Gradient state of the surface layers of iron and nickel after electro-explosive alloying

Light microscopy, x-ray phase analysis, and scanning and transmission electron microscopy were used to study the structural-phase states of the regions created by the electro-explosive boriding of nickel and the boron carbiding of iron and nickel. Alloying of the surface of tool steel Kh12 with gadolinium and boron was also examined. It was found that several layers with distinctive features are formed, these layers being arranged in a regular pattern through the depth of the alloying zone: a near-surface nano-composite layer composed of synthesized phases; an intermediate layer characterized by cellular crystallization; a boundary layer with a granular structure; a fine nanocrystalline sublayer at the interface between the alloying zone and the base; a heat-affected zone with a high dislocation density. The properties of the surface of steel Kh12 after treatment were studied by measuring microhardness, wear resistance, and resistance to high-temperature oxidation in atmospheric air. An analysis was made of the convective processes that are responsible for mass transfer of the alloying elements in the surface layers during the treatment. __________ Translated from Metallurg, No. 3, pp. 52–57, March, 2007.     

Features of structure formation of the surface layer in the course of electroexplosive alloying tungsten carbide hard alloy

The surface of the VK10KS hard alloy is hardened to 25 GPa; it is affected by pulsed plasma jets formed by the electric explosion of coal-graphite fibers and aluminum or titanium foil. It is established that intense hardening is inherent in alloys after electroexplosive alloying with titanium due to the formation of TiC and (Ti, W)C carbides in the surface layer.     

Deposition of iron,nickel and iron-nickel layers from carbonyl vapors

The rate of deposition of iron, nickel and iron-nickel layers from carbonyl vapors is shown to be controlled by diffusion across the gas phase boundary layer in contact with the heated substrate. At a constant flow rate the rate of deposition is shown to increase with increase in temperature up to a critical value above which the rate of deposition either remains constant (for high flow rates) or decreases (for low flow rates). This behavior is explained in terms of the thermal convection contribution to mass transfer in the reaction system. It is shown that the composition of alloy films produced from carbonyl mixtures at temperatures greater than 200°C (473 K) can be predicted to be approximately equal to the molar ratios of iron and nickel in the vapor phase when the carbonyls alone constitute the vapor phase. These predictions cannot be extended to situations where high dilution of the carbonyls in another gas is used, or to deposition temperatures of less than 200°C (473 K).     

Increasing the wear resistance of surface layers of high-speed steel by electric-spark alloying and laser treatment

How the combined action of high-energy spark alloying and laser treatment affect the wear resistance of high-speed steel cutting tools has been studied. That action has been found to form a strengthened layer of composite refractory compounds on the tool surface, thus making it hard and wear-resistant, and create a protective barrier that reduces the adhesive interaction of the cutting tool with a chip. The tribological properties and the durability of the cutting tool can be enhanced by alloying the surface layer with elements and compounds that form stable oxides tightly bonded to the substrate. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7–8(408), pp. 44–51, July–August, 1999.     

Systematic of the equivalent influence of alloying elements on the nitrogen and hydrogen solubility in iron,cobalt, and nickel base alloys

Starting with the demonstration of the equivalent behaviour of solutes in case of the solubility and the activity of nitrogen and hydrogen in iron, cobalt and nickel base ternary and multicomponent melts, it has been shown that the equivalence principle, which was proved for the solvents iron, cobalt and nickel earlier on, is also valid among these solvents. Therefore, common reference functions have to be introduced for the evaluation of the solubility of nitrogen and hydrogen respectively. The influence of the solutes on the solubility of gaseous components nitrogen and hydrogen is uniformly graduated in the three solvents iron, cobalt and nickel. That means there must exist a valid common basic systematic. The different courses of the isothermal saturation curves can be explained by different miscibility in the liquid and the solid state of the metallic components solvent and solute as well. Based on this systematic background, it can be shown that the relation between the ordinal numbers of the solutes and their equivalence factors is directly linear within the individual element groups.     

铸铁轧辊激光合金化

在轧辊表面通过添加强碳化物形成元素,在适当的激光照射工艺条件下原位生成陶瓷相,得到以亚共晶组织为基,密集分布微米级陶瓷颗粒,同时保留较高残余奥氏体,形成强韧相间的激光合金化区.控制合金过程残余奥氏体量,可防止微裂纹的产生,在使用过程阻止裂纹的扩展.经过表层激光合金化处理的铸铁轧辊,过钢量可提高一倍以上.     

Composition control in laser surface alloying

Laser surface alloying, a process of growing interest for local surface modification, relies upon a suitable composition and microstructure for satisfactory on-the-job performance. This paper reports the results of an initial systematic study of laser surface alloying nickel onto AISI 1020 steel substrates using a statistical experimental design technique. The objective was to relate processing conditions to dimensions, solute content, and microstructural refinement of the laser alloyed zones. Solute content was of principal concern as it is the single most important factor affecting the properties of laser surface alloys. The effects of varying the laser power, beam diameter, and speed on the width, depth, nickel content, and fluctuations in nickel content are reported. Interactions between process parameters are discussed, the reproducibility assessed, contour plots for solute content drawn. Dimensionless plots are developed that relate average solute content and microstructural refinement to process parameters. Previously published data for alloying chromium into 1018 steels are shown to contain similar trends. It is felt that such an approach would facilitate selection of processing conditions to obtain reproducibly the compositions and microstructures necessary for gainful utilization of laser surface alloys.     

