Electrodeposition of coatings of double carbides of tungsten and molybdenum from tungstate–molybdate–carbonate solutions

The electrochemical deposition of coatings of double tungsten and molybdenum carbides from tungstate–molybdate–carbonate melts is investigated. The composition of formed coatings is investigated by X-ray fluorescent and X-ray phase analyses. The crystal size and coating thickness are determined using scanning electron microscopy. Optimal deposition parameters of W₂C · Mo₂C coatings are as follows: the melt composition is Na₂WO₄–(1.0–4.0 mol %) Li₂WO₄–(1.0–4.0 mol %) Li₂MO₄–(1.0–5.0 mol %) Li₂CO₃, the cathode current density is 750–1500 A/m², the process temperature is 1123–1173 K, and the electrolysis duration is 4 h.     

Discontinuous coarsening of the lamellar structure of γ-TiAl-based intermetallic alloys and its control

Discontinuous coarsening (DC) of the primary lamellar structure (PLS) occurring at lamellar colony boundaries (LCBs) and in surface layers of various Ti-(40 to 45) at. pct Al binary and Ti-46 at. pct Al-X (X=Si and C) ternary alloys was systematically investigated by using optical microscopy and scanning and transmission electron microscopy. The compositions of the α ₂ and γ phases in the primary lamellar structure were estimated based on the weight fractions of the two phases, determined by X-ray diffraction. When the solution-treated Ti-(40 to 45) at. pct Al binary alloys were subsequently soaked at 1000 °C, the primary lamellae in the Ti-40 at. pct Al alloy were the most stable, while those in the Ti-44 at. pct Al were the most unstable. Both the thermodynamic analysis and experimental results confirm that the driving force of the coarsening is mainly derived from the reduction of the chemical free energy (i.e., out-of-equilibrium chemical composition) and the interfacial energy of primary lamellae, whereas the coarsening resistance is mainly from the increase of the elastic strain energy of lamellar interfaces and the surrounding during coarsening. It is found that Si has an exceptional ability to hinder the coarsening of the primary lamellar structure at high temperatures, but the precise mechanism for this improvement is uncertain now. Based on this study, a proposal is finally addressed to improve the thermal stability of the primary lamellar structure of titanium aluminides.     

Grain refinement of aluminum alloys: Part I. the nucleant and solute paradigms—a review of the literature

Despite the extensive literature on grain refinement, there is not a consensus on the mechanism of grain refinement in aluminum alloys. Recently, there has been a shift in understanding of the grain-refinement paradigm from purely being concerned with the nucleation event, called here the “nucleant paradigm,” to also being concerned with the effect of solute elements, or, the “solute paradigm,” on the final grain structure. This article is divided into two parts. In Part I, the literature underpinning both paradigms is explained, and the validity of the paradigm shift toward the solute paradigm as a more complete understanding of grain refinement is presented. Part II experimentally confirms the validity of the solute paradigm and details a mechanism which explains the need for both effective nucleants and a solute of a good segregating power in order to obtain grain refinement.     

Oxidation resistance and strength of a molybdenum fiber–oxide matrix composite material

The oxidation kinetics of a composite material, which consists of an Al₂O₃–Al₅Y₃O₁₂ matrix and molybdenum fibers and has a high cracking resistance, is studied. The mass loss of the composite material during oxidation is shown to be several orders of magnitude lower than that of molybdenum. Oxidation in quiet air at 1250°C for several hours weakly changes the strength of the composite material at temperatures from room temperature to 1300°C. It is also shown that the strength of the composite material as a function of the oxide matrix composition (Al: Y ratio) changes nonmonotonically. The maximum strength shifts from the Al₂O₃–Al₅Y₃O₁₂ eutectic point toward garnet.     

Largest domestic tungsten and molybdenum deep processing project finding its home in Luan-chuan

Recently, a tungsten and molybdenum deep processing project was formally executed with a joint investment of 300 million yuan from Luanchuan Molybdenum Mining & Smelting Co., Ltd, Beijing Tian-Long Tungsten & Mo-     

Effect of stress and temperature on the creep and rupture behavior of a 1.25 Pct chromium—0.5 Pct molybdenum steel

