Phase equilibria in W-Fe-Co-Ni system alloys. I. Alloys containing 10% (Fe + Co + Ni) at 1400–1200°C

Conclusions The isostructural intermediate -phases of Fe₇W₆ and Co₇W₆ in the W-Fe-Co system form a continuous series of solid solutions and transformation of the L + peritectic equilibrium into, the similar L + (Co₇W₆), occurring in a narrow temperature range (1640–1630°C) is observed. In the W-Fe-Co-Ni system in the 1470–1460°C range transition of the L + (Fe₇W₆)+ peritectic equilibrium into the similar. L + (Co₇W₆+ is also observed.Upon completion of crystallization and at temperatures of 1400–1200°C alloys of the primary section with 10% (Fe + Co + Ni) have a two-( + or +) or three-phase (+ +) structure. In alloys rich in iron at temperatures below 1215°C FeW may form instead of (Fe₇W₆) phase.Translated from Poroshkovaya Metallurgiya, No. 4(280), pp. 60–64, April, 1986.     

The phase equilibria in W-Fe-Co-Ni system alloys. II. Isotherms of the solidus and the phase composition of alloys containing 10 and 20% (Fe + Co + Ni) at temperatures above 1200°C

Conclusions The isostructural intermediate -phases Fe₇W₅ and Co₇W₆ in the W—Fe—Co system form a continuous series of -solid solutions. In the 1640–1630°C range the L + (Fe₇W₆) peritectic equilibrium in this system changes to a similar L + (Co₇W₆) equilibrium, where is the tungsten-base boundary solution.In the W-Fe-Co-Ni polythermal tetrahedron in the 1470–1460°C range conversion of the L +(Fe₇W₆)+, peritectic equilibrium into the similar L + (Co₇W₆) + , where is the nickel-, -ironcobalt-base boundary solution, occurs.Upon completion of crystallization at 1400°C, the W-Fe-Co system alloys with 10–20% (Fe + Co) have a + phase composition, while the W-Fe-Co-Ni system alloys with 10–20% (Fe + Co + Ni) accordingly have + , + + or + . At temperatures below 1215°C in alloys rich in iron, FeW may be formed instead of -phase and therefore the alloys may have an + FeW, + + FeW, + + + FeW and + + FeW phase composition.Translated from Poroshkovaya Metallurgiya, No. 5(281), pp. 86–89, May, 1986.     

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.     

Reaction of Composite Ceramic Materials with Corrosionally Active Media

The oxidation of composite powders and monolithic AlN SiC, AlN SiC TiB₂, and AlN SiC ZrB₂ ceramics in air up to 1600°C was studied by the methods of thermogravimetric, differential thermal, x-ray diffraction, and electron-probe microanalysis. The exceptionally high corrosion resistance of these materials was established. The corrosion resistance and possibility of using structural ceramics of the systems TiB₂ AlN, TiB₂ TiN, and TiC_0.5N_0.5 in sea water was demonstrated. The toxicity of Si₃N₄, AlN, BN, and TiN powders was analyzed on the basis of their reactions with biochemical media. It was proven that TiN based materials are highly stable in the oral cavity.     

Densification of metal powders during heating under high pressures of up to 80 kbar

Conclusions An experimental study was made of the densification of metal powders during heating under pressures of up to 80 kbar. The character and kinetics of densification of powders during heating were found to differ markedly depending on whether the pressure applied to them was higher or lower than the critical pressure. It is demonstrated that the minimum necessary condition for attaining the density of the nonporous metal in the densification of a powder under the critical and higher pressures is the development of thermally activated dislocation motion processes in the range (0.3–0.4)T_m. The densification of powders at pressures below the critical is controlled by particle flow processes, its kinetics being strongly dependent on the applied pressure and temperature.Translated from Poroshkovaya Metallurgiya, No. 11(191), pp. 28–33, November, 1978.     

Phase formation processes and densification kinetics of the β-Si3N4 based sialon charges during sintering

Conclusions We studied the densification and phase formation processes during reactive sintering of the -sialon charges based on the -modification of silicon nitride with an insignificant weight content of aluminum. Densification of the charge occurs according to the regularities of the liquid phase sintering process during which the liquid phase disappears. The kinetics of densification and phase formation and the degree of completion of these processes depend on the composition of the original charge and the degree of dispersion of the powders of the additives. Under the present sintering conditions, the process of -sialon formation from -Si₃N₄ occurs according to the mechanism of dissolution and redeposition through a liquid phase with a significant contribution from the processes of mass transport through a gaseous phase.Translated from Poroshkovaya Metallurgiya, No. 8(296), pp. 56–62, August, 1987.     