Physicochemical laws of the interaction of nickel aluminides with alloying elements: II. Interaction of nickel aluminides with alloying elements and/or interstitial phases

The Ni-Al-X (X is an interstitial element or phase) phase diagrams are analyzed to reveal systems that can be used as the basis for designing promising alloys and natural composites based on nickel aluminides reinforced by interstitial phases (natural composites I). The most thermally stable materials are shown to be heterophase alloys and composite materials (CMs) located in the eutectic-type (including degenerate eutectic) pseudobinary sections of ternary or multicomponent phase diagrams. They exhibit insignificant (or zero) dissolution of interstitial phases at operating temperatures and the absence of an intense interaction between CM components (natural composites II). Natural composites I based on the NiAl-or Ni₃Al-interstitial phase alloys produced upon cooling from a melt can be reinforced by the refractory thermally stable rigid interstitial phases, namely, borides and carbides, that are present in pseudobinary sections in equilibrium with these nickel aluminides, since the elements forming these phases dissolve completely in matrix melts and the mutual solubility of these phases in the solid state is low. Such borides are TiB₂ and HfB₂ in equilibrium with β-NiAl, and such carbides are, e.g., TiC and HfC in equilibrium with β-NiAl and La₂C₃, NbC, and TaC in equilibrium with γ′-Ni₃Al. Natural composites II should be produced using solid-phase methods (NiAl with AlN, Y₂O₃, Al₂O₃) or a combination of methods, where a refractory interstitial phase of the Al₂O₃ or Y₂O₃ type is solid and the intermetallic NiAl or Ni₃Al matrix is liquid. NiAl-TiB₂ (HfB₂), NiAl-Al₂O₃ (Y₂O₃), and Ni₃Al-La₂C₃ (NbC, TaC) composites are considered as examples.     

Morphological evolution during the early stages of aluminide coating growth on a single-crystal nickel superalloy surface

The (100) surface of a single-crystal Ni alloy was aluminized as a function of time to study the development of the resulting coating microstructure. A chemical vapor deposition (CVD) reactor, which was specially configured for short-term aluminizing experiments, was used to prepare coating specimens at 1150 °C. After 5 minutes, γ′-Ni₃Al particles ∼100 nm in size randomly nucleated on the alloy surface. Within 20 minutes, a coating layer consisting of preferentially oriented, columnar β-NiAl grains was formed with the segregation of refractory elements (i.e., Ta and W) from the alloy to the coating grain boundaries. The lateral growth of the columnar grains was observed to be relatively rapid for up to 45 minutes, but slowed considerably between 45 and 180 minutes. While the columnar nature of the coating did not change significantly after 20 minutes, the surface features continually evolved, with the appearance of a small amount of the γ′ phase, which coincided with the segregation of the refractory elements to the coating surface.     

Composition and thermodynamics of the surface layer of binary melts based on iron,cobalt, and nickel

The composition, thickness, thermodynamic activities of components, Gibbs energy and excess energy of formation of the surface layer on binary melts of iron, cobalt and nickel-based alloys with different interatomic interactions were evaluated with the aid of data from the literature and the authors measurements of the concentration dependence of the surface tension and molar volume.     

Morphological features of the entorhinal-hippocampal connection

The goal of this review in an overview of the structural elements of the entorhinal-hippocampal connection. The development of the dendrites of hippocampal neurons will be outlined in relation to afferent pathway specificity and the mature dendritic structure compared. Interneurons will be contrasted to pyramidal cells in terms of processing of physiological signals and convergence and divergence in control of hippocampal circuits. Mechanisms of axonal guidance and target recognition, target structures, the involvement of receptor distribution on hippocampal dendrites and the involvement of non-neuronal cellular elements in the establishment of specific connections will be presented. Mechanisms relevant for the maintenance of shape and morphological specializations of hippocampal dendrites will be reviewed. One of the significant contexts in which to view these structural elements is the degree of plasticity in which they participate, during development and origination of dendrites, mature synaptic plasticity and after lesions, when the cells must continue to maintain and reconstitute function, to remain part of the circuitry in the hippocampus. This review will be presented in four main sections: (1) interneurons-development, role in synchronizing influence and hippocampal network functioning; (2) principal cells in CA1, CA3 and dentate gyrus regions-their development, function in terms of synaptic integration, differentiating structure and alterations with lesions; (3) glia and glia/neuronal interactions-response to lesions and developmental guidance mechanisms; and (4) network and circuit aspects of hippocampal morphology and functioning. Finally, the interwoven role of these various elements participating in hippocampal network function will be discussed.     

Suitability of nickel as alloying element in titanium sintered in solid state

Abstract

The suitability of nickel as an alloying element in titanium alloys produced using the blended elemental powder metallurgy approach has been explored. Nickel initially accelerates sintering, providing greater densification at lower temperature than observed for unalloyed titanium. However, it provides only a minor improvement in the density achieved after long sintering times or at high solid state sintering temperatures. Swelling is observed under liquid phase sintering conditions. The highest density was achieved by sintering at just below the solidus temperature. Nickel also accelerates the Ostwald ripening of the pore structure and the conversion of open porosity into closed porosity.     

搅拌形式对硫酸镍结晶效果的影响

研究了锚式搅拌器和螺带式搅拌器的搅拌特点,分析了两种搅拌器对硫酸镍结晶过程的影响.实践表明,采用螺带式搅拌器可以提高结晶率,改善结晶体物理形貌,提高硫酸镍成品的产量和质量.