Physico-Chemical Investigation of Component Interactions of the Si ― Al ― O ― N ― Ti System in the Region Si3N4 ― AlN ― Al2O3 ― SiO2 ― TiN ― TiO2. Part 1. Subsystems Si3N4 ― Al2O3, Si3N4 ― TiN,and Al2O3 ― TiN

Using the methods of differential thermal and x-ray diffraction analysis an investigation was made of component reactions in the Si Al O N Ti system, particularly between the compounds Si ₃N₄ Al₂O₃, Si₃N₄ TiN, and Al₂O TiN under conditions approximating those used in the hot pressing of composites. It was established that in the reaction of Si₃N₄ with Al₂O₃, -sialon, SiO₂, AlN, and the intermediate reaction products (mullite and X-phase) are formed. In the reaction of Si₃N₄ with TiN, as a result of the decomposition of Si₃N₄ at 1650-1900°C titanium disilicide is produced, which forms eutectics with free silicon and residual TiN at 1320 and 1280°C, respectively. The reaction of Al₂O₃ with TiN similarly leads to the formation of a eutectic between Al₂O₃ and spinel at 1850°C. The presence of eutectic liquids in the specimens after sintering promotes densification of the material, and improves certain of its mechanical properties.     

Study of Phase Formation Processes in the Systems Li ― N,Si3N4 ― Li3N,Si3N4 ― Li3N ― Y2O3

We have studied phase formation processes in the systems Li N and Si₃N₄ Li₃N. By nitriding lithium powder at temperatures of 400-600°C, we obtained lithium nitride Li₃N with a composition approaching stoichiometric. In the system Si₃N₄ Li₃N in the temperature range 300-1300°C, the ternary compounds Li₈SiN₄ (500°C), Li₅SiN₃, Li₂SiN₂ (900°C), and LiSi₂N₃ (1300°C) are formed. The studied properties of the hot-pressed composite material of the system Si₃N₄ Li₃N Y₂O₃ allow us to provisionally assign it to the class of solid electrolytes.     

Investigation of Liquid-Phase Sintering in W ― Sn ― Si Pseudoalloys

The kinetics of reaction between particles of tungsten and silicon during liquid-phase sintering of W Si Sn pseudoalloys was studied. Specimen growth caused by the formation of tungsten disilicide was observed. The growth rate in the investigated ranges of time and temperature obeyed a linear law. The rate constant was determined, and also the activation energy of the process, which agreed with the standard heat of formation of WSi₂.     

Thermodynamics of Component Interactions in Liquid Alloys of the Ternary Systems Ge(Al,Si) ― Ga ― Gd

The concentration dependence of the integral enthalpy of mixing in liquid alloys of the ternary systems Ge(Al, Si) Ga Gd at 1760 K, determined by the method of isoperibolic calorimetry and calculated using the surrounded atom model, was analyzed. Good agreement between H values obtained by both methods is noted. It was established that the interaction of gadolinium with components of the adjoining binary systems, which are characterized by the presence of intermetallic compounds, have a defining effect on the thermodynamics of alloy formation in the ternary systems Ge(Al, Si) Ga Gd.     

Effect of Mineralizing Agent on the Phase Composition of Nanocrystalline Powder in the System ZrO2 ― Y2O3 ― CeO2

The effect of mineralizing agent (AlF₃) on microstructural rebuilding and phase transformation that occurs during heat treatment in the range 600-1000°C for powder of the composition ZrO₂ 7 mole% CeO₂ 1 mole% Y₂O₃ is studied. The original nanocrystalline powder is prepared by high-temperature hydrolysis and sol-gel technology. It is established that during heat treatment there is decomposition of the solid solution based on T-ZrO₂ by a eutectoid reaction with formation of M-ZrO₂ and Ce₂Zr₃O₁₀. The compound Ce₂Zr₃O₁₀ is retained under these conditions at 1000°C. Anisotropic crystals of different chemical composition (M-ZrO₂, Ce₂Zr₃O₁₀, -Al₂O₃) form within the sintered matrix of a solid solution based on T-ZrO₂.     

Formation of a Corrosion-Resistant Layer on Steel by Reaction with a Si3N 4 ― Al2O3 Composite under the Conditions of Light-Thermal Treatment

The formation of a surface layer on low-alloyed steel during light-thermal treatment with a composite material based on Si₃N₄ Al₂O₃ was investigated. The working surfaces were studied using metallographic, x-ray diffraction, and electron-probe microanalysis. It was found that the corrosion-resistant phases Al₂SiO₅, (Fe, Cr)₂O₃, (Cr, Al) ₂O₃, and NiCrO₄ formed in the alloyed layer, increasing its microhardness by 2-5 times and its corrosion resistance in sea water by more than two orders of magnitude.     