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%).     

The effect of carbon content on the mechanical properties of tungsten carbide-cobalt hard alloys

Summary A study was made of the effect of graphite and-phase contents on the properties of VK8 alloy. It was found that, in the presence of the-phase in the alloy in the form of lakes or dendrites (lace), indicating carbon deficiency, the strength of the alloy is greatly reduced. Slight decarburization, taking the form of-phase formation along the interphase boundaries, has practically no effect on the strength of VK8 alloy. The presence of graphite in an amount of less than 0.5 vol. % has little effect on the wear resistance of VK8 alloy, and slightly raises its strength. A high graphite content substantially lowers both strength and wear resistance.     

Polythermal Ti-∑MoNi (9∶1) section of the ternary system Ti-Mo-Ni

Conclusions As a result of an investigation of the titanium corner of the system Ti-Mo-Ni, a partial phase diagram of the Ti + (0–55%) MoNi (91) section was constructed. The solubility of Mo and Ni in-Ti is 0.65% MoNi. Thea + phase field is bounded by MoNi contents of 0.65 and 17% at 600°C, 0.5 and 14% at 700°C, and 0.4 and 6% at 800°C. At MoNi contents of 55% and higher, there is a + Ti₂Ni field, the existence of which was confirmed by x-ray structural studies.Translated from Poroshkovaya Metallurgiya, No. 2 (110), pp. 33–37, February, 1972.     

Mechanical treatment of powders of refractory carbides

Conclusions The model of mechanical treatment constructed in this work makes it possible to reduce all the parameters of this treatment to three generalized parameters: the mean energies of movement of the spheres_s, particles _p, and the fraction of absorbed energy . The main input parameters of the conditions are the vibrational speed V_a = A and the flow of the powder qv.On the basis of calculations of the energy characteristics of mechanical treatment of the powders of the tantalum carbides and semicarbides we can estimate the contribution of mechanical energy of this treatment to the activation of the processes of synthesis of the semiand subcarbides of these metals. Specifically, the effect of synthesis of the refractory tantalum semicarbide directly in the chamber of the vibratory mill during mechanical treatment can be explained.Translated from Poroshkovaya Metallurgiya, No. 4(280), pp. 91–96, April, 1986.     

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.     

Buckingham-potential parameters and relations between them for solids

Parameters m and n in the Buckingham potential in the form =[U₀mn/(m – n)]{(1/m)Y^–m – (1/n)exp[n(1–Y)]} have been calculated for 79 elements and 35 compounds, which have been compared with data on =c_v/(U₀) and =KV₀/c_v, in which U₀ is the cohesion energy, Y=(V/V₀)_1/3, V a volume with equilibrium value V₀, ... c_v the specific heat, the thermal-expansion coefficient, and K is the bulk elastic modulus. It is found that m is dependent essentially on and n on . These relationships have been approximated, and conclusions are drawn from them about the most reliable input data, particularly K because of the large spread in published values. A study is made on the relation of m and n to the positions of the elements in the periodic system and the electron structures.Institute of Problems of Materials Sciences, National Academy of Sciences of the Ukraine, Kiev. Translated from Poroshkovaya Metallurgiya, No. 5–6, pp. 118–126, May–June, 1994.     

Corrosion of Titanium-Aluminum Intermetallides. Part 2. Electrolytic Oxidation of γ‐TiAl,TiAl3, and α2‐Ti3Al in Sea Water

Potentiodynamic polarization, XRD, Auger electron spectroscopy, and scanning electron microscopy have been applied to determine the mechanisms of electrolytic corrosion of the intermetallides TiAl, TiAl₃, and ₂Ti₃Al in 3% NaCl solution with the addition of MgSO₄ in comparison with the corrosion of the pure metals (Al and Ti). There is comparatively high corrosion resistance in TiAl and Ti₃Al because of the protective action from thin films of rutile TiO₂. Evidence is obtained for the differences between these intermetallides from the appearance of pure titanium on deep anodic polarization (above +0.15 V for TiAl and +0.7 V for Ti₃Al): the aluminum and titanium enter the solution in the forms of Al³⁺ and TiO²⁺ and intermetallides dissolve rapidly. The final solid-state products from anodic oxidation in that case are rutile, magnesium aluminate, and also magnesium and sodium titanates. In addition to pure titanium, TiAl and ₂Ti₃Al as constructional materials may be recommended for use in sea water.     

