Powder Metallurgy and Metal Ceramics (v.54, #3-4)

Improving Methods for Studying the Strain Distribution in Powders During Compaction by G. A. Baglyuk; V. S. Kurikhin; A. I. Khomenko; I. S. Kozachenko (129-135).
Methods for studying the cross-sectional distribution of density and strain in metal powder compacts are reviewed. A method for studying strain and density distribution during powder compaction is proposed. It involves layer-by-layer filling of the mold cavity with powders of identical composition, shape, and particle size but of different colors, (compaction, cutting of the compact, scanning the cutting plane, and digitization of its image. The application of the method proposed and the results of the digital processing of the image are presented.
Keywords: powder ; compaction ; density ; strain distribution ; porosity

Geometric Characteristics of Scaffolds Made by Additive Manufacturing by G. Ziolkowski; P. Szymczyk; B. Dybala; E. Chlebus; A. Pawlak (136-139).
Additive manufacturing (AM) allows producing objects with functional internal structures; one of their applications is the production of medical implants (scaffolds), which may substitute bone tissue. The aim of this study is to evaluate, by micro computed tomography (μCT), the geometric accuracy of scaffolds manufactured from Ti–6Al–7Nb alloy by selective laser melting (SLM). Micro-CT is a non-destructive method for investigating internal object structures. Its application in analysis of bone scaffolds allowed obtaining full geometric characterization of manufactured structures as 3D models and evaluation of the conformance of the scaffolds to their CAD designs. The influence of building direction during production of the quality SLM structures was also examined. Scaffold characteristics important for the application in tissue engineering, such as porosity and the actual surface area, were obtained. Validation of the μCT method, by examining selected cross-sections with a scanning electron microscope (SEM), proved that differences in dimensional characteristics of structures did not exceed 10 micrometers.
Keywords: additive manufacturing; medical implants; medical scaffolds; selective laser melting; tissue engineering

Formation of a Tribofilm in the Surface Layer of Al–Ti–Cr–N–B Magnetron Coating on Boron Nitride During Turning of Hardened Steel by I. A. Podchernyaeva; S. A. Klimenko; V. M. Beresnev; V. M. Panashenko; I. N. Toryanik; S. An. Klimenko; M. Yu. Kopeikina (140-150).
The effect of cutting ShKh15 hardened steel on the element and phase composition of the surface layer of the coating deposited on the cBN-based tool is studied. The microstructure and oxidation kinetics of the surface layer of the AlN–Ti(Cr)B 2 magnetron coating are investigated during both formation and turning. The coating is formed by HF magnetron sputtering of an AlN–Ti(Cr)B 2 target. The formation of a two-layer tribofilm with a nanosize outer layer is examined. The phase composition of the tribofilm is determined using layer-by-layer Auger analysis. Its outer nanosize layer is a glass-like phase in the form of limited solid solutions based on Al 2 O 3 oxides and playing a role of solid lubricant. As the cutting speed is increased, the wear rate for the coated tool decreases compared with the uncoated tool.
Keywords: cutting tool ; cubic boron nitride ; magnetron coating ; composite ceramics ; tribofilm ; wear resistance

Filtering Properties of Porous Materials Made of Thin Stainless Steel Fibers by O. V. Kirichenko; V. N. Klimenko; I. V. Shapoval; I. K. Valeeva (151-155).
The basic structural parameters of high-porous materials made by pressing and sintering 316L stainless steel fibers (diameter 6.5, 12.0, and 22.0 μm) and mixture (1 : 1) of fibers (diameter 6.5 and 30 μm) are determined using mercury porosimetry. The pore size and hydrodynamic properties of high-porous materials made by pressing and sintering 1Kh18N9T stainless steel fibers (diameter 10 μm) are determined. High-porous stainless steel fiber materials can be used for making regenerating fine filters for cleaning corrosive gases at high temperatures.
Keywords: high-porous fiber materials; filters; mercury porosimetry; stainless steel