The creep and stress rupture behavior of a normalized 1.25 pct chromium-0.5 pct molybdenum steel has been investigated over a temperature (T) range of 510 to 620°C and a stress(σ) range of 65 to 425 MN/m². The creep rate ( ) and time to rupture (t _r ) data have been analyzed in terms of the general expression ort _r -A σⁿ exp (Q/RT), whereA is a constant,n is the power exponent of stress,Q is an empirical activation energy for the rate controlling process andR is the universal gas constant. At each temperature, the logarithmic plots of creep rate and time to rupture as functions of stress consist of two linear segments, separating the data into low stress and high stress regimes. The stress exponent has approximate values of 4 and 10 in the low stress and high stress regimes respectively in the appropriate expressions for both creep rate and for time to rupture. The activation energy has values of 367 and 420 kJ/mole in the low stress regime for time to rupture and creep rate respectively. In the high stress regime, the respective values of activation energy are 581 and 670 kJ/mole. Fractographic observations show that the changes from low stress to high stress behavior in creep rate and time to rupture approximately coincide with the transition in fracture mode from intergranular to transgranular cracking as well as with the transition in the rupture ductility from a region of linear variation with stress to one of constant ductility. These observations suggest that the transition from low stress to high stress behavior may be associated with a change in deformation mode from predominantly grain boundary sliding at low stress to transgranular matrix deformation at high stress. Analysis of the creep rate data based on this premise enables calculation of the ratio of the contributions of the grain boundary sliding mode to the total deformation (ε _gb /ε _T ) at various values of stress and temperature. Results of this analysis are consistent with numerous experimental observations reported in the literature.     

Application of resins with functional groups in the separation of metal ions/species – a review

ABSTRACT

This article presents a comprehensive review of polymeric resins used for metal separation in hydrometallurgy and water/wastewater treatments. The adsorption selectivity of a resin depends on the characteristics of the functional group and solution pH. The resins are reviewed and categorized with respect to the principal acting atoms in functional groups (i.e., nitrogen, sulfur, phosphorous, oxygen) and ion-exchange properties. General selectivity trends, metal ion preferences, and applications reported in the scientific literature are summarized for each functional group. This review is intended as a reference for the selection of ion-exchange resins for metal separation and recovery. The selection criteria also depend on the type of process and metal ion concentration.     

Electrodeposition of Rare Earth Metals and Their Alloys in Organic Electrolytes

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Consolidation of diamond tools using Cu–Co–Fe based alloys as metallic binders

Abstract

The present work reports the results obtained on the evaluation of both the response of commercially available Cu–Fe–Co pre-alloyed powders during processing for the consolidation of diamond tools under several fabrication routes, and the performance of the tools during in field cutting operations. The new metallic binders look attractive since they combine good sinterability with adequate values of hardness and wear resistance, as observed from the cutting tests carried out on granite and marble. The consolidation routes under research were conventional hot pressing, pressureless sintering, and hipping after sintering. The amount of copper contained in these alloys leads to fully dense parts by hot pressing at temperatures approximately 150°C lower than those used for cobalt. Pressureless sintering experiments showed that full densification requires the application of hipping post-sintering treatments. During processing under non-reducing atmospheres, the presence of metallic oxides contained in the powder was observed to exert a direct influence on the degradation of the diamond grits.     

Electrodeposition of cobalt–tungsten alloys from alkaline citrate containing bath as alternative for chromium hexavalent replacement

Abstract

Cobalt–tungsten alloys have been considered as potential materials for various applications. This work investigates the wear and corrosion resistance behaviour of cobalt–tungsten–phosphorus alloys electroplated from alkaline citrate containing baths. The wear rates of the cobalt–tungsten alloy electrodeposits were lower than those of the unalloyed cobalt electrodeposits. The wear rate was also lower than those of chromium plated from hexavalent chromium plating bath. It was also demonstrated that the addition of small quantities of phosphorus into Co–W alloys improved the corrosion resistance of the alloy. In fact, the addition of phosphorus further improved the corrosion of the alloy exposed to immersion test in comparison to cobalt–tungsten. The cobalt–tungsten alloys without having any phosphorus component were subjected to further oxidation of tungsten component followed by dissolution in deionised water during the immersion tests.

