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.     

Phase Composition of Electrospark Tungsten Carbide-Based Coatings after Heating and Isothermal Soaking

A study of phase formation on electrospark coatings with WC Co Cu electrodes on R6M5 high-speed steel during isothermal heat treatment at the operating temperature of the coating. Copper tungstate CuWO ₄has been found to form, with its crystal lattice coherently bound to the basic carbide phase of the coating, tungsten monocarbide, through tungsten semicarbide as intermediary. The results complement the data on phase formation during the application of WC-based coatings and during their subsequent use with sliding friction.     

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.     

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.     

Optimization of Conditions for Plasma Spraying Coatings Based on Self-Fluxing Alloys with Additions of Zirconium and Hafnium Intermetallic Hydrides

The properties of coatings of self-fluxing PG-SR4 alloys with additions of Zr Fe and Hf Fe intermetallic compounds are studied as a function of the conditions of spraying onto 12Kh1MF steel. Air is used as the plasma-forming gas. A metallographic examination is made of the microstructure of the coatings and their microhardness is determined. The spraying process is optimized. A regression equation is obtained for the quality of the coatings.     

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.     

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.     

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.     

Stability and Heat Resistance of Silicide Coatings on Refractory Metals. Part 2. Stability and Heat Resistance of Silicide Coatings on Tungsten and Molybdenum at 1500-2000°C

The kinetics of diffusion redistribution of phases within the system WSi₂ W on heating tungsten silicide in air in the temperature range 1500-2000°C is studied. The stability and heat resistance of silicide coatings on tungsten is mainly governed by the diffusion of silicon towards the interphase boundaries W W₅Si₃, W₅Si₃ WSi₂, and WSi₂ SiO₂, formation at them of diffusion barriers of lower silicide W₅Si₃, and also a protective SiO₂ film at the outer boundary of the silicide coating. It is established that the transition rate for the higher to the lower tungsten silicide WSi₂ W₅Si₃ is on average four times slower than the transition rate for MoSi₂ Mo₅Si₃. It is shown that an increase in silicon concentration in the WSi₂ surface layer stimulates formation of diffusion barrier compounds at interphase boundaries. This leads to an increase in the stability of the phase composition and heat resistance of a silicide coating on metals. In particular at 1700°C the transition rate for molybdenum silicide on tungsten MoSi₂ (Mo, W)₅Si₃ is about twenty times slower than the transition rate for MoSi₂ Mo₅Si₃, and less by a factor of about eleven than the transition rate for WSi₂ W₅Si₃. Here there is also an increase in the heat resistance of silicide coatings on tungsten and molybdenum. It is shown that the SiO₂ film on tungsten silicide does not lose its protective properties up to 2000°C.     

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.     

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%).     

Mechanico-Chemical Synthesis,Structure and Properties of Alloys Based on the System Ti ― Al

The kinetics of structure and phase formation in Ti Al and Ti Al Sc alloy powders in the process of mechano-chemical synthesis from elemental powders was investigated. It was established that the formation of microdimensional x-ray amorphous composite particles with nanodimensional structural components occurs. It was shown that in consolidation of the mechanically alloyed powders by hot isostatic pressing structural heredity is realized, and that the materials produced have unusually high microhardness compared to that of similar cast alloys. This is characteristic of nanostructured materials. In addition to high hardness the materials are characterized by high work of plastic deformation at room temperature. Microalloying the alloy powders with scandium has a complex positive effect on the strength properties of the hot pressed materials, due to the formation of a dispersion hardened microstructure with purified nanodimensional grains.     

三种热喷涂工艺制备WC/Co涂层性能比较

分析比较了常规大气等离子喷涂、爆炸喷涂和超音速火焰喷涂的WC/Co涂层的形貌、显微组织、孔隙率、硬度、结合强度及其耐磨性。结果表明,超音速火焰喷涂和爆炸喷涂层性能相当,涂层具有与粉末相近的相结构,与大气等离子喷涂相比,涂层具有高的致密度、硬度和良好的耐磨性,涂层与基体的结合情况也得到很大的改善。     

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.     

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.     

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.     

Alloy Structure and Equilibrium Phase Diagram for the Sc–Ru–Rh System. Part 7. Polythermal Sections in the Sc–Ru–Rh System

DTA, XRD, metallography, and electron-probe microanalysis have been applied to study phase compositions of cast and annealed alloys (annealing at subsolidus temperatures of 1400°C (composition range 0-50 at.% Sc) and 930°C (composition range 50-100 at.% Sc)) and construct polythermal sections for the Sc Ru Rh ternary system on the isoconcentrates 75 at.% Sc, 65 at.% Rh, and beam Ru:Rh = 1:1, as well as isoconcentrates for 5.0 ± 0.3 at.% Ru and 5 at.% Rh in the region of 50-100 at.% Sc. The sections reveal characteristic features of the phase diagram structure for this ternary system, in particular temperature ranges for crystallization and the types of phase transformation within them.     

Stability and Heat Resistance of Silicide Coatings on Refractory Metals. Part 1. Effect of Subsurface Layer on Process of Phase Redistribution in System WSi2 ― W

The effect of a subsurface layer of metal silicide on the phase composition stability of high-temperature MeSi₂-type coatings on refractory metals was investigated. Using the system WSi₂ W as a prototype it was experimentally determined that a subsurface layer of the tungsten disilicide, and the distribution profile of silicon in the diffusion zone upon high-temperature heating have a substantial effect on the formation of a barrier layer of lower silicide which determines the stability of the system as a whole. It is proposed that the search for more stable silicide coatings on refractory metals should be directed toward the creation of diffusion barriers on not only the inner interface MeSi₂ Me, but also the external surface of the coating. The process of coating formation must be accompanied by the formation of a metal silicide on the external surface with the highest possible concentration of silicon.     

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.     

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.