Penetration of molten nickel into sintered titanium carbide hard metals

Conclusions A study was made of some aspects of molten nickel penetration into titanium carbide hard metals. It is shown that, when such a liquid phase migrates through a semiinfinite rod, the variation of the concentration of the binder metal along the length of the rod may be described by a hyperbolic function. The dependence of the thickness of the layer of increased nickel content on time of contact between the specimen and the melt was determined. It is demonstrated that, by employing the method of infiltration of a hard metal with a liquid metal, it is possible to produce parts possessing varying physicomechanical properties.Translated from Poroshkovaya Metallurgiya, No. 11(215), pp. 25–38, November, 1980.     

Interaction between nonstoichiometric titanium carbide and Fe-C alloys

This article describes a thermodynamic analysis, and the experimental verification, of the chemical interaction between nonstoichiometric titanium carbide and molten Fe-C alloys. The calculation and the analysis of the isothermal sections of the ternary Fe-Ti-C phase diagram in the 1500 °C to 1600 °C temperature range show that variations in composition and in the metal-ceramic ratio can occur in the course of the TiC _x -(Fe-C) composite preparation. These changes, in particular, those of the carbon content in the interacting phases, can affect the microstructure and properties of the resulting composite. The experimental results support the predictions of the equilibrium calculations, according to which nonstoichiometric titanium carbide tends toward the stoichiometric composition by absorbing carbon dissolved in the metallic binder or by releasing titanium to the melt. The microstructural observations also support the prediction that a significant amount of the carbide phase with a low carbon content can dissolve in the melt. The results of this study suggest that it is possible to design the microstructure of both the metallic and the ceramic phases in the composite by proper choice of the carbon content in the carbide phase. This allows the mechanical properties of the composites to be designed on the basis of thermodynamic considerations.     

Corrosion resistance of cermets based on titanium nitride

Conclusions The corrosion resistance of the cermets based on TiN with (Ni, Mo, Cr)-binder containing 10–15% Cr, is higher than that of KKhN-15 alloy and MNTs-20 German silver in solutions of acids: 5% HCl, 7% HNO₃ and 10% H₂SO₄.The resistance of the cermets based on titanium nitride is 5% HC1 decreases in the sequence: TiN-Cr > TiN-Ni, Mo, Cr > TiN > TiN-Ni, Cr > TiN-Ni, Mo > TiN-Ni.The corrosion resistance of the TiN-Cr cermets is slightly higher than the resistance of TiN. This is associated with the formation of the double nitride (Ti, Cr)N.Alloying theTiN-(Ni, Mo) cermet with 10–15% chrome results in high corrosion resistance and satisfactory physicomechanical properties.The corrosion resistance of the alloys with a high binder content (>25%) decreases as a result of its preferential dissolution which leads to separation of the titanium nitride grains. In addition to selective dissolution of nickel and molybdenum, the corrosion process in these alloys is also determined by dissolution of chrome.Translated from Poroshkovaya Metallurgiya, No. 1(337), pp. 77–81, January, 1991.     

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.     

Intermetallic compound layer growth at the interface of solid refractory metals molybdenum and niobium with molten aluminum

The growth mechanisms and growth kinetics of intermetallic phases formed between the solid refractory metals Mo and Nb and molten aluminum have been studied for contact times ranging from 1 to 180 minutes at various temperatures in the range from 700 to 1100°C. The growth of the layers of the resulting intermetallic phases has been investigated under static conditions in a saturated melt and under dynamic conditions using forced convection in unsatured aluminum melts. The Nb/Al interfacial microstructure consisted of a single intermetallic phase layer, Al₃Nb, whereas two to four different phase layers were observed in the Mo/Al interface region, depending upon the operating temperature. It was found that, in a satured melt, the intermetallic phase growth process was diffusion-controlled. The parabolic growth constants of the first and second kind and integral values of the chemical diffusion coefficients over the widths of the phases were calculated for both Mo/Al and Nb/Al systems. It also was found that the AlNb₂ phase grew between the Nb and Al₃Nb phases after consumption of the saturated Al phase. Similarly, the AlMo₃ phase grew between the Mo and Al₈Mo₃ phases with diminishing of all the other existing compound phases. In an unsaturated melt, the intermetallic phase layer grows at the solid surface while, simultaneously, dissolution occurs at the solid/liquid interface. This behavior is compared to the growth mechanisms proposed in existing theories, taking into consideration that interaction occurs between neighboring phases. It was found that the intermetallic phase, Al₈Mo₃, adjoining the base metal, was not bonded strongly to the base metal Mo and was brittle; its hardness also was larger than that of the layer near the adhering aluminum and the adjacent phases.     

