Thermodynamic analysis of the reaction of titanium with boron carbide in a self-propagating high-temperature synthesis regime

Adiabatic temperatures, thermal characteristics, and the concentration of reaction products in the system Ti−B₄C containing 1–99 mass % B₄C are determined by thermodynamic analysis using the ASTRA package of programs. In order to prepare alloys of titanium with titanium boride and titanium carbide in a self-propagating high-temperature synthesis regime a mixture with 10–13 mass % B₄C is recommended, and for alloys of boron carbide with titanium carbide a mixture containing 53–70 mass % B₄C is recommended. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3–4(406), pp. 72–76, March–April, 1999.     

Oxidation of porous nanocrystalline titanium nitride. I. Kinetics

We used the continuous weighing method to study the oxidation kinetics in air for TiN specimens pressed and sintered from nanocrystalline powders with particle size ≤55 nm. Oxidation was carried out at 500–1000 °C for 240 min. By comparing with the oxidizability of compact titanium, we estimated the total reaction surface S of the porous specimens as a function of their oxidation conditions. The mass of absorbed oxygen Δm was calculated from the mass gain ΔP, taking into account the volatile component N₂. We have shown that the maximum mass gain Δm at 600 °C is due to reaction of oxygen with the largest reaction surface. Within 120 min, external pores close up, S decreases, and then a continuous oxide layer forms in which diffusion of oxygen is slowed down. At 700–800 °C, the process of closing up of the pores is activated, and S decreases by an order of magnitude compared to 600 °C. After the first 40–50 min, a continuous oxide film forms and virtually no further mass gain occurs. As the temperature increases, the oxidation rate increases. At 900 °C, the reaction surface becomes equal to the external surface of the specimen, but the thickness of the scale increases linearly. We hypothesize that for T > 850 °C, counterdiffusion of titanium ions is superimposed on diffusion of oxygen. __________ Translated from Poroshkovaya Metallurgiya, Nos. 1–2(447), pp. 98–103, January–February, 2006.     

Oxidation of porous nanocrystalline titanium nitride. II. Scale structure and composition

We have used x-ray phase analysis to study the composition of the products of reaction between oxygen and nanocrystalline powders with particle sizes 15, 40, 55, and 80 nm, and also specimens pressed (and sintered) from them. The powders were oxidized in air at 100°C (400 h) to 500°C (5 min), while the sintered specimens were oxidized at 600–900°C for 15, 120, and 240 min. In all cases, in the initial oxidation step the oxynitride Ti(O_xN_y) is formed, which over time is oxidized to TiO, Ti₂O₃, Ti₃O₅, TiO₂ (anatase) and TiO₂ (rutile). In the range 600–800°C, formation of a continuous oxide layer and conversion of anatase to rutile slows down diffusion of oxygen in the scale. We have established that at 900°C, the growth rate of the scale thickness increases and so the reflections from the oxynitride are barely noticeable on the diffraction patterns taken from the surface of the oxidized specimen. In these diffraction patterns, along with strong reflections from the rutile, we also observed weak reflections from lower oxides and anatase, which may be due to reaction between oxygen and the titanium ions diffused to the scale surface. We have concluded that at T > 850°C, the mechanism for oxidation of TiN changes. This is due to superposition of counterdiffusion of titanium ions on the diffusion of oxygen. __________ Translated from Poroshkovaya Metallurgiya, Nos. 3–4(448), pp. 72–78, March–April, 2006.     

Interactions of boron carbide with titanium and zirconium carbides under pressure

The reactions of boron carbide with titanium and zirconium carbides have been examined under various conditions. Reactive sintering of the initial mixtures produces a heterophase material based on B₄C–MeB₂ via a stage of lower boride formation. The reaction completeness is increased by adding boron and boron silicide. The material has a finely divided structure and high hardness (42–45 GPa). Promising mixture compositions have been identified together with ways of optimizing the sintering modes. Materials Science Institute, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos 1-2, pp. 52–55, January–February, 1998.     

Reaction of Titanium with Boron Nitride under Self-Propagating High-Temperature Synthesis Conditions

We have used the ASTRA computer program for thermodynamic analysis of the chemical reaction of mixtures of titanium with boron nitride in the composition range of 1-26 mass% BN under adiabatic conditions. We have calculated the adiabatic temperatures, the heat change, and the concentration of the reaction products. We have established that under self-propagating high-temperature synthesis (SHS) conditions, we can obtain alloys of titanium with titanium nitride and monoboride and alloys of titanium nitride with titanium borides. Experimental synthesis of the alloys under SHS conditions confirm the thermodynamic analysis results.     

Reasons for the formation of various titanium oxide phases upon wetting aluminum oxide with titanium-containing metallic solutions

The effect of the solvent metal on the composition of titanium oxides formed at the interface of a Ti-containing melt with Al₂O₃ was analyzed. The fact that titanium in dilute solution is oxidized to a higher degree than in the pure form is thermodynamically connected with the bond energy between the solvent metal and aluminum transferred from the alumina to the melt. Recommendations for controlling the oxygen concentration of the reaction products are given. Institute for Materials Science Problems, Ukrainian Academy of Sciences, Kiev. Donbas State Mechanical Engineering Academy, Kramatorsk. Translated from Poroshkovaya Metallurgiya, Nos. 3–4, pp. 27–33, March–April, 1997.     