Effect of Sintering Duration on Some Properties of Pure Magnesium by I. Gunes; T. Uygunoglu; M. Erdogan (156-165).
Tribological and physical properties of pure magnesium (Mg) are investigated during sintering for 2, 4, and 6 h at the temperature of 600°C. The pure sintered magnesium is characterized by wear behavior, corrosion, scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), unit weight, water absorption, specific weight, and micro-Vickers hardness testing. XRD analysis of sintered Mg revealed the existence of Mg, MgO, and MgO2 compounds. The hardness of the pure magnesium ranged from 53.8 to 70.4 HV0.1. The wear tests are carried out in a ball-disc arrangement under a dry friction condition at room temperature with an applied load of 5 N and a sliding speed of 0.2 m/sec at a sliding distance of 250 m. The wear surfaces of the Mg samples are analyzed using SEM and EDS. It is observed that the wear rate of pure Mg decreased by 54% when the sintering duration is increased. The corrosion resistance of Mg sintered for 6 h is increased by 36% compared to Mg sintered for 2 h.
Keywords: magnesium; water absorption; specific porosity; wear rate; corrosion

Solid Oxide Fuel Cell Anode Materials by E. M. Brodnikovskii (166-174).
The solid oxide fuel cell is a promising element that efficiently converts fuel chemical energy into electrical and thermal ones. The paper offers a brief overview of the ways for enhancing the properties of the anode by improving its composition and structure. The composition and structure of the anode are responsible for the electrochemical oxidation of fuel. The ability of the solid oxide fuel cell to perform reliably with different fuel types (H 2 , C n H m , CO) is one of the key requirements for its further commercialization.
Keywords: solid oxide fuel cell ; anode ; catalyst ; structure

Structure and Properties of Ceramics Based on Monetite and Nanodispersed Silica by O. Ye. Sych; N. D. Pinchuk; V. V. Pasichnyi; S. O. Ostapenko; A. V. Kotlyarchuk; G. B. Tovstonog; Ya. I. Yevich (175-182).
Calcium–phosphate ceramics based on monetite and nanosized silica are produced by sintering at 500°C. It is established that phase changes and solid-phase reactions occur during sintering to form ceramics that contain β-calcium pyrophosphate (Ca2P2O7), calcium silicate (wollastonite, CaSiO3), and insignificant amount of β-tricalcium phosphate (Ca3(PO4)2). It is shown that the addition of silica inhibits re-crystallization of calcium pyrophosphate into tricalcium phosphate, if compared with ceramics prepared from monetite with no silica added. It is established that increasing the silica content in the starting composition leads to a decrease in the minimum pore size from 0.83 to 0.21 μm. Highly pure nanosized silica (content of SiO2 > 99%) prepared by heat-treating of silicon carbide waste in a solar furnace is used in our research. The porosity of ceramics produced reaches 43.5–46.8% and the compressive strength is 16–24 MPa.
Keywords: monetite; silica; calcium pyrophosphate; tricalcium phosphate; sintering; ceramics

The paper studies the structurization of aluminum oxide ceramics sintered with additions of a synthesized fine SiC–Fe 2 O 3 powder alloy. The fine-grained powder alloy particles promote the densification of the alumina matrix. The mechanical properties of the composites are examined. The material obtained is tested as a cutting tool.
Keywords: solid solution of carbon in silicon carbide ; aluminum oxide ; iron oxide ; sintered iron ore concentrate ; stishovite ; cutting tool

