Texture of primary recrystallization on nonoriented electrical steel sheet with phase transformation

The magnetic properties of nonoriented (NO) electrical steel sheet are commonly improved if the texture of their products possesses “cube texture” (e.g., {100 〈0vw〉, “goss texture”) (i.e., 110〈011〉, and less 222 texture). Industrially “cube type” has not been obtained, but “goss texture” has been. In a greater or lesser degree, {222} texture exists. To improve “goss texture” and reduce 222 texture, the grain size of the material prior to cold rolling should be larger. When the grain size before cold rolling is larger, during primary recrystallization, “goss texture” is enriched, 222 texture is decreased, and the grain grows so easily that higher induction and lower core loss can be obtained. This does not depend on the presence of phase transformation. In case of NO steel with phase transformation, heat treatment before cold rolling has been done below the austenite transition temperature (Acin1) in order to prevent the fine grain size caused by α → γ(+α) → α transformation. By using material that was heated over Acin1 and cooled with changing cooling rates, this study describes (a) the relationship between textures before cold rolling and the texture of the final product, and (b) the development of the magnetic properties.     

Initial Stages in the Metal-dusting Process on Alloy 800

The initial stages of the metal-dusting process on Alloy 800 at 620 °C were investigated by light optical microscopy, RAMAN spectroscopy, atomic-force microscopy, Auger electron spectroscopy, transmission-electron microscopy and electron back-scatter diffraction. As it turned out the incubation period for metal-dusting is characterized by simultaneous formation of a heterogeneously growing oxide scale and deposition of carbon. The material surface shows different tarnish colors depending on the substrate-grain orientation with different susceptibility to the beginning of metal-dusting attack. “Low-index” grains were not attacked within the times investigated while the other grain orientations showed pitting. Carbon is evidently incorporated into the oxide scale from the very beginning of exposure with different intensities depending on the underlying substrate-grain orientation leading to differences in the tarnish colors. As a consequence carbides are formed even underneath “dense” oxide layers. Evidently metal-dusting attack starts at positions of the oxide scale where “higher carbon concentrations” are present.     

On the choice of “Geometric” thermodynamic models

A number of “geometric” models have been proposed for estimating the thermodynamic properties of a ternary solution from optimized data for its binary subsystems. Among the most common of these are the Kohler, Muggianu, Kohler/Toop, and Muggianu/Toop models. The latter two are “asymmetric” models in that one component is singled out and treated differently, whereas the first two models are “symmetric.” It is shown that the use of a symmetric model when an asymmetric model is more appropriate can often give rise to large errors. Equations are proposed for extending the symmetric/asymmetric dichotomy into N-component systems (N=3), while still permitting the flexibility to choose either a symmetric or an asymmetric model for any ternary subsystem. An improved general functional form for “ternary terms” in the excess Gibbs energy expression is also proposed. These terms are related to the effect of a third component upon the binary pair interaction energies. All the above considerations also apply when short-range ordering is taken into account by using the modified quasichemical model. Finally, some arguments in favor of the Kohler model over the Muggianu model are presented.     

Rhenium reduction—alloy design using an economically strategic element

A new single-crystal nickel-based superalloy has been developed as part of the GE Aviation strategy of “Rhenium Reduction” This new material provides second-generation properties while using significantly less rhenium. The new alloy development and introduction is part of the four-part strategy of “revert, recycle, recover, and reduce.”     

Models of the surface of aluminum mirrors bombarded by ions from a deuterium plasma

Changes in the optical properties of samples of aluminum-alloy mirrors caused by ion bombardment with ions from a deuterium plasma, which imitates conditions that can exist upon the operation of the first mirrors for diagnostics of plasma in an ITER, have been investigated. The basic methods of studying the mirror surfaces were ellipsometry and reflectometry; as an additional procedure, Auger electron spectroscopy was used. It has been found that the coefficient of reflection of mirrors decreases as a result of irradiation by ions with an energy of ∼1 keV, but it can be restored by the subsequent irradiation by ions with a lower energy (∼60 eV). The complex of experimental studies that were performed was used as a base for the selection of a mathematical model for a correct interpretation of ellipsometric data. The results of multiple-angle and spectral ellipsometry were analyzed in terms of the models of a clean surface and single-layer films. On the basis of the analysis of experimental data and simulation of the effective medium, we proposed a mechanism, which explains the results of the experiment; this mechanism is based on (1) the chemical processes in the surface layer in the first cycle of “degradation-restoration” and (2) the development of roughness as a result of a sequence of procedures of “degradation-restoration.”     

