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.     

Finely dispersed Si3N4−SiC powders and materials based on them

The objectives of the present research were to investigate the preparation of homogeneous ultrafine composite Si₃N₄−SiC powders by a plasmochemical process and the properties of ceramics produced from them. The chemical and phase compositions of the powders depended on the particle size of the initial powder, silicon input rate, and ratio of ammonium and hydrocarbon flow rates. The particle size and specific surface area of the compounds depended on the concentration of particles in the gas jet, and the cooling rate of the products. Composite powders containing from a few up to 90 mass % SiC, with specific surface areas of 24–80 m²/g and free silicon and carbon content less than 0.5 mass % were obtained. The main phases present were α-Si₃N₄, β-Si₃N₄, β-SiC, and X-ray amorphous Si₃N₄. Dense materials were prepared both by hot pressing at 1800°C under a load of 30 MPa and gas-pressure sintering at 1600–1900°C under a pressure of 0.5 MPa nitrogen. The plasmochemical composites had smaller pore sizes, were finer grained, and densified more rapidly than materials sintered from commercial powders. Institute of Inorganic Chemistry, Latvian Academy of Sciences, Salaspils. Translated from Poroshkovaya Metallurgiya, Nos. 1–2(405), pp. 7–12, January–February, 1999.     

Temperature effect on bending strength of hot-pressed boron carbide materials

The paper examines three groups of samples based on B₄C and B₁₃C₂ powders (with additions of Al and Al₂O₃ in the amount of 2 and 5 wt.%, respectively). It is established that the maximal strength (445 MPa) is characteristic of the material B₁₃C₂ over the whole temperature range. It does not change up to 1600°C. The increase in strength of B₄C-based samples is revealed over the range of 1200 to 1600°C, mainly for high-porous materials (10–12%). Presumably, this is due to the higher relaxation properties of porous material microstructure. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 5–6 (455), pp. 60–68, 2007.     

Adsorption-chemical activity and interaction in the boron nitride-titanium hydride system

The paper examines the effect of physicochemical properties of starting boron nitride and titanium hydride on their reactive activity in the synthesis of the TiN-TiB_x composite. There are kinetic data on thermal desorption of the active adsorbate from the BN surface, which precipitated from the gas mixture (20 vol.% O₂-80 vol.% N₂ under the relative humidity of 80%). Kinetics of hydrogen release from titanium hydride in isothermal conditions and controlled rate of temperature increase in the reactive system is researched. A possible mechanism of chemical transformations of starting compounds and synthesis of the TiN-TiB_x composite is considered. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 5–6 (455), pp. 102–110, 2007.     

Synthesis and physicomechanical properties of B4C-VB2 composites

We have studied the properties of composites in the B₄C-VB₂-C system, obtained by reaction synthesis with hot pressing. We have established that the presence of free carbon and vanadium boride in the ceramic makes it possible to activate the sintering process and to obtain a dense, highly dispersed ceramic with good structural homogeneity parameters for lower isothermal holding temperatures. The composite ceramic has higher hardness and bending strength over a broad range of vanadium boride content than the monophase ceramic based on boron carbide. The strength properties of the composite ceramic containing up to 8 vol.% vanadium boride are improved by means of a mechanism involving propagating cracks bending around obstacles. When the VB₂ concentration increases further, the properties of the composite are determined by a microcracking mechanism. In this case, we observe relatively small changes in the elastic characteristics, which depend linearly on the composition of the ceramic. Introducing vanadium boride into the material is also accompanied by an increase in the contact and microstructural strengths. The results obtained indicate that the new composite material is promising for fabricating wear-resistant and shock-resistant components of various structures and machines. __________ Translated from Poroshkovaya Metallurgiya, Nos. 1–2(447), pp. 59–72, January–February, 2006.     

