Powder Metallurgy and Metal Ceramics (v.50, #5-6)

Methods for determining the rheological and crystallization properties of basalt melts are considered. The physical properties of basalt melts suitable for the production of continuous fibers are compared with those of E-glass melts. It is established that the shape of the melt stream characterizes the fiber-forming area and depends on the production parameters and melt properties. A mathematical model is proposed to describe heat exchange during slow flow of basalt melt through a short nozzle into air and during its cooling. The longitudinal temperature distribution in both the melt and nozzle wall is calculated for various structural and processing parameters. It is shown that the melt is cooled to the greatest extent at low flow velocities (high viscosity) in longer nozzles with large internal diameter (small wall thickness). The results may be used to calculate temperature of the melt in a free stream flowing out of a nozzle and to optimize the continuous basal fiber technology.
Keywords: basalt melt; nozzle; formation of fibers; simulation of heat-exchange processes

Processing and magnetic properties of iron powders clad with phosphorus and nickel–phosphorus by N. V. Boshitskaya; O. V. Vlasova; L. M. Apininskaya; T. M. Yarmola; I. V. Uvarova (256-261).
Composites based on iron powders clad with nickel and nickel–phosphorus are developed using modified methods such as thermochemical decomposition of diammonium phosphate, thermochemical synthesis in a vibrating layer, chemical phosphating, and reduction nickel salt with a sodium hypophosphite solution in both acid and alkaline media. The cladding of iron powders with phosphorus increases the magnetic flux density by 20% on average and permeability by 25% and promotes higher resistivity, thus decreasing magnetic losses. The coating partially remains on iron particles in composites based on powders clad with phosphorus in a vibrating layer or with nickel–phosphorus in acid media after high-temperature sintering. This decreases magnetic losses as well. Laboratory tests are performed to determine the corrosion resistance of iron powders before and after cladding using an accelerated drop analysis. It is established that phosphorus and nickel–phosphorus coatings increase the corrosion resistance by a factor of 2.5 to 3.0 apparently because protective phosphide layers form on iron particles. The materials based on iron powders clad with phosphorus and nickel–phosphorus differ from conventional ones in high magnetic properties, high corrosion resistance, and low magnetic losses at a frequency of 50 Hz and may be recommended for the manufacture of soft magnetic articles operating in both constant and alternating fields of power line frequency.
Keywords: soft magnetic materials; magnetic properties; clad powder; iron; nickel

Mathematical one- and two-parameter models used to describe the grinding of structural materials and ores are analyzed with the purpose of their potential application to describe the grinding of metal powders. Experimental verification is carried out on PZhR-3 iron powders (as per GOST 9849–88) and ShKh15 steel powders resulting from the disposal of bearing-production waste. The grinding of metal powders is most accurately described (with the lowest difference between theoretical and experimental results) with Razumov’s kinetic equation.
Keywords: sludge; metal powder; rolling; grinding

Effect of ball milling on formation of ZnAl2O4 by reduction reaction of ZnO and Al powder mixture by A. Hedayati; Z. Golestan; Kh. Ranjbar; G. H. Borhani (268-274).
It is well known that thermal energy generated during high energy milling / alloying can facilitate the reduction reaction, leading to formation of compounds and oxide reinforced composites. Solid state reduction reaction by the mixture of high purity fine zinc oxide and metallic Al powders is investigated. The ZnO powders are added to aluminum powder in ball milled and milled conditions, and then attrition milled for different times. The former is called double ball milled, and the latter is called single ball milled since it is only attrition milled. The results are further studied and verified by XRD, SEM, DTA and particle size analyzer. The complete reduction of ZnO to Zn is almost obtained in powders double ball milled for 10 h, which is converted to ZnAl2O4 when vacuum annealed. In the case of single ball milled powder, reduction of ZnO is partially done and no ZnAl2O4 phase forms after annealing.
Keywords: powders; ball milling; reduction reaction; attrition milling; zinc oxide; aluminum; ZnAl2O4

