Obtaining Fe—Ni—Co—Ti alloys having a thermoelastic martensite transformation

Using powder metallurgy methods, we have produced Fe—Ni—Co—Ti alloys that have a thermoelastic martensive transformation, which is the basis of the shape-memory effect manifested by such materials. Since pores are believed to improve the shape memory, specifically the reversible nature of the strain, attention was focused on development of the technology and investigation of the characteristics of porous Fe—Ni—Co—Ti alloys. The problems that arise during sintering of such alloys from sputtered powders are due to the chemical inhomogeneity of the initial structure and of the structure formed when the liquid phase appears. Various forms of activation, such as cyclic sintering and a stepped increase in temperature, were used to prevent the liquid phase from appearing. The properties of Fe—Ni—Co—Ti alloys with a shape memory effect can be improved if the porosity is increased by obtaining larger powder grains with a more complicated shape. Materials Science Institute, Ukrainian Academy of Sciences Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 1–2, pp. 79–85, January–February. 1997.     

Electric-spark alloying of structural alloys with a composite based on TiCN-AIN

The mass-transfer kinetics, the mechanism of formation, the tribotechnical characteristics, and the resistance to high-temperature oxidation of a coating formed on the hard alloy WC — 6% Co and on the titanium alloy VT6 by electric-spark alloying with electrode material based on TiCN — AIN with an Fe — Cr binder have been investigated. The phase distribution of the components in the coating was shown to be the same for both alloys. Electric-spark alloying of WC — Co and VT6 was found to reduce their wear by 33 and 60%, respectively. Moreover, the working temperature of the coated WC — Co alloy increased by 160 deg compared to the original surface. Translated from Poroshkovaya Metallurgiya, Nos. 5–6(413), pp. 21–29, May–June, 2000.     

Effect of electrospark alloying a tungsten hard alloy on its wear and corrosion resistance

An alternative to the surface modification of tungsten hard alloys by the PCVD method (from the point of view of economy and the level of useful properties) may be electrospark alloying (ESA). A study was made of the kinetics of mass transport in the ESA of a WC—6% Co alloy using an electrode material based on TiCN, and of the tribological properties and high-temperature oxidation resistance of the coated hard alloy. It was found that in the range of low and medium velocities (≤6 m/sec) linear wear of the WC—6% Co alloy was decreased by a factor of 22 by ESA, and the coefficient of friction decreased from 0.42 to 0.18. The untreated alloy suffered a catastrophic weight gain at elevated temperatures, while coated WC—6% Co retained statisfactory oxidation resistance. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5–6(407), pp. 42–47, May–June, 1999.     

Phase equilibria in the Cr-Ni-C system and their use for developing physicochemical principles for design of hard alloys based on chromium carbide

The Cr—Ni—C phase diagram at the melting point was plotted by a combination of procedures (metallography, x-ray, microprobe, differential thermal analysis, Pirani—Alterthum method, etc.). A general feature of this system is the existence of equilibria between the nickel-based phase and all the other phases. The temperature of the quasibinary (Ni)+(Cr₇C₃) eutectic was determined to be 1324±6°C. Based on both the phase diagram of the Cr—Ni—C system and the bending strength and Rockwell hardness of the alloys, the optimal composition of the initial carbide ingredient for production of hard alloys based on Cr₃C₂ with nickel—phosphorus binder was estimated as 13.0–13.3 at.%, substoichiometric with respect to Cr₃C₂. Institute of Problems in Materials Science, National Academy of Sciences of Ukraine, Kiev. Translated from Poroshkovaya Metallurgiya. No. 5/6(395), pp. 13–24, May–June, 1997.     

Structural features of Co-Si,Co-Ge,and Co-Sn binary melts

A comparative analysis of the local structures of binary Co— IVA Group element (Si, Ge, Sn) melts is performed using partial structural characteristics, which were calculated by three-dimensional mod els reconstructed from experimental structure factor curves by reverse Monte Carlo method. These melts are characterized by a common feature that consists in the existence of a marked interaction between atoms of different kinds, which are located at distances close to those in the corresponding intermetallics. Zigzag chains formed by covalently bound silicon and germanium atoms are found to exist in Co— Si and Co— Ge melts. This is due to the thermal dissociation of the intermetallics during melting and partial retention of the covalent bond between germanium atoms in higher germanides. In passing from Co— Si to Co— Ge and Co— Sn melts, a marked increase in the interaction between cobalt atoms takes place along with a decrease in the interaction between second-component atoms; in particular, this is especially typical of Co— Sn melts.     