On a considéré des alliages de cobalt et tungstène comme matériaux potentiels pour diverses applications. Ce travail examine le comportement d’usure et de résistance à la corrosion d’alliages de cobalt, tungstène et phosphore déposés par électrolyse, à partir de bains alcalins contenant du citrate. Les taux d’usures des dépôts de l’alliage de cobalt et tungstène étaient plus faibles que ceux des dépôts non alliés de cobalt. Le taux d’usure était également plus faible que ceux de chrome déposés à partir d’un bain de dépôt électrolytique de chrome hexavalent. On a également démontré que l’addition de petites quantités de phosphore dans les alliages de Co–W améliorait la résistance à la corrosion de l’alliage. En fait, l’addition de phosphore améliorait davantage la corrosion de l’alliage exposé à un essai d’immersion par rapport à l’alliage au cobalt et tungstène. Les alliages de cobalt et tungstène, sans la composante de phosphore, étaient sujets à davantage d’oxydation de la composante de tungstène suivie par la dissolution dans de l’eau déionisée lors des essais d’immersion.     

The critical resolved shear stress of a superalloy as a combination of those of its γ matrix and γ′ precipitates

The critical resolved shear stress (CRSS), τ ₀, of peak-aged single crystals of the γ′-hardened commercial nickel-base superalloy NIMONIC 105 has been measured as a function of temperature T and orientation [hkl] of the compression axis. The same measurements have been carried out for the two constituent phases of NIMONIC 105: for the single-phase γ matrix and for the single-phase L1₂-long-range ordered γ′ phase. The value of T ranged from 283 to 1150 K, and the following orientations were studied: [001], [011], , and . The specimens were compression tested. The τ ₀ values of NIMONIC 105 and of the γ′ phase are anisotropic; the anisotropy of NIMONIC 105 is similar to that of the γ′ phase, but less pronounced. The τ ₀ of the γ phase is isotropic. The τ ₀ values of the γ and of the γ′ phase vary with T, whereas the τ ₀ of NIMONIC 105 is nearly independent of T for 400 K≤T≤1000 K. A model is presented that relates the function τ ₀ ([h, k, l], T) of NIMONIC 105 to the analogous functions of its constituent γ and γ′ phase.     

China''''s imports and exports of tungsten,molybdenum,tin and antimony by category

~~China's imports and exports of tungsten,molybdenum,tin and antimony by category~~     

Electrodeposition and morphology of Ni–Co alloy powders by constant and pulsating overpotential electrolysis

Powder Metallurgy and Metal Ceramics - The polarization dependences are recorded and the conditions of Ni–Co powder formation in amino-chloride electrolyte are found for different proportions...     

Unique metallic glass formability and ultra-high tensile strength in AlNiFeGd alloys

The metallic glass formability of aluminum-rich AlNiFeGd alloys has been systematically investigated. The critical cooling rate required to form an amorphous state in this system is generally low, and comparable to that of some of the best metallic glass formers, such as PdCuSi. Amorphous ribbons up to 0.25 mm thick can easily be produced by the single-roller melt-spinning technique. Tensile strengths as high as 1280 MPa and Young's modulus of 75 GPa have been obtained. Bulk amorphous alloys with good mechanical properties are optimized in Al₈₅Ni₆Fe₃Gd₆. DSC and DTA studies reveal that the glass formability is unique for Al-based alloys because the reduced glass temperature T_rg for AlNiFeGd can be as low as 0.44. This is much lower than conventional theory would suggest for easy glass forming systems. A mechanism for the unusual glass formability is suggested.     

Laser surface alloying of nickel by molybdenum and aluminium— microstructural studies

It is now well established that a considerable improvement in the mechanical and chemical properties of the near surface regions of materials may be achieved by the use of high energy laser beams. By manipulating the laser power density and the time of interaction of the laser beam with an appropriately coated work piece, it is possible to achieve a surface chemistry that would have an improved resistance to wear, fatigue and corrosion failures. The change in chemistry at the surface is attained through the process of melting and mixing of the coating and a thin layer of the substrate. Solidification of this molten region at the surface results, due to an interplay of various forces, in the development of very complex microstructures. To analyse these in a piece of nickel that had been coated with a mixture of molybdenum and aluminium powders and then treated with a continuous wave CO₂ laser, extensive transmission electron microscopy was done on a thin foil obtained from near the bottom region of the recast pool. The foil was found to have a cellular microstructure comprising cells of the Ni₃Al (γ′) ordered phase. In the intercellular regions, two dispersed phases, namely, martensitic Ll₀ phase and Ni₂Al₃, and a contiguous phase, identified as a close derivative of the equilibrium δ-NiMo phase were found. A gradient in the degree of order could be observed within the γ′ cells. In the central portion of the cells, rapid solidification resulted, by the process of sequential ordering, in the development of a partially ordered alloy with very fine domains. In the peripheral regions of the cells, the alloy solidified by direct ordering into larger domains. This paper discusses some of these results.