Selective laser sintering/melting of nitinol–hydroxyapatite composite for medical applications by I. V. Shishkovskii; I. A. Yadroitsev; I. Yu. Smurov (275-283).
The layer-by-layer synthesis of 3D parts from nitinol (NiTi intermetallide) and hydroxyapatite additions using selective laser sintering/melting (SLS/SLM) is studied. The effect of different laser parameters on the structure and phase composition of sintered/melted samples is analyzed with optical and scanning electron microscopy, x-ray diffraction, and energy-dispersive x-ray analysis. Optimum SLS/SLM parameters are determined for the synthesis of NiTi + HA to be used in tissue engineering and manufacture of medical devices (pins, nails, porous implants, drug delivery systems). No significant destruction of HA ceramics under laser treatment is observed. The amount of nickel released to the surface of 3D parts decreases owing to the additional oxidation of free titanium during SLS/SLM and the formation of a protective HA layer. Full-density 3D parts are produced from nitinol by SLM including preheating to 300°C.
Keywords: selective laser sintering/melting (SLS/SLM); porous tissue engineering; nitinol; hydroxyapatite (HA)

Titanium oxide vacuum condensates are produced by laser evaporation in vacuum, which involves vapor condensation onto a polycrystalline molybdenum substrate heated between 200 and 1500°C. The phases formed in titanium oxide vacuum condensates and their microstructure are studied with x-ray and electron diffraction and transmission electron microscopy. It is established that the phases formed in titanium oxide vacuum condensates are determined by substrate temperature (T s): amorphous TiO2 forms at T s < 400°C, anatase crystallizes at higher T s and coexists with rutile at T s = 700–900°C, and rutile alone is observed at T s > 900°C. Laser evaporation at T s < 1400°C promotes oxygen-rich TiO2 phases and that at T s ≥ 1400°C leads to Magnéli phases in titanium oxide vacuum condensates. Higher T s results in phases in which the titanium–oxygen atomic ratio does not correspond to the TiO2 formula. It is shown that variation in the substrate temperature and the size of crystallites in titanium oxide vacuum condensates is symbate.
Keywords: vacuum condensates; titanium oxide; Magnéli phases

Effect of chromium and manganese nitrides on the structure and properties of Kh18N15 powder stainless steel by V. A. Maslyuk; G. G. Lvova; V. Ya. Kurovskii; A. A. Mamonova (289-294).
The paper examines the doping of Kh18N15 powder stainless steel with chromium and manganese nitrides. It is established that the base of stainless steel–10% chromium nitride material is additionally doped with chromium and nitrogen during its structurization. If steel is doped with manganese nitride, complex chromium–manganese nitride forms after quenching at 950°C. One part of the nitride reacts with the base material and the other is evaporated. To prevent nitrogen losses, stainless steel compacts must be subjected to combined nitriding, in which one part of nitrogen is added as chromium and manganese nitride powders and the other is introduced during thermal treatment of the material in nitrogen-containing environments.
Keywords: internal nitriding; chromium nitride; manganese nitride; hot-forged materials

Protective properties of composite oxide coatings deposited by sol-gel method by S. Miszczak; B. Pietrzyk; Z. Gawronski (295-300).
In this work, we compare the protective properties, morphology, and adhesion of unary and composite, sandwich Al2O3–TiO2 coatings deposited on X5CrNi18-9 austenitic stainless steel using the sol-gel method. It is found that the type and sequence of the films in investigated composite sandwich coatings have essential influence on their properties. The best protective properties exhibit coatings in which Al2O3 film is directly on the substrate surface. The best adhesion is revealed in coatings in which TiO2 film is directly on the steel surface. It is found that composite oxide sol-gel coatings improve the resistance of stainless steel better then unary coatings both in the range of electrochemical and high-temperature corrosion. This improvement can result from mutual influence of titania and alumina films by delay of their crystallization process.
Keywords: austenitic stainless steel; protective sandwich coatings; sol-gel method; titanium oxide; alumina; electrochemical and high-temperature corrosion

A continuum model based on the physical hypotheses of the discrete contact model is developed to describe the elastic and plastic properties of isotropic powder materials, taking into account the inhomogeneous deformation of the solid phase. The localization of elastic and plastic deformation is described by hypothesizing that deformable and nondeformable volumes form in the solid phase and that the resistance to deformation is associated only with the deformable volume. An analytical dependence of the deformable volume on the density of powder material is provided. The proposed model ensures high-accuracy fit to the experimental compaction curves at the stages of interparticle slip and plastic deformation of particles. At the beginning of plastic deformation, a particle is regarded as a cast one already plastically deformed and hardened to the level of the effective yield strength of the solid phase. The particle is further hardened as a cold-worked cast material is. Good agreement is reached between calculated and experimental data on the elastic moduli and plastic compaction of powders during isostatic pressing and deposition in a high-pressure chamber.
Keywords: powder material; deformable volume; elastic moduli; plasticity condition; strain hardening