Crust and alumina powder dissolution in aluminum smelting electrolytes

Modern smelter potlines often undergo process excursions, which are attributed to “solubility problems” of the alumina used. Assigning the problem to a specific property is, however, a challenge, compounded by the fact that the alumina has usually undergone secondary treatments through a dry scrubbing system prior to arrival at the cell. With a better understanding there is the potential for avoiding some of the troubles experienced in these “alumina solubility” problems but there is a need to clarify what are the relevant chemical and physical properties of the alumina that are having the impact. Published and unpublished data are drawn together here to provide further insight into the alumina solubility issues.     

Microstructure and abrasion resistance of plasma sprayed titania coatings

Agglomerated titania nanopowder and a “classical” titania were sprayed by the high throughput water-stabilized plasma (WSP) and thoroughly compared. Optical microscopy with image analysis as well as mercury intrusion porosimetry were used for quantification of porosity. Results indicate that the “nano” coatings in general exhibit finer pores than coatings of the “conventional” micron-sized powders. Mechanical properties such as Vickers microhardness and slurry abrasion response were measured and linked to the structural investigation. Impact of the variation in the slurry composition on wear resistance of tested coatings and on character of the wear damage is discussed. The overall results, however, suggest that the “nano” coatings properties are better only for carefully selected sets of spraying parameters, which seem to have a very important impact. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Measurement and analysis of adhesion strength for thermally sprayed coatings

Thermally sprayed coatings have a distinctive microstructure which can be described as “a three dimensional layered structure of discs which are interlaced to form a material of composite nature.≓ The coatings are normally greater than 25 (Ώm in thickness and can thus be described as bulk coatings. The minimum microstructural detail would be a single splat (ofter described as a lamella) which is about S (Ώm (approximately 0.0002 in.) in thickness and up to 80 Ώm (approximately 0.003 in.) in diameter. This paper focuses on methods used to define and measure the adhesion of coatings or deposits formed by thermal spray technology. The properties distinguished include strength and toughness. Measurements such as the tensile adhesion test (according to ASTM C633), the double cantilever beam test, and the scratch test are detailed to illustrate their relevance to present industrial practice. Acoustic emission studies have also been used to assess the “crack density function,” a product of the number of cracks and crack size. Indentation techniques have been used to determine the fracture toughness of coatings and to demonstrate that the material properties of coatings are anisotropic. These techniques, among others, may be used to gain a fundamental understanding of coating performance or for quality control. A further focus of this paper concerns the highly variable nature of the material properties of coatings. Such variation leads to poor reproducibility during service and can cause unpredictable performance. Therefore, a section is presented on the statistical analysis of thermal spray coatings, with particular reference to the Weibull distribution. Based on “Measurement of Adhesion for Thermally Sprayed Material,”Journal of Adhesion Science and Technology.     

A scenario of development of low-voltage “underwater” discharge

Based on the analysis of experimentally obtained oscillograms of the current, voltage, and “end face” discharge spectral line intensity, a scenario of “underwater” discharge development is proposed. The three main stages of the discharge formation are revealed: the bubble growth, the “quiet” discharge, and the active discharge form differing from the previous forms by the sharp pulse intensity and greater amplitude of the voltage variation.     

Electromagnetic generation of acoustic waves near second-order magnetic phase transitions of the “order-disorder” and “order-order” type

In this work, we theoretically and experimentally established the common feature of the evolution of the efficiency of the electromagnetic generation of acoustic waves near the temperatures of second-order magnetic phase transitions characteristic of both the “order-disorder” (Curie point in isotropic ferromagnets) and “order-order” (easy-axis-angular-phase and angular-phase-easy-plane) transitions in uniaxial magnets, which consists in the fact that the peak of efficiency corresponds precisely to these temperatures at any values of the magnetic field even if in a magnetic field these temperatures cease to be the points of phase transitions.     