Error in the determination of the particle-size distribution of a powder with a laser analyzer

Conclusions Simple expressions have been obtained from known parameters of a flow-type chamber for estimating errors in laser analyzer measurements of the main numerical particle size distribution characteristics of powders obeying the logarithmic normal law. It is shown that, in spite of marked errors (Fig. 1) in size measurements on single particles whose trajectories are deflected from the laser beam center, it is possible to attain high accuracy in the measurement of numerical particle distribution characteristics by suitable choice of aero or hydrodynamic particle stream focusing [5] (Table 1: maximum error in the determination of the amount of the main fraction in a powder of particle size 3/2 _f = 1.9% at 2_j = 15 and _f = 4.3% at 2_j = 72 m). Without good particle stream focusing, measurements may be very inaccurate (Table 1: _f = 24% at 2_j = 120 m and _f = 55.5% at 2_j = 170 m). The accuracy of laser analyzer measurements grows with increasing curvature (coefficient n) of analyzer calibration characteristics and vice versa. The q/qt relationships obtained may find application in the assessment of errors in particle size analyses of powders with particle distributions differing from the logarithmic normal law.Translated from Poroshkovaya Metallurgiya, No. 12(288), pp. 15–20, December, 1986.     

Stability of liquid metallic interlayers during the sintering of heterophase composites. I. Two-phase systems

Conclusions For composite materials of the first type (_ss > 2_s), there exists a critical liquid interlayer thickness above which they do not form or are unstable. At a channel thickness smaller than the critical, liquid interlayers at first form spontaneously by migration of molten metal from within the part into the channel, and subsequently they become filled by growing refractory particles. In composite materials of the second type (_ss 2_s), liquid metallic interlayers of all sizes are stable.Translated from Poroshkovaya Metallurgiya, No. 1(337), pp. 11–17, January, 1991.     

Phase relations in the Ti-TiNi-NbNi-Nb region of the ternary system Ti-Nb-Ni

We have used microstructural, differential thermal, x-ray phase, and electron probe analysis to study alloys in the Ti-TiNi-NbNi-Nb region of the ternary Ti-Nb-Ni system, both as-cast and annealed at 900°C. We have located a pseudobinary TiNi- section, where is a Nb-rich (Nb, Ti)-based solidsolution. The pseudobinary eutectic point parameters are 1170°C and 38 Ni 26 Nb (at. %). We have found two invariant peritectic four-phase equilibria for crystallization of the alloys in the region of interest: L + TiNi + Ti₂Ni (950 °C) and L + TiNi + NbNi (1140°C). We have not confirmed the existence of a ternary compound Ti₃(Ni,Nb)₂.Institute of Materials Science Problems, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3/4, pp. 48–54, March–April, 1995.     

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.     

Deposition of chromium coatings on diamonds from a gaseous phase

Conclusions A thermodynamic analysis of the reaction of diamonds with a gaseous chromium iodide phase has enabled the optimum conditions of coating deposition on diamonds to be determined. It has been established by experiment that treatment for 0.25–1.0 h at temperatures ranging from 700 to 1000°C results in the deposition on diamonds of 0.1- to 2.0-m-thick layers composed of the chromium carbides Cr₇C₃ and Cr₃C₂, Cr₇C₃ being the first to form.Translated from Poroshkovaya Metallurglya, No. 4(232), pp. 46–49, April, 1982.     

Melting points and microhardness of germanides of the cerium-subgroup rare-earth metals and yttrium

Summary The melting temperatures and microhardness of germanides of the rare-earth metals of the cerium subgroup and of yttrium were determined. The melting temperature and microhardness of lanthanum, cerium, praseodymium, and neodymium increase with increasing atomic number of the rare-earth metal and also in the series Me₅Ge₃MeGeMeGe₂. The germanide phases of yttrium exhibit a different relationship: Melting temperature and microhardness attain maximum values for the phase Y₅Ge₃ and decrease in the series Y₅Ge₃YGeYGe₂.Translated from Poroshkovaya Metallurgiya, No. 7 (79), pp. 51–54, July, 1969.     

Thermodynamic properties of alloys of the manganese-silicon system in the ranges of existence of the silicides “Mn9Si9” and “Mn6Si”

Conclusions The Gibbs energy, enthalpy, and entropy of formation of phases based on the compounds Mn₉Si₂ and Mn₆Si at 690–850°C have been determined by measuring the emf's of concentration galvanic cells.Translated from Poroshkovaya Metallurgiya, No. 7(235), pp. 67–70, July, 1982.