Kinetics of interparticle contact formation during the laser sintering of two-component powders

The kinetics of interparticle contacts formation during the liquid-phase sintering of unlike materials under the action of laser irradiation was investigated. Trios of particles arranged in a row according to the schemes glass—polymer glass, metal—polymer—metal, and metal—glass—metal were sintered. The processes of particle approach and liquid neck formation between particles were studied. Possibilities for the manufacture of powder components with polymer and glass binders by the use of selective laser sintering followed by heat treatment are considered]. Institute of Technical Acoustics, Academy of Sciences of Belarus', Vitebsk. Translated from Poroshkovaya Metallurgiya, Nos. 5–6(407), pp. 37–41, May–June, 1999.     

Spectroelectrochemical study of molybdenum containing chloride melts

The behaviour of molybdenum(III) and (IV) ions in NaCl—2CsCl eutectic based melts at 550—750°C was studied using high temperature spectroelectrochemistry and cyclic voltammetry. Anodic oxidation of Mo(III) ions yields Mo(IV) containing melts. Mo(IV) — Mo(III) recharge is reversible. The values of the formal standard Mo(IV)/Mo(III) red-ox potential, ΔG of formation and mixing MoCl₄ in NaCl—2CsCl at 550°C are estimated.     

On the evaluation of stability of rare earth oxides as face coats for investment casting of titanium

Attempts have been made to evaluate the thermal stability of rare earth oxide face coats against liquid titanium. Determination of microhardness profiles and concentration profiles of oxygen and metallic constituents of oxide in investment cast titanium rods has allowed grActation of relative stability of rare earth oxides. The relative stability of evaluated oxides in the order of increasing stability follows the sequence CeO₂ — ZrO₂ — Gd₂O₃ — didymium oxide — Sm₂O₃ —Nd₂O₃ — Y₂O₃. The grading does not follow the free energy data of the formation of these oxides. A better correlation with the experimental observations is obtained when the solubility of the metallic species in titanium is also taken into consideration.     

Static-dynamic, forming of powder materials on a press—Hammer

The effect of combined static-dynamic pressing on the density of powder compact was studied. The regularities and advantages of static-dynamic compacting in a press—hammer were determined as well as the factors that influence densification and must be taken into account in calculations of powder loading in a press—hammer. Information on the development of die assemblies is presented. Donbas State Academy of Machine Construction, Kramatorsk. Translated from Poroshkovaya Metallurgiya, Nos. 7–8(402), pp. 5–9, July–August, 1998.     

Phase equilibria in titanium-rich alloys of the Ti — Fe — Nb — Al system

Isothermal cross sections at temperatures of 750°C and 550°C of the phase diagram of the quaternary system Ti — Fe — Nb — Al in the region of titanium-rich alloys for a constant aluminum content of 5 mass % were plotted using metallography, x-ray diffraction, and local x-ray spectral analysis. In the temperature range 550–750°C in alloys with 5 mass % aluminum, the maximum solubility of iron in α-titanium reaches ∼2 mass % for a niobium content of 3 ± 0.5 mass %. Translated from Poroshkovaya Metallurgiya, Nos. 3–4(412), pp. 27–32, March–April, 2000.     

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.     

Density measurements as an assessment of creep damage and cavity growth

The change in density during creep of several polycrystalline metals may be correlated through the expression —Δρ/ρ =B(∈t/d)(σ/G)^q exp (—Q _gb /RT) where —Δρ is the density change, p is the original density, e is the strain,t is the time,d is the linear intercept grain size,σ is the applied stress,G is the shear modulus,Q _gb is the activation energy for grain boundary diffusion,R is the gas constant,T is the absolute temperature, andB andq are constants withq ≃2 to 3. This expression is consistent with the theory of unconstrained grain boundary diffusion growth of cavities provided there is also concomitant strain-dependent nucleation. The expression does not support the power-law growth of cavities, growth by surface diffusion, or constrained grain boundary diffusion growth. Formerly Research Associate, University of Southern California.     

Capabilities of modern systems for monitoring and diagnosing equipment

The cost of maintenance and repair is one of the most important service characteristics of any technical system. It is almost impossible to minimize such costs without efficient monitoring of the condition of the system. In modern monitoring and diagnostic instruments—at least those used on rotating equipment—vibration is the main type of process that is analyzed and takes precedence over all other processes, thermal processes included. This is not only because vibration diagnostics is more efficient and is rapidly becoming less costly to perform, but also because it can be done at any time—including after several years of equipment operation, when the costs of preventive maintenance and repairs are usually no longer economically justifiable. VAST Company, St. Petersburg. Translated from Metallurg, No. 11, pp. 33–36, November, 1998.     

