2–MoSi2 materials with oxide melts is studied. The oxide melts are formed during combustion of low-reaction coals containing 30–49% oxides. It is established that ZrB2–MoSi2 composites are wetted by oxide melts (contact angles being 21–5° depending on material composition) at 1600–1700°C in wetting conditions as well as during interaction for 6 h. A thin layer (~5–15 μm) forms in the contact zone, SiO2 and ZrO2 being its main phases. There are a great number of MoO3, CaO, and Fe2O3 oxides at the boundary of these phases. The contact layer serves as a film protecting the composite against further corrosion in oxide melts. The optimum composition of ZrB2–MoSi2 ceramics, which is resistant to corrosion in oxide melts, is determined.
Keywords: composite ceramics; ZrB2–MoSi2 system; wetting; contact interaction; phase composition; composite–melt interface

Magnesium Composites with Additions of Oxygen-Stabilized η-Zr4Fe2O0.5 for Effective Hydrogen Accumulation by V. V. Berezovets; R. V. Denis; I. Yu. Zavaliy; V. Paul-Boncour (335-342).
The advantages of reactive ball grinding for preparation of new efficient Mg-based hydrogen storage materials are discussed. Magnesium-based nanocomposites were synthesized with additions of η-Zr4Fe2O0.5 intermetallic compound, which is characterized by enhanced resistance to disproportionation in hydrogen and can prolong the cyclic life of materials. The improvement of hydrogen absorption parameters for Mg–intermetallic composites was observed. It was shown that fourfold increase in the reaction rate during mechanochemical synthesis of MgH2 and decrease in hydrogen desorption temperature by 80°C were induced by catalytic additions.
Keywords: hydrogen; hydride; magnesium; composite; mechanochemical synthesis

Differential thermal analysis and X-ray diffraction are used to study phase transitions in the Sm2Co17–xFex–H2 system (x =3.9 and 5.95) during conventional and solid HDDR at hydrogen pressure 0.57–4.0 MPa and temperature up to 950°C. The ferromagnetic phase with Th2Zn17 structure disproportionates into SmH2±x, cobalt, and intermetallic FeCo after one-hour interaction with hydrogen at 1.1 and 0.6 MPa and 700°C with x =3.9 and 5.95. Recombination in vacuum at 770–950°C leads to a two-phase alloy consisting of the Th2Zn17-type phase and intermetallic FeCo.
Keywords: hydrogenation, disproportionation, desorption, recombination; samarium–cobalt alloys; two-phase ferromagnetic materials

Production of Ti–Al–Si–B–N Films by Magnetron Sputtering and Study of Their Mechanical Properties by A. A. Onoprienko; V. I. Ivashchenko; I. A. Podchernyaeva; O. Yu. Khizhun; I. I. Timofeeva; O. A. Butenko (353-358).
The Ti–Al–Si–B–N films are deposited by dc magnetron sputtering of a composite Ti–Al–Si–B–N target in argon plasma. The structure and phase composition of the films were studied by X-ray diffraction. The chemical bonds in films were examined by X-ray photoelectron spectroscopy. The influence of vacuum annealing on film structure, hardness, and mechanical properties was analyzed. The films deposited at temperatures in the range 200–500°C and bias voltages of 0…–250 exhibited amorphous structure, which was preserved during annealing up to 800°C. At higher annealing temperatures, nanocrystalline phases started to form in the films. Annealing also resulted in increase of hardness and improvement of mechanical characteristics of the films.
Keywords: magnetron sputtering; nanocomposite; structure; mechanical properties

Structurization of Composites from Self-Fluxing Alloys with Titanium Diboride Additions by A. P. Umanskii; A. E. Terentiev; M. S. Storozhenko; I. S. Martsenyuk (359-367).
The structurization and phase interaction during sintering of the Ni–Cr–B–Si–C–TiB2 composite are studied. X-ray diffraction, scanning electron microscopy, electron microprobe analysis, and metallography are used to examine the effect of 10–40 wt.% titanium diboride additions on the structure and phase composition of the material and powders for thermal spray coatings. It is established that titanium diboride additions lead to the formation of new complex Cr(Me)23C(B)6 phases with microhardness 18–19 GPa and TiC phase. The size and content of these phases can be controlled by changing the amount and size of additions and sintering conditions. The optimum amount of TiB2 promoting high service properties is 20 wt.%. The new phases formed in the composite constitute 30 vol.% and their size is between 1 and 20 μm. It is possible to control the service properties of Ni–Cr–B–Si–C–TiB2 composites and thermal spray coatings by changing the structural and phase composition of the powder material.
Keywords: composite; self-fluxing alloy; structure; phase composition; titanium diboride; microhardness; thermal spray coatings

The experience in designing aircraft components for lightning protection was employed to develop knitted soldered meshes to decrease damage of composites used to make wind blades to benefit from improved dissipative properties. Conductive nanostructured carbon modifiers are proposed to improve the electric conductivity of carbon fiber-reinforced plastic laminates and enhance the adhesion strength between the carbon fibers and binder. Knitted soldered copper meshes are suggested to improve the lightning protection of wind turbine blades (lightning arresters and down conductors). The research results will be useful for overall efficient lightning protection of wind turbine blades.
Keywords: polymer; composites; binder; knitted soldered meshes; nanostructured particles; lightning protection