Selection of the Optimum Electrolysis Bath Composition for the Synthesis of Holmium–Iron Triad Metal Intermetallics

The results of high-temperature electrochemical synthesis of holmium–iron triad metal intermetallics in chloride melts are presented. The influence of the current density, the composition of an electrolysis bath, and the synthesis time on the electrolysis processes and the composition of the end product is studied. The electrolysis of the molten KCl–NaCl mixture containing 0.5–2.5 mol % holmium trichloride and 0.1–2.5 mol % nickel (cobalt) dichloride at a current density of 0.5–2.0 A/cm², a temperature of 973–1073 K, and an electrolysis time of 30–90 min is shown to cause the formation of a cathode deposit in the form of a “metal–salt pear” on a tungsten electrode. This pear consists of a mixture of metallic nickel (cobalt) and HoNi, HoNi₅, and HoNi₃ (HoCo₂, HoCo₃, HoCo₅, Ho₂Co₁₇) intermetallics. The intermetallic compound content in the cathode deposit is found to increase at a constant current density (1.2 A/cm²) and when the holmium chloride content in a melt or the ratio of the holmium chloride concentration to the nickel (cobalt) chloride concentration increases. Only a mixture of holmium–nickel (cobalt) intermetallics can exist in the cathode deposit if the electrolysis bath composition and the electrolysis parameters are controlled. The electrochemical synthesis of holmium–iron intermetallics was performed under galvanostatic conditions in molten KCl–NaCl–HoCl₃. Iron ions are introduced in a melt via the anodic dissolution of metallic iron. The results of X-ray diffraction analysis of the electrolysis products demonstrate the fundamental possibility of synthesizing holmium–iron intermetallics. The optimum conditions of electrosynthesis of holmium–iron triad metal intermetallics are determined.     

Activity of titanium in Fe-Cr melts

The activity of titanium in Fe-Cr melts was measured using a galvanic cell technique. By measuring the activity of oxygen in equilibrium with the molten metal and solid titanium oxide, in conjunction with the analysis of the samples for titanium, the activity coefficient of Ti was measured at 1873 K. Oxygen cells, comprised of a thoria-yttria electrolyte with a Cr-Cr₂O₃ reference electrode and an Al₂O₃ (ZrO₂)-Mo cermet tipped molybdenum lead wire, were used to take the electromotive force (EMF) measurements. The measured values of γ°_Ti and e _Ti ^Cr were 0.018 and 0.1032, respectively.     

Reaction of a molten mixture of titanium,aluminum, and silicon oxides with hot-pressed silicon nitride

The formation temperature of a liquid phase and the solidification temperature of a molten mixture of Al₂O₃-TiO₂-SiO₂ oxides on a silicon nitride substrate are determined. Data are obtained for the change in kinetics. It is established that the intensity of interaction of molten Al₂O₃-TiO₂-SiO₂ with silicon nitride depends on the oxide mixture composition. With heating there are two possibilities: improvement and worsening of Si₃N₄ crystallite wetting with a liquid phase as well as solidification of the melt. The temperature range where a liquid phase exists for actual materials is about 15°C, which markedly worsens the process of structure formation with Si₃N₄ during sintering.Translated from Poroshkovaya M etallurgiya, No. 5, pp. 39–44, May, 1993.     

Behavior of Double-Oxide Film Defects in Al-0.05?wt pct Sr Alloy

The change in the composition of oxide layers and the possibility of the formation of bonding between the two layers of a double-oxide film defect when held in an Al-0.05?wt pct Sr melt was investigated. The defect was modeled experimentally by maintaining two aluminum oxide layers in contact with one another in the liquid metal at 1023?K (750?°C) for times ranging from 5?seconds to 50?hours. Any changes in the composition and morphology of these layers were studied by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The results showed that the A1₂O₃ layers started to transform to SrO gradually from the moment that they submerged into the melt. The transformation caused the two layers to bond with each other gradually. The results illustrated that the composition of the oxide layers of a double oxide film defect submerged in Sr-treated melt is different from that of pure Al, and this might affect the mechanical properties and the behavior of the defect in the melt significantly.     