Synthesis, heat resistance, and optical properties of boron silicide and materials based on it

Conditions of synthesis from elements of pure superfine powder of boron silicide B₄Si are investigated. It is shown that the silicide phase forms on boron particles and B₄Si particles inherit the shape and size of initial boron particles, which makes it possible to control the particle size of the powder obtained. The oxidation of pure boron silicide and materials based on it in air and their optical properties are studied. It is shown that chromium diboride added to boron silicide increases the oxidation resistance of B₄Si and hardly decreases its absorbance. The B₄Si-CrB₂ material can be successfully introduced into the compositions of heat-protective coatings operating in air at 1300 °C. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 3–4 (454), pp. 45–52, 2007.     

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.     

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.     

Contribution of electrospark alloying to the oxidation resistance of hard tungsten alloys

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. __________ Translated from Poroshkovaya Metallurgiya, Vol. 47, No. 1–2 (459), pp. 145–150, 2008.     

Synthesis and Characterization of Al–Mg–SiO<Subscript>2</Subscript> Particulate Composite Using Amorphous SiO<Subscript>2</Subscript> from Rice Husk Ash

This paper discusses the effect of the dispersion of amorphous nano size (35–55 nm) SiO₂ particles in Al–Mg (5%) alloy. Amorphous SiO₂ (>95% SiO₂) extracted from rice husk was added to the Al–Mg (5%) alloy in the proportion of 5 wt% of the Al–Mg alloy. The work aims to study the evolution of different phases like MgAl₂O₄, Mg₂Si, and MgO in Al–Mg–SiO₂ composite using amorphous nano SiO₂. Experimental results of the synthesized composite show presence of MgAl₂O₄ (Spinel structure) and other phases like MgO and Mg₂Si which impart hardness of 126.82 HV_10g to the composite. The Al–Mg (5%) SiO₂ composite microstructure appeared as a typical lamellar structure. The XRD and energy dispersive spectroscopy analysis display the presence of Mg₂Si formed along the grain boundary.     

Influence of the Composition and Structure of B4C - Al2O3 Ceramic on the Tribotechnical Characteristics in Friction Against Steel

The morphology and phase composition of friction surfaces and the tribotechnical properties of the (B₄C - Al₂O₃)-steel 45 system are studied under dry friction at various sliding velocities and contact loads. We have found that fine-grained secondary structures are formed on the friction surfaces. The morphology and phase composition of these structures depend on the ceramic composition and on the test conditions. A comprehensive investigation of friction surfaces, using x-ray, electron-diffraction electron-probe, and electron-microscopy analysis, has shown that the structure and morphology of the secondary phases determine the tribotechnical properties of ceramic-steel couples. The maximum wear resistance of B₄C ceramics containing 5-20 mass% Al₂O₃ is determined by the formation of dense secondary-phase thin films on the friction surface. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(443), pp. 49–59, May–June, 2005.     

Fatigue and Compression Characteristics of Al 6061–B 4 c Composite Materials

Aluminum matrix composites reinforced with boron carbide are a kind of materials that are widely used because of high strength, low density, and improved tribological properties. In this study, mechanical properties of Al 6061–B4C composites reinforced with B4C of three different particle sizes were investigated. In the Al 6061–B4C composite materials, produced by the powder metallurgy methods (extrusion of billets obtained by sintering at temperature of 550°C under pressure of 450 MPa), the change of mechanical properties such as hardness, compressive strength, and fatigue life, related to B4C particle size and the applied heat treatment mode (aging at 180°C for 5 h), were investigated. The hardness of the materials is increased with B4C grain size and the heat treatment. After the heat treatment, the fatigue life of Al 6061–B4C (3 μm) material increases slightly, while that of the composite materials decreases with larger size of B4C reinforcement. The fatigue life of the composite materials reinforced with a larger grain size B4C is reduced by heat treatment. While the compression test data of untreated composite materials were similar to each other, the heat treatment increased these values in all samples. The highest increase in the compression strength was observed in the composite reinforced with 17 μm sized B4C. The addition of graphite reduces the deformation ability of the composites.     

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.     

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.     

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.     