Corrosion Resistance of Ultrahigh-Temperature Zirconium Boride Ceramics Under Concentrated Solar Radiation by T. V. Mosina; I. P. Neshpor; O. M. Grigoriev; A. D. Panasyuk; V. V. Pasichnyi; G. O. Frolov; O. V. Koroteev (189-193).
The behavior of ZrB2–MoSi2(SiC) and ZrB2–SiC–ZrSi2 ceramics under concentrated solar radiation is examined. The effect of zirconium silicide and molybdenum silicide admixtures on the formation of protective oxide layers on the ultrahigh-temperature ceramics in air at elevated temperatures is studied with the purpose of controlled development of dense protective films ensuring high service characteristics. The structure and composition of the oxidized materials are analyzed. The highest corrosion resistance is shown by the ZrB2–MoSi2 ceramics.
Keywords: concentrated solar radiation; ultrahigh-temperature ceramics; corrosion resistance

Thermodynamic Properties of Binary CE–IN Alloys by M. I. Ivanov; V. V. Berezutskii; M. O. Shevchenko; V. S. Sudavtsova (194-200).
The mixing enthalpies of liquid binary Ce–In alloys (0 < x In < 1) at 1500 K are determined by isoperibol calorimetry. The thermodynamic properties of the liquid Ce–In alloys are calculated for the entire composition range using the model of ideal associated solutions. The thermodynamic activities of melt components show negative deviations from the ideal behavior. The mixing enthalpies are characterized by significant exothermic effects. The minimum mixing enthalpies of the melts are –43.8 ± 0.2 kJ/mol at x In = 0.57.
Keywords: mixing enthalpy ; mixing entropy ; Ce–In alloy ; model of ideal associated solutions

The wetting of ZrO2 ceramics with Ag–Cu–O melts in air when electric current passes through th interface has been studied. Special samples were fabricated for experiments: parallel ZrO2 ceramic plates, with drops of copper–silver alloy being located between them. Direct current was induced on the plates after melting of the drops. It is found that the anode plate is wetted better at certain amperage. Microstructural analysis shows that much more copper oxide adsorbs on the anode plate than on the cathode. It is assumed that oxidized copper is reduced on the cathode and thus migrates to the anode, worsening the wetting of the cathode.
Keywords: wetting; electric current; interface; anode; cathode; ZrO2 ceramics

Effect of Electrode Material on the Electrical Properties of Tin Dioxide Thick Films by A. G. Gonchar; B. M. Rud’; N. I. Siman; E. Ya. Tel’nikov; A. A. Rogozinskaya; L. I. Fiyalka; A. K. Marchuk (204-209).
The influence of electrode materials made of Ag-containing paste and Ni3B-based paste on the properties of fine SnO2 thick films is studied. The Sn0.97Sb0.03O2 nanopowder is introduced into the thick-film composite to intensify film consolidation during heat treatment, enhance film adhesion to the substrate, and control the resistivity. X-ray diffraction and electron microscopy are applied. The dependences of film resistivity on composition of the conducting phase are established. The effect of heat treatment temperature on the resistivity and current-voltage characteristics of films on silver and nickel electrodes is examined. It is shown that the electrodes made of powdered Ni3B paste can be used for SnO2 films whose heat treatment temperature does not exceed 1073 K, in particular, for gas sensors.
Keywords: thick film ; electrodes ; tin dioxide ; resistivity ; nanopowder

Theoretical Strength of Borides and Quasibinary Boride Eutectics at High Temperatures by D. A. Zakaryan; V. V. Kartuzov; A. V. Khachatryan (210-214).
The theoretical strength of LaB6 and MeB2 borides and a eutectic LaB6–TiB2 system is calculated with quasiharmonic approximation for uniaxial strain in the temperature range between 0 and 2750 K. It is established that the linear temperature dependence of strength, typical of LaB6, does not hold in the range 1300–2200 K. It is shown that the theoretical strength increases with higher temperatures. The same dependence is typical of the LaB6–MeB2 systems (Me is Ti, Zr, Hf) at 0.7 mol.% LaB6.
Keywords: temperature dependences ; theoretical strength ; borides ; uniaxial deformation ; eutectic

