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.     

Synthesis of Alloy Ti ― 6Al ― 4V with Low Residual Porosity by a Powder Metallurgy Method

The possibility of producing titanium alloy Ti 6Al 4V with minimal residual porosity from mixtures of elemental powders by the method of pressing and sintering without hot deformation during or after sintering was investigated. Various powder mixtures based on titanium and titanium hydride with alloying additions of either elemental powders having different particle sizes, or master alloys, were studied. It was shown that the synthesis of Ti 6Al 4V from mixtures of titanium hydride and master alloys is optimal with respect to the attainment of high relative density. In this case the sintered material has density up to 99%, homogeneous microstructure with relatively small (100-120 m) -phase grains, and a low concentration of impurities, in particular oxygen, which provide a high level of mechanical properties (_ten = 970 MPa, = 6%).     

Increasing the Corrosion and Wear Resistance of Chromium Steel by Electrospark Alloying with an AlN–ZrB2–ZrSi2 Electrode

The effect of electrospark alloying (ESA) steel 40Kh with AlN ZrB₂ ZrSi₂ electrode material on the surface composition, structure, high temperature resistance to corrosion in air, anodic oxidation in a 3.0% NaCl solution, and also on the tribological properties was investigated. It was found that ESA substantially increases the corrosion resistance of the steel, and decreases the wear rate by an order of magnitude. The mechanism of corrosion of the ESA coating on steel 40Kh was determined. The corrosion process was retarded mainly by the presence of an Fe₂O₃ Al₂O₃ solid solution alloyed with chromium in the coating.     

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.     

Wear- and Scaling-Resistant Coatings Based on TiCN

The composition, structure, and properties of coatings obtained by the high-velocity gas-flame spraying of composite powders based on TiCN with additions of SiC, AlN, SiC AlN/Al₂O₃ and a binder of NiCr based alloy were investigated. The working surfaces of coatings were studied by metallographic, petrographic, x-ray diffraction, electron-probe analyses, and scanning electron microscopy. It was determined that coatings 200 m in thickness had a typical finely dispersed lamellar structure with layers enriched in titanium alternating with layers of NiCr alloy. The tribological properties of developed coatings were superior to those of the standard WC + 8% Co alloy: under dry friction at a load of 2 MPa and sliding velocities in the range 5-15 m/sec the coefficient of friction was 0.17-0.11, and wear rate 3.4-8.5 m/km. The high oxidation resistance of the coatings is due to the presence, in the outer scale layer, of refractory compounds Al₂SiO₅, (Cr, Al)₂O₃, and Al₂TiO₅, which prevent the diffusion of oxygen into the substrate. The mass gain of the coating based on TiCN SiC AlN was 1.42 mg/cm₂ at 1450°C.     

Structure and Properties of Ceramics Based on Tungsten and Titanium Borides and Boron Carbide

The W₂B TiB₂ B₄C ceramics studied were hot-pressed from composite powders synthesized by thermal reduction of boron carbide. The resulting materials have a skeleton structure with a boron carbide binder when the B₄C content is high and an inclusion-matrix structure when the B₄C content is low. The grain size varies from 5 to 20 m, depending on the preparation conditions. The composite has a hardness of 17.5-20 GPa with a strength in the range 500-1000 MPa.     

Interaction of Cerium Oxide with Hafnium,Zirconium, and Yttrium Oxides at 1500°C

Using the methods of x-ray diffraction and petrographic analysis as well as electron microscopy, phase relationships in the ternary systems ZrO₂ Y₂O₃ CeO₂ and HfO₂ Y₂O₃ CeO₂ were investigated over the entire range of concentrations at 1500°C. The accuracy of the phase relationships of the binary systems HfO₂ CeO₂, ZrO₂ CeO₂, and CeO₂ Y₂O₃ at this temperature was improved. Isothermal sections of the ternary phase diagrams at 1500°C were constructed. Specimens of various compositions were prepared from nitrate solutions by evaporating, drying, and heat treating at 1500°C. These systems are characterized by the formation of broad ranges of solid solutions based on C-Y₂O₃, F-CeO₂, F-HfO₂ and ZrO₂, and narrow ranges based on T-ZrO₂ and M-HfO₂. No new phases were detected. The course of isoparametric lines in the solid solution ranges of F-HfO₂ (ZrO₂) leads to the assumption that yttrium and cerium ions substitute for each other, but no appreciable substitution by them for zirconium or hafnium ions occurs.     