Dielectric characteristics of sintered silicon nitride materials

We have studied and summarized data on structure formation and dielectric characteristics of Si₃N₄-based materials obtained by hot pressing and activated sintering. We have measured the dielectric characteristics in the frequency range 1 kHz to 10 MHz. We have established that the level of the dielectric characteristics of the materials is significantly affected by the content of highly dispersed Si₃N₄ powder obtained by plasmochemical synthesis in the original mix. Translated from Poroshkovaya Metallurgiya, Nos. 3–4(412), pp. 22–26, March–April, 2000.     

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.     

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.     

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.     

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.     

Corrosion behavior of zirconium diboride-based ceramics and electrospark coatings in 3% NaCl solution

The paper examines the corrosion behavior of AlN-ZrB₂, AlN-TiN, and ZrB₂-LaB₆ composite materials and associated electrospark coatings based on aluminum alloy AL9 in 3% NaCl solution. It is shown that the electrochemical corrosion resistance of composites is close to that of titanium nitride. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 1–2(453), pp. 54–57, 2007.     

Laws of capillary transport in porous materials prepared from titanium alloy VT6 fibers

A study was made of the kinetics of capillary absorption of ethanol in highly porous (70–75%) materials prepared from discrete fibers of titanium alloy VT6 (specimen dimensions 330×20×(0.4–1.3) mm). The fibers, 3 mm in length and 20–140 μm in diameter, were obtained by rapid solidification from the melt. Capillary transport against the force of gravity up to the equilibrium height of capillary rise was investigated in an atmosphere of saturated ethanol vapor. Experimental data on the rate of absorption were analyzed with reference to the properties of the pore space structure—effective pore size, tortuosity of the pore channels, and free surface area. The laws of capillary transport of ethanol in porous materials composed of titanium alloy VT6 fibers, discrete copper fibers, and grade VTEM-2 titanium powder were compared. It was shown that, with regard to the speed of absorption, the advantage of fiber materials over those made from powder is attributable to the less convoluted pore channels in the former. Materials Science Institute, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 1–2, pp. 67–74, January–February. 1997.     

Effect of titanium dioxide on the surface tension and density of an aluminocalcium oxide-fluoride melt

The effect of titanium oxides on the surface tension and density of an Al₂O₃-CaO-CaF₂ melt is studied. At 1773–1923 K, an addition of 4–25 mol % TiO₂ to an oxide-fluoride melt decreases the surface tension and increases the density. The complexation properties of titanium in the oxide-fluoride slags are revealed, and the size and character of the structural units are determined.     

Formation of the structure and phase composition of titanium nitride—(Nickel—Molybdenum) materials

The features of structure and phase composition of sintered heterophase materials based on TiN with Ni—Mo binder have been studied. Molybdenum in the binder increases the material density in comparison with that of nickel binder. This seems to be due to less release of nitrogen from TiN. After sintering, the binder consists of intermetallics of titanium with nickel and molybdenum, as well as solid solution based on nickel and molybdenum. The effect of Al₂O₃ additives (20%) on the microstrucutre and phase composition of TiN—Ni—Mo was also studied. Sintering in argon ambient and in vacuum results in increase of microhardness and lattice parameter of TiN caused by dissolution of nickel, molybdenum, and oxygen in TiN. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7–8(402), pp. 82–89, July–August, 1998.     

Matrix/reinforcement interactions in shock-wave consolidated titanium aluminide reinforced with SiC

Explosive shock-wave consolidation has been used to fabricate a composite consisting of gamma phase titanium aluminide matrix reinforced with paniculate silicon carbide. Although the consolidation process takes less than a microsecond to complete, melting of the surfaces of the titanium aluminide powder particles results in a reaction with the silicon carbide. Titanium suicide and titanium carbide form in the molten zone, depleting it of titanium to the extent that its final composition is TiAl₃. In addition, a second titanium suicide phase forms on the surfaces of the silicon carbide particles. This paper is based on a presentation made in the symposium “Interfaces and Surfaces of Titanium Materials” presented at the 1988 TMS/AIME fall meeting in Chicago, Illinois, September 25–29, 1988, under the auspices of the TMS Titanium Committee.     

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.     

Contact interaction of double titanium and chromium diboride with Fe-Cr alloys

The kinetics of wetting double titanium and chromium diboride by iron-based alloys with different chromium content is studied. It is shown that contact angles are formed in such systems over the range 0–10°. The energy parameters of wetting are calculated. It is established that chromium as a surface-active element promotes Fe-Cr alloy spreading on the diboride surface. The microstructure of the interaction area is studied. It is shown that terminal solid solutions and eutectics are formed in the TiCrB₂-(Fe-Cr) system. The optimum compositions of the metallic binder are determined for TiCrB₂-based composite materials. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 1–2(453), pp. 109–115, 2007     

Mechanisms of formation of the magnetic properties of powder metallurgy materials

The magnetic susceptibilities of powder titanium and nickel were measured over a wide range of porosities. the effect of consolidation during the sintering of conglomerates on the magnetic properties of the investigated materials was determined. The dependence of magnetic properties on porosity was explained on the basis of a physical analysis of the factors controlling the development of magnetic properties in powder materials. Altai State University, Barnaul. Translated from Poroshkovaya Metallurgiya, Nos. 3–4(400), pp. 36–38, March–April, 1998.     

Technology for the formation of gradient oxide composites

We have obtained functionally gradient materials by slip casting of aqueous suspensions of various oxide materials. We have produced gradient materials with 6 to 20 layers and layer thickness from 0.1 to 0.3 mm. We have determined the requirements for the starting powders and aqueous suspensions (pH, content of solid phase, stability relative to sedimentation). Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3–4(406), pp. 24–32, March–April, 1999.