Investigation of the structure of compacts and sheets of an Al-Cu-Li alloy strengthened by Al<Subscript>2</Subscript>CuLi (T<Subscript>1</Subscript>) particles

X-ray diffraction and electron microscopy have been used to investigate structural states of the material of compacts and sheets of an aluminum-copper-lithium alloy with a lithium content corresponding to the field of equilibrium of a solid solution with the phase T ₁ (Al₂CuLi). In pressed strips, there arises a multicomponent texture (Bs “110”〈112〉, Cu “211”〈111〉, S “123”〈hkl〉) typical of pressed articles of aluminum-lithium alloys. Their microstructure was characterized by the presence of slip bands oriented in the rolling direction. The formation of lamellar precipitates of the T ₁ phase at slip-band boundaries in the process of deformation is supposedly stimulated by Shockley partial dislocations. In hot-rolled sheets, there arose an unusually intense nearly single-component texture of the Ex ₁ “011”〈111〉 type, whose appearance is mainly caused by the cross rolling of the sheets. The reduced strength characteristics of the sheets examined are connected with a sharply oriented character of the structure of both the matrix phase and the strengthening T ₁ phase. A quasicrystalline phase T ₂ present in the material and the precipitates of the δ′ phase exert no marked effect on the level of mechanical properties.     

A concept for the EQ coating system for nickel-based superalloys

Nickel-based single-crystal superalloys with high concentrations of refractory elements are prone to generate a diffusion layer called a secondary reaction zone (SRZ) beneath their bond coating during long exposure to high temperatures. The SRZ causes a reduction of the load-bearing cross section and it is detrimental to the creep properties of thin-walled turbine airfoils. In this study, a new bond coat system, “EQ coating,” which is thermodynamically stable and suppresses SRZ has been proposed. Diffusion couples of coating materials and substrate alloys were made and heat treated at 1,100°C for 300 h and 1,000 h. Cyclic oxidation examinations were carried out at 1,100°C in air and the oxidation properties of EQ coating materials were discussed. High-velocity frame-sprayed EQ coatings designed for second-generation nickel-based superalloys were deposited on fourth-and fifth-generation nickel-based superalloys, and the stability of the microstructure at the interface and creep property of the coating system were investigated.     

Effects of texture on the etching property of Fe-36%Ni invar sheets

In order to make a high quality color cathode ray tube, the influence of the texture on the etching property of an invar (Fe-36%Ni) shadow mask sheet has been studied. For the etching property, new values (g_R-, a_R-value) are presented which are estimated with the intensity of the inverse pole figure for the normal direction of the sheet. Furthermore, for the decision of the etching property, RD-values which are calculated with ODF are suggested. A good etching property is obtained when the RD-value is more than 2. This article is based on a presentation made in the symposium “ ’ 99 International Symposium on Textures of Materials”, held at Sunchon National University, Sunchon, Korea, April 21 ~ 22, 1999 under the auspices of The Korean Institute of Metals and Materials and the Research and Development Center for Automobile Parts and Materials.     

Preparation and Oxidation of Novel Electrodeposited Cu–Ni–Cr Nanocomposites

The poor oxidation resistance of Cu-base alloys limits their applications at high temperatures, and it cannot be improved by conventional Cr alloying because that requires an extremely high Cr content. In this work a chromia scale has been formed on novel Cu-base nanocomposites which contain much less chromium. Cu–Ni–Cr nanocomposites, with the weight percentage ratio of Cu/Ni ≈1 and various amounts of Cr, were produced by co-electrodeposition of Cu–Ni alloy with Cr nanoparticles which subsequently acted as “seeds” for chromia formation. The results of oxidation tests in air at 800°C showed that only 15 wt.% Cr in the nanocomposite was required to form an external chromia scale. Furthermore, the scale consisted only of chromia rather than the duplex scales which form on the conventional alloy even when it contains significantly more chromium.     