Structure and Wear Resistance of Coatings on Titanium Alloy and Steels Obtained by Electrospark Alloying with AlN ― ZrB2 Material

We have studied the process of electrospark alloying of titanium alloy VT6 and steels with a composite material based on AlN ZrB₂ with ZrSi₂ additive. We have established that Al₂SiO₅ and ZrSiO₄ forming in the coating directly during its formation play the role of a solid lubricant. Under optimal conditions for electrospark alloying of the titanium alloy, the coefficient of friction is 0.13, the wear is 6 m/km for a sliding velocity of 14 m/sec and a load of 2.56 MPa. Ceramics based on AlN ZrB₂ can be recommended for use as wear-resistant and corrosion-resistant coatings.     

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.     

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.     

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.     

Stability and Heat Resistance of Silicide Coatings on Refractory Metals. Part 3. Stability of Silicide Coatings on Niobium Heated in Air at 1500-1800°C

The kinetics of phase redistribution in the (Mo, W)Si₂ Nb system at 1500-1800°C was investigated. The kinetic parameters for growth of the lower silicides (Mo, W, Nb) ₅Si₃ + Nb₅Si₃ and decrease in the layer thickness of the higher silicide (Mo, W)Si₂ as function of the oxidation temperature were determined. It was established that the stability of the multiphase and multicomponent system was more than twice that of the system MoSi₂ Nb, and 15-18 times that of MoSi₂ Mo.     

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.     

Metal Chemistry of Scandium in Binary Systems Formed with Platinum-Group Metals as the Basis for Construction Multicomponent Systems Based on Those Metals

Major trends are considered in the physicochemical interaction in binary systems formed by scandium with the platinum metals (ruthenium, rhodium, palladium, osmium, iridium, and platinum) from the characteristic features of the phase diagrams and the use of metal-chemical factors governing the formation of intermetallides with various stoichiometry and structure types in those systems (the size, electron-concentration and electronegativity factors). The values for those factors have been established that are favorable to the formation of phases with Sc:Pt´ stoichiometry (Pt´ is a platinum metal), namely: 1:3 (structure type AuCu₃, 1:1 (CsCl type), 11:4 (Zr₁₁Os₄ type), and 44:7 (Mg₄₄Rh₇ type). Published data and the authors' own evidence on the structure of bounding binary systems have been used with evidence on the physicochemical interactions in the Sc Ru Rh system in forecasting the type of phase equilibria occurring in systems of Sc Pt´ Pt´ ´ type (where Pt´, Pt´´ = Ru, Rh, Pd, Ir).     

Sintering Densification and Microstructure Formation Kinetics in Silicon Nitride Ceramics

Research has been done on how the shrinkage rate and microstructure in the Si₃N₄ Al₂O₃ Y₂O₃ are dependent on temperature and nitrogen pressure during sintering. The shrinkage rate curves alter as the activator content varies. Additional densification may occur above 1800°C because of diffusion through the increased amount of liquid.     

Interactions in Molten Aluminum (Silicon) ― Boron Alloys

Isoperibolic calorimetry has been used to determine the partial and integral enthalpies of mixing for liquid alloys in the binary systems aluminum (silicon) boron at 1873 K. Those enthalpies are small exothermic quantities, which agree with published data. The enthalpies of mixing have also been calculated from the _f H ₂₉₈ of the metal borides. The concentration dependence has been determined for these enthalpies in binary alloys in the nontransition metal boron systems.     

Some Characteristic Features of Formation of Ceramics Based on Composite Powders SiC ― Si3N4 ― Si2N2O

We have studied the characteristic features of synthesis of composite powders SiC Si₃N₄ Si₂N₂O. We have investigated processes involving hot pressing of these powders without activating additives and a protective atmosphere. We consider the mechanical properties of ceramics obtained on the basis of these composite powders.     

Properties of Ni–Cr–Al Alloys Obtained by a Powder Metallurgy Method

Alloys of practically 100% density were formed by hot pressing mixtures of nickel, chromium and aluminum powders. The principal phases formed are solid solutions based on chromium, on nickel, and also the intermetallic NiAl. These correspond to phases in the phase equilibrium diagram of theNi Cr Al system. The strength and wear resistance of the alloys are determined by the ratio of phase components.     

Reaction of Stomatological Porcelain with Titanium and Titanium Nickelide during Sintering

The reaction of stomatological porcelain with titanium and titanium nickelide during sintering in the range 1050-1300°C was investigated. It was shown that when the sintering temperature is increased, silicides and other oxides are formed in place of the basic components (titanium and silicon oxides or titanium nickelide). Reactions in the porcelain titanium system take place in the solid state, but in the porcelain titanium nickelide system at temperatures above 1120°C they occur with the participation of liquid phases.     

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.