Structure and high-temperature strength of composite materials based on boron nitride

The structure and physicomechanical properties of composite materials based on boron nitride within which new phases (mullite and sialon) form during hot compaction are studied. It is established that the microstructure of composites is specified by their texture formation caused by the crystal morphology of boron nitride particles and it is almost independent of composite phase composition. It is shown that the main factor that affects strength is porosity. The dependence of strength on porosity is exponential in character. The strength of boron nitride-mullite and boron nitride-sialon composites is 110–140 MPa and at 20–1200°C it is almost unchanged. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(449), pp. 33–39, May–June, 2006.     

Riction properties of composite materials of the system TiN - Ain. II. Effect of oxide films on friction and wear of a ceramic material — Steel system

Friction and wear are studied for materials of the system TiN — AlN preliminary oxidized at 800–1100°C. It was established that thin oxide films containing Al₂TiO₅ and α-Al₂O₃, that promote a decrease in frictional wear, form on the surface of composite materials of the system TiN — AlN. Our assumptions are confirmed that the improvement in tribological properties of TiN — AlN composites is caused by forming oxide screening layers that prevent direct contact between the ceramics and steel counter-body. At high rates (V=16 m/sec) and pressure (P=2.0 MPa) the oxide films form more rapidly. Translated from Poroshkovaya Metallurgiya, Nos. 1–2(411), pp. 121–124, January–February, 2000.     

Effect of factors governing dry friction on structure formation for the tribological synthesis zone in composites based on copper

Features and peculiarities of structure formation for the friction zone in highly effective composite materials based on copper for prescribed experimental conditions (high contact loads and sliding rates, absence of a lubricant, operation in a high vacuum or in air) are considered. It is shown that reliable efficiency for a tribological system under friction conditions with action of high compressive forces and sliding rates is provided by material adaptation that is achieved via the tribological synthesis at the contact surfaces of a lubricating layer different in composition and structure from the original composite. __________ Translated from Poroshkovaya Metallurgiya, Nos. 3–4(448), pp. 14–21, March–April, 2006.     

Tribological Properties of Composite Materials Based on Refractory Titanium Compounds

The tribological properties have been examined for composite materials based on binary titanium-chromium boride and titanium nitride under conditions of dry friction over a wide speed range (1–25 m/sec). The materials have good tribological properties, which exceed by almost an order of magnitude those of known materials. Specifications are formulated for materials promising for high-speed friction units. A necessary condition for viability in high-speed friction units is high strength of the adhesion between the films of oxidation products, and another is low tendency for adhesion with the counterbody. __________ Translated from Poroshkovaya Metallurgiya, Nos. 7–8(444), pp. 58–64, July–August, 2005.     

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

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. __________ Translated from Poroshkovaya Metallurgiya, Vol. 47, No. 1–2 (459), pp. 151–161, 2008.     

Sintered ceramics based on boron nitride and carbide

The formation of BN-B₄C composite materials by sintering in nitrogen is investigated. Structural, mechanical, and chemical characteristics of these materials are examined. Excellent dielectric properties, thermal and chemical stability, and erosion resistance in high-intensity laser beams enable high-temperature application of BN-B₄C composite materials. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 1–2(453), pp. 58–63, 2007.     

Behavior of multilayer steel-bronze composites on frictional loading

Tribological aspects are examined for layered composites made by consolidation. Dry friction tests at sliding speeds of 1.6–4.3 m/sec show that this multilayer antifriction material is better by 1–2 orders of magnitude in wear resistance than the initial material. The multilayer composite can withstand a load increased by an order of magnitude without losing its viability under the conditions of surface-structure adaptation. Deceased. Translated from Poroshkovaya Metallurgiya, Nos, 1–2(411), pp. 38–44, January–February, 2000.     

Reaction of boron-containing materials with titanium during self-propagating high-temperature synthesis

We have studied the contact reaction of titanium, chromium, and tungsten borides with titanium. We have established that the materials react according to an exothermic solid-phase reaction mechanism with formation of titanium monoboride and diboride. The reaction is limited by diffusion of boron atoms through the layer of titanium monoboride formed. This makes it possible to successfully use reaction to effectively control the process for obtaining composite materials in the Ti-B₄C system under selfpropagating high-temperature synthesis conditions. __________ Translated from Poroshkovaya Metallurgiya, Nos. 3–4(448), pp. 67–72, March–April, 2006.     