Technical study for fabrication of new cermet used as inert anode in aluminum molten-salt electrolysis

In aluminum electrolysis industry, traditional carbon electrodes have many disadvantages under molten-salt corrosive conditions (970°C), such as large quantities of CO₂ production and quick consumption of carbon. The best way is cermet, which is a kind of graded composite material and consists of spinel NiFe₂O₄ as a ceramic phase and Ni-Fe-X alloy as a metal phase. The fabrication of NiFe₂O₄ powder is studied by chemical co-precipitation method with different co-precipitation chemicals (NH₃· H₂O, NaOH); differential thermal analysis and thermal gravity (TG) test have also been carried out to evaluate the performance of fabricated powder. The fabrication of Ni-Fe-X alloy is studied with three different kinds of powder compositions (NiFeAlCuZn, NiFeAlCuSn, and NiFe), different forming methods and sinter conditions are also compared and discussed in detail. DTA, XRD, density, hardness and anti-oxidation tests are carried out to test the performance of fabricated materials. Finally, fabrication technical condition of cermet is studied and determined according to graded composite slurry casting method, which combines the ceramic phase and metal phase with good performance. The fabrication technique presented in this study is valuable for making new anti-corrosion electrode material used in aluminum electrolysis. Published in Poroshkovaya Metallurgiya, Vol. 46, No. 3–4 (454), pp. 52–61, 2007.     

Composite material based on nanocrystalline SiC reinforced with continuous SiC fibers

A paste of nanocrystalline particles was obtained by magnetron sputtering of a target consisting of silicon and graphite powders. The target and a silico-organic oil were evaporated together. Model specimens were fabricated from the paste and continuous SiC fibers. Interaction between the fibers and nanoparticles was investigated by measuring the internal friction of the model composite materials. It was found that sintering occurs in 16–20 h at 1473–1500 K for pastes containing nanoparticles with a diameter of =2–4 nm, and in 60–100 h for pastes with diameter =6–10 nm. The sinterng temperature is 230–270 K below the degradation temperature of the fibers. It was shown that it is possible to manufacture a composite material consisting of a nanocrystalline SiC matric reinforced with continuous SiC fibers. The bend strength of the composite was σ _B = (73 ± 9)·10⁷ Pat at 1500 K, and (64±12)·10⁷ Pa after thermal cycling at 1500 K for 100 h. Materials Science Institute, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5/6(395), pp. 69–75, May–June, 1997.     

Reaction kinetic,magnetic and microwave absorption studies of SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript>/CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> ferrite nanocrystals

Mixture of cobalt ferrite and strontium hexaferrite nanocrystals i.e. SrFe₁₂O₁₉/CoFe₂O₄ exhibiting super paramagnetic nature were synthesized by modified flux method. The resulting precursors were heat treated (HT) at 900 and 1200°C for 4 h in nitrogen atmosphere. During heat treatment, transformation proceeds as instantaneous rate of nucleation and three dimensional growth with activation energy of 135.835 kJ/mole. The hysteresis loops showed a hike in saturation magnetization from 1.045 to 84.362 emu/g with an increase in HT temperature. The ‘as synthesized’ particles have size in the range of 10–20 nm with spherical shape. Further, these spherical shape particles tend to change their morphology to hexagonal plates with increase in HT temperatures. The relative complex permittivity and permeability of the composite powder are investigated. The minimum reflection loss of the composite powder reaches to −27.6 dB at 10.8 GHz which suits its application in RADAR absorbing materials.     

Combustion synthesis of α-Si3N4-(MgO, Y2O3) composites

The possibility of obtaining composite powders of α-Si₃N₄-Y₂O₃ and α-Si₃N₄-MgO by self-propagating high-temperature synthesis (SHS) is studied. It is established that the α → β phase transformation starts at temperatures lower than the melting points of the corresponding eutectics. Metastable composite powders based on α-Si₃N₄ with a high rate of phase transition are obtained. The composite powders (α-Si₃N₄-Y₂O₃, α-Si₃N₄-MgO) are used in hot pressing technology. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 1–2(453), pp. 10–14, 2007.