The weak link in drop-test simulations

Computer experiments based on a drop-test model show that the ductile component in sample fracture is much reduced by a random factor—the weak link. The weak link (measuring a few mm) must be transverse to the sheet surface and in the direction of impact. The weak link may be the primary boundaries formed in melt solidification. These boundaries, which are rich in impurities, alloying elements, and nonmetallic inclusions, may be inherited by the hot-rolled metal. In some cases, their stability may result in impurity retardation.     

Fire-resistant structural steels

The resistance of buildings and other facilities to fire depends on the extent to which their steel structures soften when heated to the temperatures created by the fire. A steel is generally considered fire-resistant if its strength when heated to such temperatures for short periods of time remains equal to 0.6–0.7 of its strength at room temperature. The alloying system Cr-Mo-V-Nb can be used for steels that are designed to be fire-resistant up to 700° C. The greatest resistance to fire — up to 800°C — is obtained in steels that contain boron. __________ Translated from Metallurg, No. 7, pp. 44–51, July, 2007.     

Increasing Potlife of Hall–Héroult Reduction Cells Through Multivariate On-Line Monitoring of Preheating,Start-Up,and Early Operation

Aluminum is produced inside metallurgical reactors known as pots that are replaced at the end of their service life. New pots are preheated, started, and then enter a period known as early operation in which different control strategies are used before entering regular operation. It is known that how preheating, start-up, and early operation are performed can damage a well-designed pot and lead to a shorter service life. However, the impact of these phases with respect to potlife is not well documented quantitatively. In this article, multivariate statistical analysis techniques are used to investigate the impact of pot-to-pot variations during the three phases. A partial least squares regression model is first proposed for predicting potlife, within an error of 90 days, using process data gathered until the end of early operation. This model is also used to identify those variables having the greatest influence on potlife. Finally, multivariate statistical process control charts are proposed to monitor the three steps efficiently. These charts have a low false-alarm rate and can help find the root cause of abnormal operation occurring during the early phases. A few examples are used to illustrate how operators and engineers could use the charts to maintain consistent early operation and help improve mean potlife. Nomenclature: In this article, bold characters are used to identify vectors (bold lowercase), matrices (bold capital), and three-dimensional arrays (bold, underlined capital). Lowercase italics letters are used to define indices. Al—Aluminium; Al₂O₃—Alumina; C—Carbon; CO₂—Carbon dioxide; kA—kilo-Amperes; Na—Sodium; Na₃AlF₆—Cryolite; V—Volt.     

Alloy behavior and the phase equilibrium diagram for the Sc-Ru-Rh system. Part 2. melting diagram for the Ru-ScRu-ScRh-Rh Partial system

Microstructure, x-ray phase, and microprobe analyses have been together with temperatures for the start of melting determined by the Pirani—Alterthum method in deriving the projection of the liquidus surface and crystallization scheme for the Ru—ScRu—ScRu—Rh partial system. The liquids surface is made up of five surfaces for the primary crystallization of solid solutions based on ruthenium and rhodium, phases based on the compounds ScRu₂, ScRh₃, and the δ phase (a continuous solid-solution series between isostructural phases of CsCl type based on ScRu and ScRh). There are the three nonvariant four-phase equilibria involving the liquid: L+(Rh)⇀(Ru)+(ScRh)₃ (1640°C) and L⇀δ+(ScRh₃)+(ru) (1520°C), which involve separate monovariant processes. Materials Science Institute. Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 1–2, pp. 31–35, January–February, 1997.     

“Stinol” yesterday, today, and tomorrow

In July of this year, the subsidiary of the NLMK—the “STINOL” Refrigerator Plant—produced its four-millionth refrigerator, thus cementing its reputation as a successful and dynamically growing company. Novolipetsk Metallurgical Combine. Translated from Metallurg, No. 10, p. 50, October, 1999.     

Using coke fines in the blast furnaces at OAO MMK

The influence of coke quality on its replacement by coke nuts is investigated. Analysis shows that, for coke of higher quality, a greater proportion may be replaced by coke nuts. When coke nuts fines are mixed with ore, the porosity of the batch is not impaired; on charging by means of a separate skip, by contrast, the porosity may be reduced by 5.7—7.6%. Hence, forcing of the furnace process is possible.     

Using the energy of a controlled explosion to break up large hard-to-process metal objects into scrap

Providing metallurgy, the most important sector of industry, with the raw materials it needs—particularly quality scrap and machining wastes—is an important and pressing problem for the nation’s economy. “Kontur” Research and Development Firm and the “Vtormet” Company. Translated from Metallurg, No. 6, pp. 23–26, June, 1997.