Carboborosilicide and oxide composite coatings on carbon materials

Complex carboborosilicide and oxide coatings on carbon materials prepared by vacuum activated diffusion impregnation predominantly through a liquid phase, vacuum fusion, and enamelling are studied. It is established that coating formation from the vapor phase hardly reduces the original porosity of carbon materials. The complex protective coatings developed that are formed by vacuum activated diffusion impregnation through a liquid phase lead to a reduction in the original porosity and gas permeability of carbon materials thereby increasing their high-temperature strength and heat resistance at elevated temperatures. It is shown that higher heat resistance in the temperature range 1800–2000 °C is provided by multilayer coatings based on carbides and borides of silicon, titanium and zirconium, borosilicides of tungsten, hafnium, molybdenum, and also oxides of silicon, aluminum, zirconium, and hafnium. It is established that the protective properties of coatings depend markedly both on their composition, structure, preparation method and on the form of the original carbon materials. __________ Translated from Poroshkovaya Metallurgiya, Nos. 3–4(448), pp. 21–27, March–April, 2006.     

Effects of a solid lubricant and technological parameters on the friction, wear, and mechanical properties of a composite based on polytetrafluoroethylene powder

Mathematical experiment planning methods have been applied to the effects of solid molybdenum disulfide lubricant content and those of technological parameters (content of special carbon fiber, preliminary size reduction time, and composite mixing time) on the antifriction and other mechanical properties of composite materials based on polytetrafluoroethylene and carbon fiber. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(449), pp. 21–32, May–June, 2006.     

Effects of preparation technique for MK-5 material on frictional and wear response

A study has been made on how the method of making a tribotechnical material affects the frictional and wear behavior. The materials have been made from identical initial powders, which corresponded in composition to standard MK-5 powder material, but different methods were used: traditional sintering under pressure and plasma spraying. The tribological properties of material made by plasma spraying are better than those of ones made by the traditional method, because of the presence of oxides formed during the spraying. Translated from Poroshkovaya Metallurgiya, Nos. 1–2(411), pp. 44–47, January–February, 2000.     

Promising trends in the development of methods of fabricating structural powder materials (survey)

In the new millennium a trend focused on making improvements in existing technologies of powder metallurgy and on the development of new and promising trends in the creation of powder structural materials is observed. The development of the technology of powder metallurgy is intended to improve methods of warm and injection molding, laser and mechanical alloying, and nitration of high-and lowalloy steels. Considerable attention has been paid to the production of structural materials made of intermetallic compounds, materials, the properties of which exhibit functional gradients. There has also been emphasis on creating nanomaterials fabricated by the sol-gel method, mechanical alloying, and powder spraying. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(449), pp. 92–100, May–June, 2006.     

Vibrodeformation properties of construction, composite, and high-porosity sintered materials

The indices of ultimate cyclic strain ε₋₁ and vibrodeformability R_ε (as the product of ε₋₁ and the decrement of material vibrations at this level of deformation) are introduced. Data on the fatigue strength and vibration decrement of traditional structural materials based on titanium, aluminum, magnesium, iron, and copper, as well as composite condensed materials of microlaminate and dispersion-strengthened structure and sintered high-porous materials based on copper powders, fibers, and foamed copper are analyzed. This allowed us to establish advantages of sintered high-porous materials in comparison with compact ones, and to conclude that high-porous materials based on discrete fibers, and foamed metals based on traditional structural materials will have higher ε₋₁ and R_ε indices than those of compact matrices. As far as the index of vibrostrength R_σ is concerned, sintered high-porous materials will be inferior to the compact materials. __________ Translated from Poroshkovaya Metallurgiya, Nos. 7–8(450), pp. 87–98, July–August, 2006.     

New technologies in powder metallurgy and ceramics developed in Belarus. A survey

Basic trends in scientific and technical activity, new technologies in powder metallurgy, and new materials created at the Institute of Powder Metallurgy of the National Academy of Sciences of Belarus since the early 1990s through the present day are considered. The article reviews the contribution of Belarus scientists to the development of sintered functional materials and anti-friction composite materials, the development of technologies of drop forging of sintered billets, infiltration of powder compacts, warm pressing of powders and additional pressing of compacts, in the creation of porous powdered materials with anisotropic structure, porous-capillary materials, and industrial ceramic, in the use of technologies of powder metallurgy to fabricate diamond tools, and create materials and technologies of thermal deposition of coatings from powders. __________ Translated from Poroshkovaya Metallurgiya, Nos. 1–2(447), 118–128, January–February, 2006.     