Nitriding Powders in the System SiO2 ― Al2O3 ― C

Chemical and x-ray analysis methods are used to study features of carbothermal reduction and simultaneous nitriding of a powder mixture of crystalline SiO₂ (α-quartz) and amorphous SiO₂ (Aerosil). It is established that the use of amorphous SiO₂ leads to accelerated formation of SiC and a shift in the direction of nitriding towards AlN formation. It is also shown that both phases are the solid solutions SiC ― AlN and AlN ― SiC.     

The Solidus Surface in the Ti ― Ni ― Hf System in the Ti ― TiNi ― HfNi ― Hf Region

Studies have been done on the phase equilibria at subsolidus temperatures in the Ti TiNi HfNi Hf region of the Ti Ni Hf ternary system. The phases based on binary compounds and solid solutions of these components are accompanied in the equilibria by a phase based on an equiatomic ternary compound. This new phase belongs to the family of Laves phases and has a hexagonal crystal structure of MgZn₂ type. The solidus surface in the Ti TiNi HfNi Hf subsystem consists of the surface of the ternary phase alone, the surfaces of the six solid solutions based on the components and binary intermediate phases, the planes of five conode triangles, and the corresponding lineated surfaces.     

Effect of Y2O3, CeO2 on Sintering Properties of Si3N4 Ceramics

The effect of rare earth oxides Y203 or Ce02 on sintering properties of Si3N4 ceramics was studied and the mechanism of assisting action during sintering was analyzed. The results in dicate that the best sintering properties appear in Si3N4 ceramics with 5% Y203 or 8% CeO2. Secondary crystallites are formed at grain boundaries after heat treatment,which decreases the amount of glass phase and contributes to the improvement of high-temperature mechanical properties of silicon nitride.     

Regularities of Reactive Diffusion and Phase Formation in Ni ― Bi,Ni ― Zn,and Co ― Zn Binary Systems

Intermetallide layers enriched in bismuth or zinc are the first to grow in the Ni Bi, Ni Zn, and Co Zn reaction pairs. It is not found that high-symmetry phases of equiatomic composition are formed. There is not even a weak correlation between the rate of layer growth and the width of the homogeneity region for these intermetallic compounds. The main factors that determine the formation sequence for the intermetallic layers are the differences in melting point and atomic radius between the components, as well as the crystal structures of the intermetallides. The Kirkendall effect cannot be observed in the growing intermetallic layers. In that case, there is no physical basis for determining integrated diffusion coefficients.     

Equilibrium Phase Diagrams for the Dy ― Al ― B and Er ― Al ― B Systems

X-ray diffraction has been applied to component interactions in order to construct isothermal sections of the phase diagrams for ternary systems Dy Al B at 600°C (region above 50 at.% Al) and 800°C (region below 50 at.% Al) and Er Al B at 800°C. It is confirmed that there are ternary borides: DyAl₃B> _x (structure type BaPb₃, space group R , a = 0.6156(3) nm, and c = 2.109(1) nm), DyAlB₁₄ (type MgAlB₁₄, Imma, a = 0.5819(2) nm, b = 1.0380(3) nm, c = 0.8176(5) nm), ErAlB₄ (type YCrB₄, Pbam, a = 0.59258(7) nm, b = 1.1515(2) nm, c = 0.35340(6) nm), and ErAlB₁₄ (type MgAlB₁₄, Imma, a = 0.5819(1) nm, b = 1.0401(2) nm, c = 0.8189(1) nm). The {Dy, Er} Al B systems lack signs of solid solutions based on binary and ternary compounds.     

Model of Quasi-Isostatic Hot Pressing of SHS Products in the System Titanium ― Carbon ― Nickel. Part 2. Results of Modelling and Experimental Studies

Results are provided for modelling and experimental studies of hot quasi-isostatic pressing of SHS products of the system Ti C Ni. Good conformity is demonstrated between experimental data and calculated results using a rheological model for nonlinearly-viscous synthesis products. The model considers presence of a melt and the local nature of solid phase particle flow. Quantitative estimates are obtained for compaction of different zones of the loose shell, the force characteristics of the process, and the nonisostatic coefficient. This information is of interest for production planning and optimization of SHS product compaction.     

Investigation of the Structure and Properties of Materials in the SiC ― TiB2 System

The structure and properties of sintered and hot-pressed materials of the SiC TiB₂ system were investigated. The optimal conditions for obtaining dense ceramics with minimum grain size of the phase components was determined. It was established that composites containing from 25 to 50 vol.@percnt; TiB₂ have a bend strength equal to 450 MPa at 20°C; this increases to 500 MPa at 1600°C for ceramics with a pseudoeutectic structure. The material is highly heat resistant in the temperature range 900-1200°C.     