It is established that SiC obtained through the carbidization of rice husk inevitably contains unreacted carbon, since the C/SiO2 ratio in the starting material is 36% higher than the stoichiometric one. Two methods are proposed for producing SiC without carbon impurities. One is to conduct additional oxidative annealing at 770°C, and the other is to introduce an additional amount of SiO2 with sodium silicate in the hydrothermal carbonization process.
Keywords: rice husk ; silicon carbide ; excess carbon ; hydrothermal treatment ; oxidative annealing

Phase-Structural and Electrochemical Properties of La2MgNi9 Alloys by Yu. V. Verbovitskii; R. V. Denis; V. V. Shtender; I. Yu. Zavalii (220-226).
Multiphase La 2 MgNi 9 alloys are synthesized by induction melting. The crystalline structures of all phases in the alloys are determined with X-ray diffraction. The La 2 MgNi 9 electrodes with nickel as a binder and electrical conductor are prepared and their charge–discharge characteristics are studied. The influence of homogenizing annealing and mechanical grinding on the discharge capacity and cyclic stability of the metal hydride (MH) electrodes is shown. The best electrochemical parameters are observed for powdered as-cast alloys.
Keywords: lanthanum ; magnesium ; nickel ; alloy ; mechanical grinding ; electrode materials ; Ni–MH batteries

The corrosion resistance of Cr 3 C 2 –15 % Ni (KKhNF15) alloy in solutions of acids, alkalis, and salts is studied. It is found that the corrosion rate of this alloy is one fifth to one thirtieth that of 40Cr13 (40Kh13) stainless steel, stellite, and WC–8 % Co (VK8) alloy used to manufacture valve pairs for oil well pumps. The production of balls from the sintered Cr 3 C 2 –15 % Ni (KKhNF15) alloy and of valve seats from the Cr 3 C 2 –28 % Ni (KKhNF28) alloy is examined. The modes of rough machining, finishing, and abrasive mechanical processing of chromium carbide hard alloys are optimized depending on the duration of processes and the particle size of B 4 C powder. The batches of valve pairs manufactured from chromium carbide alloys were tested in industrial conditions at enterprises of the Ukrnafta Oil and Gas Company. The service life of a valve assembly made of the corrosion-resistant hard alloys is more than two years, which is three to five times higher than the life of such parts made of conventional materials. The standards developed for ‘seat–ball’ valve pairs from chromium carbide alloys are indicated (TU U. 28.4–02126745–001–2002).
Keywords: chromium carbide ; nickel–phosphorus ; valve pair ; valve seat ; ball ; sphericity ; corrosion resistance ; service life

Metallographic Analysis and Microstructural Image Processing of Sandblasting Nozzles Produced by Powder Metallurgy Methods by O. Yu. Povstyanoi; V. A. Sychuk; A. McMillan; V. D. Rud’; O. V. Zabolotnyi (234-240).
The structure of sandblasting nozzles is subjected to morphological analysis. Metallographic analysis and full processing of microstructural images show that the studied samples can be used in practice. Modern application software is used to develop a technique for determining the structural and morphological parameters of the sample sandblasting nozzle. Further research of the nozzles, including statistical processing of the characteristics obtained, calculation of average structural sizes, and visualization of structural analysis, is planned.
Keywords: nozzle; sandblasting; metallographic analysis; microstructure

The paper overviews a historical evolution of the technology, knowledge, and application of various forms and allotropic modifications of carbon as a component and base for graphitized-carbon, vapor-phase, nanostructured, and composite materials and describes the development and implementation of the synthesis of high-pressure phases and diamond-based superhard materials. The chronology of the most important developments, discoveries, and applications of carbon and associated materials is presented.
Keywords: carbon; coal; coke; pyrolytic graphite; pyrolytic carbon; fullerene; fullerite; nanotubes; graphene; carbon composites; carbon fabric; high-modulus carbon fibers; synthetic diamond; detonation diamond; superhard materials; chronology of development and discoveries