Composite WC–35% Ni produced from ultrafine WC + NiO powders. I. Density and structure by A. I. Tolochin; A. V. Laptev; I. Yu. Okun; M. S. Kovalchenko (313-321).
The density and structure of an ultrafine-grained WC–35 wt.% Ni composite produced by short-term solid-phase compaction at different temperatures and about 1200 MPa are examined. The starting powder mixture consists of tungsten carbide and nickel oxide, but one part of the mixture is reduced in hydrogen and the other is mixed with saccharose to reduce nickel from its oxide during heating of green briquettes. In the latter case, it takes one stage to synthesize the metal phase and consolidate the WC–Ni mixture. It is established that the composite samples produced from the powder mixture containing saccharose show more intensive shrinkage during heating than the samples produced from the mixture preliminary treated with hydrogen. High pressure promotes practically porousless samples above 1150°C. It is shown that the composite produced from the carbide–oxide mixture by the reduction of saccharose carbon has finer grains and differs in more uniform distribution of tungsten carbide in the nickel matrix.
Keywords: composite; hard alloy; density; structure; resistivity; reduction; tungsten carbide

Effect of abrasive particle sizes on abrasive wear of ceramic coatings sprayed by plasma process by M. S. Gok; O. Gencel; V. Koc; Y. Kuchuk; V. V. Cay (322-330).
This study examines the effects of abrasive grain size on abrasive wear behaviors on surfaces coated with different types of ceramics. To this end, the surface of AISI 1040 steel is coated with the ceramic materials of 5% SiO2–3% TiO2–92% Cr2O3, 60% Al2O3–40% TiO2, pure Al2O3 and 87% Al2O3–13% TiO2 using the plasma method. Following the coating process, the abrasive wear resistance of each sample is tested by the ring-on-disc method. 80–220 mesh SiC abrasive paper is used as abrasive. The best wear resistance is obtained with the ceramic coating containing 92% Cr2O3, which is followed by pure Al2O3 and 87% Al2O3–13% TiO2, respectively. The lowest wear resistance is observed in 60% Al2O3–40% TiO2 ceramic coating. Wear resistance of the samples increases with increasing hardness value and decreasing abrasive grain size. It is observed that wear mechanisms occurring on the samples’ wear surfaces change with changing abrasive grain size. Wear mechanisms such as microscratching, microcracking, and plastic deformation are observed in the samples.
Keywords: coating; abrasive wear; ceramics; plasma spray

Tribotechnical characteristics of superhard boron nitride materials in contact with hard alloys by Yu. V. Naidich; A. G. Kostornov; A. A. Adamovskii; V. T. Varchenko; A. D. Kostenko (331-337).
The paper examines the tribotechnical characteristics of samples produced from superhard boron nitride materials in friction contact with hard alloys of VK and TK grade without lubrication. All friction pairs possess high wear resistance. The hard alloys show three to six times higher wear than that of boron nitride materials in all friction pairs with different combinations of materials. The maximum wear resistance is exhibited by composite 10–hard alloy friction pair. With higher sliding velocity, the friction coefficient of all pairs decreases and temperature in the friction area increases. The maximum temperature in the friction area at which the materials can perform for a long time is 300°C.
Keywords: superhard materials; sample; solder; friction unit; surface; roughness; contact area; tribotechnical characteristics

Low-temperature sintering of yttria-stabilized zirconia produced from amorphous powders by S. V. Gabelkov; R. V. Tarasov; N. S. Poltavtsev; A. P. Kryshtal; A. V. Pilipenko; A. G. Mironova (338-344).
Low-temperature sintering of a tetragonal zirconia solid solution proceeds through the fracture of all agglomerates during pressing of samples from hydroxide powder coprecipitated from an aqueous solution and through the increased reactivity of amorphous zirconium hydroxide and oxide. Thermal treatment at 1100°C for 1 h produces ceramics with relative density 0.928, grain size 120–135 nm, and pore size 50–75 nm. Sintering is most intensive in the temperature range 950–1150°C and is less active in the range 800–950°C.
Keywords: agglomerate; aggregate; powder; amorphous hydroxide; coprecipitation from aqueous solutions; amorphous zirconia; sintering; pressing