Dilatometric investigations of the processes of liquid-phase sintering of materials of the Cu-Sn system

Conclusions The shrinkage of Cu-Sn powder compacts during liquid-phase sintering, which is due to dissolution of copper particles in molten metal and their regrouping, is preceded by growth caused by preferential diffusion of tin atoms from the liquid phase to the solid. The process of regrouping of solid-phase particles as a result of the destruction of the rigid skeleton of a compact at a high tin content at the instant of appearance of molten metal fails to manifest itself explicitly. The possibility cannot be ruled out that regrouping takes place at the instant of diffusional growth of compacts and, superimposing itself on the latter process, is responsible for the extent of relative growth being dependent on starting porosity.Translated from Poroshkovaya Metallurgiya, No. 9(261), pp. 27–31, September, 1984.     

A structural study of oxidation in an Al2O3 fiber reinforced titanium aluminide composite

A composite of titanium aluminide, reinforced with ZrO₂ toughened Al₂O₃ fibers, has been produced by pressure casting. The stability of the microstructure during vacuum and air annealing was investigated by scanning and transmission electron microscopy (TEM). Processing resulted in partial dissolution of ZrO₂ of the fiber into the molten metal which solidified into a two phase lamellar α₂ + γ matrix. Vacuum annealing caused dissolution of Al₂O₃ fiber into the matrix, transformation of the matrix into γ and precipitation of ZrO₂ and Al₂Zr within γ. During air annealing diffusion of O through the fiber resulted in the formation of Al₂O₃ coated ZrO₂ nodules extending from the fiber surface into the matrix in some regions and in the other regions the growth of Al₂O₃ into the γ of the lamellar matrix. An A15 phase with the metal composition, Ti₃Al₂, was found between the external oxide scale and the metal matrix.     

Laser melt injection of austenitic cast iron Ch16D7GKh with titanium

The results of studying the microstructure and microhardness of Ni-resist cast iron ChN16D7GKh after laser melt injection by means of introducing titanium particles into the melt are presented. The treatment was performed using a fiber laser with a beam focused into a spot 0.2 mm in diameter with a radiation power of 1 kW and the motion velocity of the laser beam of 10–40 mm/s. Titanium is dissolved in the cast-iron melt, and TiC particles are formed in the structure upon cooling. The coefficient of using the titanium powder increases as the fusion zone size increases and reaches 50% in the best case. A modified layer has a composite structure with a metallic matrix and a comparatively uniform distribution of titanium carbide particles. The microhardness of the modified zone is 600–700 HV. Its further growth is suppressed by the partial removal of carbon from the melt zone in the composition of red fume evolved in the process. Therefore, the Laves phase (TiFe₂) is formed instead of an increase in the TiC content upon increasing the titanium supply. The experimental data on the regularities of the weight loss caused by the substance removal from the melt zone depending on laser melting parameters are presented.     

Calciothermic reduction of titanium oxide and <Emphasis Type="Italic">in-situ</Emphasis> electrolysis in molten CaCl<Subscript>2</Subscript>

A concept for calciothermic direct reduction of titanium dioxide in molten CaCl₂ is proposed and experimentally tested. This production process consists of a single cell, where both the thermochemical reaction of the calciothermic reduction and the electrochemical reaction for recovery of the reducing agent, Ca, coexist in the same molten CaCl₂ bath. A few molar percentages of Ca dissolve in the melt, which gives the media a strong reducing power. Using a carbon anode and a Ti basket-type cathode in which anatase-type TiO₂ powder was filled, a metallic titanium sponge containing 2000 ppm oxygen was produced after 10.8 ks at 1173 K in the CaCl₂ bath. The optimum concentration of CaO in the molten CaCl₂ was 0.5 to 1 mol pct, to shorten the operating time and to achieve a lower oxygen content in Ti.     

Decomposition,Reduction and Dissolution Mechanism of Calcium Sulfate in Iron Oxide Dust Pellet

Iron oxide dust generated during oxygen blowing in the BOF process contains a high content of iron. This iron oxide dust can be used as a material of iron source in the BOF slag reduction process or as de‐siliconisation flux or dephosphorization flux of hot metal pretreatment. One of the most practical uses of iron oxide dust is recycling as a form of pellets in the BOF considering easy application and the amount that can be recycled. In the process of making iron dust pellets cement is used as a binder that contains a lot of calcium sulfate. This calcium sulfate is reduced and dissolved in the molten metal during refining in the BOF. If the oxygen content in slag and molten steel is high enough, the reduced sulfate cannot be dissolved into molten metal and it can be removed as SO_x gas. The behaviour of calcium sulfate has been studied using of 50kg high frequency induction furnace and industrial‐scale plant tests were carried out at a 300ton BOF. The results show that for low carbon steels the evaporation of decomposed sulfate increases with increasing oxygen content in the slag while for high carbon steels the decomposed sulfate is reduced into the molten metal.     