Manufacturing porous materials from metalorganic mixtures: Report 2

The morphology of the surface and fracture of highly porous materials obtained during the thermal destruction of metalorganic mixtures (MOM) was investigated. The size and shape of pore channels in the finished product were shown to be determined through the fractional composition and the particle shape in MOMs. The effect of the porosity on the permeability and strength of sintered materials was considered. The permeability was demonstrated to depend not only on the value, but also on the shape of pore channels. Combining the techniques of powder metallurgy with chemical-metallurgical processes allows us to obtain materials with a porosity of 70–80% and a strength of no less than 5–25 MPa. If the pore size was from 10 to 100 μm, the permeability of materials was (in 10⁻¹² m²) 1–3 for Mo, 0.5–6 for Mo-Ni, and 2–6 for Ti-Mo.     

Effect of Surface Treatment with Concentrated Energy Fluxes on the Properties of Composite Materials Based on Silicon Carbide and Coatings Made from Such Composites

Based on a study of the structure and composition of the composite ceramic SiC - Al₂O₃ - ZrO₂, its tribomechanical properties and behavior in high-temperature corrosion, we recommend the material for use as sealing elements and for deposition of wear-resistant and corrosion-resistant coatings. We have studied the formation of gradient layers when the ceramic surface is modified with refractory titanium compounds TiN - TiB₂ (1:1) with an Fe(Ni) - Cr - Al undercoat using concentrated solar radiation and when the steel surface is modified with laser irradiation of the SiC - Al₂O₃ - ZrO₂ coats. We have shown that laser modification of steel by the silicon carbide-based composite increases its corrosion resistance by a factor of 4–5 at 800–900 °C. __________ Translated from Poroshkovaya Metallurgiya, Nos. 7–8(444), pp. 91–99, July–August, 2005.     

Production of manganese magnesia sinter using enriched nikopol manganese ore and magnesia-silicate slag from ferronickel production

The industrial introduction of a new production technology for manganese magnesia sinter (7–10% MgO) at PAO NZF is considered. In this technology, the raw materials are enriched Nikopol manganese ore and magnesia-silicate slag (28–30% MgO, 50–52% SiO₂) from the production of ferronickel (15–20% Ni) at Pobuzhsk Ferronickel Works on the basis of imported nickel ore with magnesia-bearing barren rock. Data are presented regarding the microstructure of the sinter, the chemical composition of the phase-mineral aggregations in the sinter, and the mechanical properties of standard and experimental sinter samples.     

Influence of the precrystallization flow of copper and aluminum melts on the mechanical properties of ingots

The influence of the precrystallization flow of copper and aluminum melts on the hardness and abradability of ingots is investigated. The flow was organized via passing the melts through the round-section tubes. The hardness of metals was determined by the Brinell method, and abradability was evaluated on a setup for investigating the friction properties of materials. The stability of the chemical composition of metals was monitored by spectral chemical analysis. It is established that there is an 8–17 and 7–10% increase in hardness and a 11–15 and 10–11% decrease in abradability, respectively, in the samples of copper and aluminum subjected to the flow in the molten state. It is noted that, taking into account the results of a spectral chemical analysis, the variation in the properties of metals is most likely caused primarily by the directed precrystallization flow of corresponding melts rather than by variations in the chemical composition.     

Stainless-steel porous-layered and framework fiber-powder composites

Porous layered and framework composites have been made from stainless-steel fibers and powders in the form of sheets. Measurements have been made on the electrical conductivity, elastic modulus, and ultrasound speed as dependent on the porosity, fiber and powder dispersions, and the structural features of the composites. Framework composites are better than layered ones throughout the porosity range, while purely fiber materials are better with porosity less than 60%. __________ Translated from Poroshkovaya Metallurgiya, Nos. 1–2(447), pp. 45–50, January–February, 2006.     

High-temperature oxidation of composite AlN-ZrB2-ZrSi2 ceramics

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. __________ Translated from Poroshkovaya Metallurgiya, Vol. 47, No. 1–2 (459), pp. 196–203, 2008.