Surface free energy and surface stress as elastic components of the surface tension of condensed matter

The “surface free energy” and “surface stress” are basic notions in the current theory of the surface tension of solids; they were used online together or separately thousands times, but never “as elastic components of surface tension”. Most of experts highlight that these different notions cannot be mixed or confused since the first one is of the “plastic” and second is of “elastic” nature. Below these opinions are shown to be incorrect. Sufficient evidences, both theoretical and experimental, demonstrate the elastic nature of both the “surface energy” and “surface stress”. In this way, we considered the most convincible models of the metal surface based on the Coulomb interaction and purely elastic surface deformation. The reminiscent of the cantilever-beam-technique data and electrocapillary curves of mercury in combination with the specific adsorption data has logically led to the formulation of the “optimum surface electron density” notion (for the first time in the field of surface tension).     

Stability of composite materials NiAl-refractory metal with cellular structure

The structure and mechanical properties of NiAl-Wand NiAl-W-Mo composite materials (CM) obtained by sintering from powders are studied. Comparative analysis of the effect of hot compressive deformation of a compact material at 1000–1300°C on the integrity of the microspecimens and of the tungsten shells on NiAl granules in CM with cellular structure is performed. The thermokinetic stability of the grain structure of unalloyed nickel aluminide NiAl and of a NiAl-W composite material with cellular structure is investigated. The temperature of the beginning of recrystallization of the NiAl intermetallic is determined. A map of structural states is plotted in the “temperature-operating time” coordinates for CM with cellular structure. The local chemical composition of the “NiAl-refractory metal” phase boundary is studied in CM with cellular structure and without it. The effect of the structural state of CM on the yield strength in compressive tests at 1000°C is determined. The oxidation resistance at 1000–1300°C is studied and a treatment approaching the oxidation resistance of CM with cellular structure at 1000–1300°C to the level of high-temperature strength of unalloyed NiAl and of its alloy with 4 wt.% Hf is suggested. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 25–30, June, 2006.     

Materials “alchemy”: Shape-preserving chemical transformation of micro-to-macroscopic 3-D structures

The scalable fabrication of nano-structured materials with complex morphologies and tailorable chemistries remains a significant challenge. One strategy for such synthesis consists of the generation of a solid structure with a desired morphology (a “preform”), followed by reactive conversion of the preform into a new chemistry. Several gas/solid and liquid/solid reaction processes that are capable of such chemical conversion into new micro-to-nano-structured materials, while preserving the macroscopic-to-microscopic preform morphologies, are described in this overview. Such shape-preserving chemical transformation of one material into another could be considered a modern type of materials “alchemy.”     

Dependence of the thermal conductivity of alloys of the Al−Mg system on the composition and temperature

It is a common practice to study the dependencies of the physical properties of alloys on the temperature and the composition without generalizing the results. It is more logical to study these dependences complexly, i.e., as fragments of “composition-temperature-property” diagrams (whole diagrams in the ideal case). Today’s mathematical and computer possibilities provide processing of the dependences of any property on the temperature and the composition even for multicomponent systems. Mathematical analogs replace the “composition— property” graphical diagrams. The present work generalizes data on the thermal conductivity of 11 alloys of the Al−Mg system that contain 1 to 14% Mg in the temperature range of 20–350°C. The results are obtained in the form of a single regression equation that describes the data on the thermal conductivity within the range 86–190 W/(m·K) with a standard deviation of 0.7%. The choice of the regression equation is based on the existence of an analogy between heat transfer and electric transfer in metallic systems and on dependences of the electrical resistivity on the temperature and the concentration of the alloying elements known from solid-state physics. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 13–15, June, 1998.     

On some special features of the structure and properties of metallic “thin” films

Conclusions  

Mechanical response of metallic glasses: Insights from in-situ high energy X-ray diffraction

The term “metallic glass” usually refers to a metallic alloy rapidly quenched in order to “freeze” its structure from the liquid state. A metallic glass is a metastable alloy, which lacks the symmetry typical for crystalline materials and at room temperature shows an amorphous liquid-like structure. Bulk metallic glasses (BMGs) represent a class of amorphous alloys. The most notable property of BMGs is their ultrahigh (near theoretical) strength and hardness. Because the known BMGs usually miss tensile plasticity and thus exhibit catastrophic failure upon tension it is important to understand deformation mechanisms involved and thus improve their performance. This aricle analyzes the use of synchrotron radiation for evaluating the elastic-plastic response of such materials.