The Al2O3–HfO2–La2O3 phase diagram. II. phase equilibria at 1250 and 1600°C by S. M. Lakiza; Ya. S. Tishchenko; V. P. Red’ko; L. M. Lopato (345-349).
The isothermal sections at 1250 and 1600°C for the Al2O3–HfO2–La2O3 phase diagram are constructed for the first time. No ternary compounds or appreciable regions of solid solutions based on components or binary compounds are found in the ternary system. The triangulation of the system is determined by the La2Hf2O7 phase being most thermodynamically stable.
Keywords: ceramics; hafnia; alumina; lanthana; isothermal section; phase diagram

The Gibbs energy, enthalpy, and entropy of formation of erbium monobismuthide from solid erbium and liquid bismuth are determined by measuring electromotive forces in the temperature range 803–1093 K. The melting enthalpy and entropy of pure bismuth are used to calculate the thermodynamic properties of formation of erbium monobismuthide from solid components. The results are compared with the relevant published data. The interaction of erbium with p-elements of group 5 and period 5 of the Periodic Table are discussed. The energy of interatomic interaction of erbium with p-elements of group 5 decreases with greater atomic numbers of p-elements, while the energy of interatomic interaction with p-elements of period 5 increases with a greater electronegativity difference of the components.
Keywords: thermodynamic properties; Gibbs energy of formation; enthalpy of formation; entropy of formation; erbium monobismuthide

Interaction of dental and maxillofacial keradent-1 alloy with oral cavity electrolyte by V. O. Lavrenko; V. M. Talash; V. V. Los; V. V. Lashneva; L. I. Kuznetsova (356-361).
The methods of potentiodynamic polarization curves and quantitative Auger electron spectroscopy are used to establish the formation of a protective multilayer film in the interaction of dental and maxillofacial Keradent-1 alloy with the oral cavity electrolyte (3% NaCl solution). It is shown that the first (inner) part of the protective film (30 nm thick) represents a solid solution of oxygen in the metals of the alloy and the outer part of the film consists of three layers: CoO oxide (5 nm thick) at the boundary with the solid solution of oxygen, a mixture of CrO and CoO oxides (3 nm thick) in the middle, and Cr2CoO4 spinel (2 nm thick) in the outer sublayer. The experiment and calculations using the Faraday law show the number of Cr3+, Co2+, and Ni2+ ions that pass into the solution during electrolysis. These numbers are almost one three-hundredth of the admissible concentrations of these metals in the oral cavity.
Keywords: Keradent-1 alloy; anodic polarization; interaction with oral cavity electrolyte; composition of protective film

Structural types of boron nitride particles produced by carbothermal synthesis by G. S. Oleinik; V. I. Lyashenko; É. V. Prilutskii; A. V. Kotko; V. M. Vereshchaka (362-372).
Transmission electron microscopy and microdiffraction are used to examine boron nitride produced by carbothermal synthesis (using saccharose as a carbon-containing component) in the temperature range 1000–1450°C in nitrogen. It is established that onion-like particles form during structural ordering of turbostratic boron nitride in the range 900 − 1000°C. The structural types of BN particles are classified according to: 1) crystal morphological features (onion-like particles, cylindrical and faceted tubes, and lamellas), 2) formation mechanisms (structures of growth formed through nucleation and structures of breakdown formed through structural transitions), and 3) synthesis temperatures. The tubes grow from the gas phase and their crystal morphological forms differ in phase composition (cylindrical tubes consist of the hexagonal BN phase and faceted tubes of the rhombohedral one). At T ≥ 1350°C, rhombohedral–hexagonal phase transition and transformation into multilayered polytypes occur in faceted tubes due to a highly anisotropic thermal expansion coefficient of graphite-like modifications of boron nitride.
Keywords: boron nitride; particles; substructure; onion-like particles; tubes; faceting

Effect of electrode porosity on the electrospark deposition of recovery coatings by S. M. Kirilenko; O. V. Paustovskii; M. V. Karpets (373-375).
The paper examines how the porosity of electrode materials used to restore parts influences the electrospark deposition process. A higher porosity decreases the heat conductivity of the electrode material. A smaller amount of heat spreads along the electrode and, hence, a greater amount of heat remains for melting. Erosion and deposition of the material increase accordingly.
Keywords: spark-deposited coating; porosity; heat conductivity; erosion; deposition