“Chemical vacuum”—A concept to be refined

The concept “chemical vacuum” is discussed, as applied to the carbon deoxidation of metallic melts. Melting in an argon atmosphere, which is chemical vacuum for the reaction of carbon-oxygen interaction in a metallic melt, is shown not to be equivalent to melting in physical vacuum. For melting in an argon atmosphere, the total gas-phase pressure over a melt is important, and the fact that an unmixed gas layer is likely to exist over the molten metal surface should be taken into account. The CO content in this layer is determined by the carbon and oxygen contents in the melt.     

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     

Calcium Production by the Electrolysis of Molten CaCl2—Part I. Interaction of Calcium and Copper-Calcium Alloy with Electrolyte

This paper describes the interaction between calcium and molten CaCl₂ and the solubility of calcium in this melt, depending on the calcium content in the copper-calcium alloy that comes in contact with the molten CaCl₂. The negative influence of the dissolved calcium on the current efficiency was verified. The negative effects of moisture and CaO impurities on the calcium current efficiency were demonstrated. The dependence of the current efficiency and the purity of the metal obtained by the electrolysis conditions were studied in a laboratory electrolyzer (20 to 80 A).     

Tri-phasic zirconia electrolyte for the in-situ determinations of silicon activities in hot metal

Tri-phasic zirconia electrolyte, which consists of cubic ZrO₂–MgO solid solution, monoclinic ZrO₂ and 2MgO · SiO₂, was applied to solid state electrochemical sensor for rapid determinations of silicon activities in hot metal. The performance of the cell: Mo + MoO₂ / tri-phasic zirconia electrolyte / Fe + Si + C was tested with molten iron at 1723 K. The cell potentials showed good sensitivity to the variation of silicon content in the melt.     

Regularities of the contact interaction of titanium carbide with Ni and Ni–Mo melts

Regularities of the dissolution, the phase formation, and the structure formation implemented under the contact interaction conditions of titanium carbide of various compositions with Ni and Ni–(5–25%)Mo melts are investigated. It is originally established that the dissolution of carbide TiC_x in nickel-based melts is incongruent. Preferentially, carbon transfers into the melt at x ≥ 0.9 and titanium at x ≤ 0.8. The limiting stage of the dissolution is diffusion of metal atoms in the liquid phase. The formation regularities of carbide Ti_1–nMo_nC_x (K-phase)—the main product of the contact interaction in the TiC/Ni–Mo system—are revealed. It is established that the K-phase is formed under the relative excess conditions of the Ni–Mo melt preferentially according to the dissolution–isolation mechanism. The composition of autonomous isolations of the K-phase depending on the experimental conditions (1450°C, 0–25 h) varies in limits from Ti_0.4Mo_0.6C_0.7 (a = 4.27 Å) to Ti_0.7Mo_0.3C_0.6 (a = 4.29 Å). It is determined by the molybdenum concentration in the melt at the unsteady dissolution stage and by the concentration ratio between titanium and carbon in it at the steady-state dissolution stage.     

Measurement of oxygen potentials in Ag-Pb system employing oxygen sensor

Accurate and instantaneous analysis of dissolved nonmetallic or metallic species in molten metals at elevated temperatures using an online electrochemical sensor is important for continuous process control during metal refining and alloying operations in metallurgical industries. In this article, the application of long-life, solid-state electrochemical sensors for oxygen has been demonstrated to measure the oxygen potential as a function of the lead concentration in a molten Ag-Pb system at 1323 K. Yttria-stabilized zirconia (YSZ) in the form of one end-closed tube 20 mm long, 3 mm inner diameter, and 1 mm wall thickness has been used as a solid electrolyte in the oxygen sensor. Electromotive force (EMF) of the solid-state electrochemical cell (−)Pt, Ni-NiO//YSZ//O _Ag-Pb, Mo(+) has been measured at 1323 K. The reference electrode consisted of Ni + NiO biphasic mixture; the working electrode was composed of a molten Ag-Pb alloy of varying concentrations of lead. The concentrations of lead in silver ranged from 0.02 to 10.20 wt pct. Samples of the molten alloy were drawn after each addition of Pb to Ag and analyzed by induction coupled plasma (ICP).