The Cr ― Ta ― C Melting Diagram in the (Cr) ― (Ta) ― (TaC) Region

It has been found from an experimental study on alloys in the Cr Ta C system in the region of the (Cr) (Ta) (TaC) subsystem at melting (crystallization) temperatures that there are two nonvariant four-phase equilibria of congruent type: L_E (Ta) + (Ta₂C) + (TaCr₂) at 1935°C and L_E (TaC) + (Cr) + (TaCr₂) at 1675°C; there is also one four-phase nonvariant equilibrium of incongruent transition type: L_U + (Ta₂C) (TaC) + (TaCr₂) at 1943°C, and two nonvariant three-phase equilibria of congruent type: L_e (Ta₂C) + (TaCr₂) at 1960°C and L_e (TaC) + (Cr) at 1695°C. The phase diagram for the subsystem has been constructed in the form of projections of the solidus and liquidus surfaces, and a melting diagram has been constructed.     

Solidus Surface and Phase Equilibria in Al2O3 ― ZrO2 ― La2O3 Alloy Crystallization

The projection of the solidus surface in the phase diagram for the Al₂O₃ ZrO₂ La₂O₃ system on the plane of a concentration triangle has been constructed, which consists of seven isothermal three-phase fields corresponding to three nonvariant equilibria of eutectic type and four nonvariant equilibria of peritectic type, as well as four lineated surfaces for the end of crystallization in the binary eutectics. The highest temperature on the solidus surface is 2710°C, and the lowest is 1665°C. No ternary phases and appreciable areas of solid solution are observed. Data on the bounding binary systems, liquidus and solidus surfaces have been used to construct the phase-equilibrium diagram together with a scheme for the reactions in equilibrium crystallization in the Al₂O₃ ZrO₂ La₂O₃ system.     

Phase Diagram of the Al ― Rh System

Phase equilibria in the Al Rh system over the range 15-50 at.% Rh were investigated by the methods of scanning electron microscopy, x-ray diffraction and electron-probe microanalysis.     

Phase Formation and Structure of Bronze ― Iron ― Graphite Composite Powder Material during Hot Forming

Copper tin iron graphite material prepared by hot forming is studied. It is established that on heating billets to 850°C Cu Sn alloy forms and there is no copper or tin in pure form after heating. The Fe Sn phase does not even form locally. Bronze grains have a banded relief that is connected with formation of a large number of twins and additional dislocations in Cu(Sn) solid solution. This structural inhomogeneity facilitates material strengthening and high operating properties.     

Reaction of Tungsten with Liquid Co ― Sn Alloys

The solubility of tungsten in Co Sn melts and the growth kinetics of a W₆Co₇ phase layer at the tungsten melt interface were studied at 1200°C. The liquid alloys composition in the three-phase equilibrium W W₆Co₇ melt was established as (at. fraction) 0.51 Co, 0.49 Sn, 2.3·10^–3 W. The solubility of tungsten in the investigated range of melt compositions is well represented by the equation lgx _W = –0.964-3.420x _Sn, where x _W and x _Sn are atomic fractions of the elements in the melt. The calculated thermodynamic properties can be used for the analysis of other systems which include cobalt and tungsten.     

原位制备细晶Si3N4-Si2N2O复相陶瓷

以Y2O3和Al2O3纳米陶瓷粉体作为烧结助剂，液相烧结非晶纳米Si3N4陶瓷粉体，制备Si3N4-Si2N2O复相陶瓷。Si2N2O相通过原位反应2Si3N4(s) 1．5O2(g)：3S12N2O(s) N2(g)生成。160012烧结，烧结体保温30min，Si2N2O体积分数达到52％，基本由细小均匀的球形晶粒构成。平均粒径尺寸210nm，相变过程中，个别颗粒异常长大，长径比达到1．5。保温时间对孔隙、密度和粒径产生重要影响：随着保温时间的延长，孔隙逐渐收缩减小，烧结体的致密度逐渐提高，晶粒逐渐长大，保温60min，孔隙几乎完全闭合，相对密度达到99．1％，平均粒径280nm。当保温时间达到90min时，相对密度增加并不明显，但平均粒径长大到360nm。     

Interactions in the Al2O3 ― ZrO2 ― La2O3 System at 1250 and 1650°C

Triangulation has been determined for the Al₂O₃ ZrO₂ La₂O₃ system, and 1250 and 1650°C isothermal sections of the phase diagram have been constructed. The LaAlO₃ La₂Zr₂O₇ section is quasibinary, while the LaAlO₃ T-ZrO₂ and La₂O₃ ·11Al₂O₃ T-ZrO₂ ones are partially quasibinary. The triangulation of the ternary system is based on ZrO₂ and a phase containing it. No ternary compounds or regions of ternary solid solutions have been identified.