Showing papers by "University of Science and Technology Beijing published in 1996"

Formalism of new ternary model expressed in terms of binary regular-solution type parameters

Abstract: In the previous paper, we have presented a new method for calculating ternary thermodynamic properties based on three binaries. This new model can overcome the inherent defects for both current symmetrical and asymmetrical models and can combine two kinds of current models into one. More important, it can eventually realize the computerization for calculating thermodynamic properties and phase diagrams for multicomponent systems. In this paper we will give this new model a new formalism based on binary regular-solution type parameters. When this model is applied, all we need to do is substitute these parameters into formulae presented here and evaluate them by using a simple calculator. Since a large number of real systems can be approximately fit through a regular-solution type model, therefore, this new formalism is significant.

Measurement of friction under sheet forming conditions

Abstract: Among the tests used to evaluate friction in sheet forming processes, bending-under-tension (BUT) tests have received considerable attention. A new test was developed incorporating a smooth increase of wrap angle during deformation, even at high deformation rates, thus replicating typical conditions at die radii. A corresponding data analysis procedure was introduced to separate the effects of bending and friction and to account for the strain-rate sensitivity of the test material. The new test and analytical procedure were used to investigate the frictional behavior for four sheet alloys: interstitialfree (IF) steel, high-strength galvanized (HSG) steel, 2008-T4 aluminum, and 70/30 brass. A range of testing rates, pin radii, and lubrication conditions were employed, and the variation of friction coefficient (μ) as a function of contact radius, contact angle, and punch speed was measured. Complex variations ofμ with respect to tool radius and wrap angle were observed, consistent with previous studies. No significant, systematic variation ofμ was found for punch speeds ranging from 1.7 to 170 mm/s, contrary to reports in the literature. Failures in 2008-T4 aluminum shifted from tensile localization to bending as the tool radius was reduced. The other materials consistently failed by tensile localization.

Thermodynamic evaluation of the Cu-R (R: Ce, Pr, Nd, Sm) binary systems

Abstract: The phase diagrams and thermodynamic properties of the Cu-R (R: Ce, Pr, Nd, Sm) systems are reevaluated on the basis of all available experimental data, including the enthalpies of mixing reported recently. The Redlich-Kister polynomial with two or three terms is used to describe the excess Gibbs energies of liquid phases in the Cu-R systems. All intermediate phases are treated as stoichiometric, and their Gibbs energies of formation are optimized. Based on the optimized thermodynamic parameters, phase diagrams and thermodynamic properties of the Cu-R systems are calculated and compared with the experimental results. The optimized parameters seem to be in good agreement with the experimental data and might represent the regularity and systematic variation of these systems.

The effect of cadmium on the transformation of ferrihydrite into crystalline products at pH 8

Abstract: Ferrihydrite, prepared in the presence of 0 to 20 mole % Cd in the solution, was used to study the transformation of ferrihydrite into crystalline products. The result showed that the presence of Cd strongly retards the transformation of ferrihydrite into crystalline products, suppressing the formation of goethite and leading to a product which eventually consists entirely of hematite at pH 8 and at 70 °C. The fraction of hematite in the transformation products increased with increasing level of Cd in the system. When 9 mole % Cd was present, the transformation product consisted entirely of hematite. The chemical analysis and XRD data showed that Cd was incorporated into the lattice of iron oxides, Cd-hematite and Cd-goethite being formed. The mole % Cd which replaced iron in the iron oxides increased with increasing level of Cd in the system below 9 mole % Cd. Above this value, but below 20 mole % the mole % of Cd incorporated in the lattice of iron oxides was constant at about 2.9 mole %. The volume of the unit cell of Cd-goethite increased with increasing level of Cd in the system until the goethite production was entirely suppressed. The volume of the unit cell of Cd-hematite also increased with increasing level of Cd, below 9 mole % of Cd in the system. Above this value, it was constant. Scanning electron microscopic examination showed that the presence of Cd affected the morphology of hematite more than that of goethite. The goethite grew from ferrihydrite as acicular crystals independent of the amount of Cd in the system. The shape of hematite particles varied from irregular platelets with lower Cd level, to ellipsoids, with higher Cd level in the system, and it also suggested that Cd prevented the formation of goethite by hindering the dissolution of ferrihydrite rather than by interfering with nucleation and growth of goethite from solution. The rate of transformation was studied at pH 8, 50 °C and 70 °C. The transformations were first order reactions at both temperatures.

Thermodynamic criterion for judging the symmetry of ternary systems and criterion applications

Abstract: Based on previous significant and enlightening studies in the literature and on thermodynamic considerations, a thermodynamic criterion for identifying the symmetry of ternary systems (from energy-asymmetry) is now proposed after having been successfully tested on a large number of molten salt and alloy systems. After a systematic comparison was made of calculated phase diagrams and excess thermodynamic properties with experimentally measured ones, it can be concluded that in using geometric models to predict ternary thermodynamic properties from subbinary systems, the key point is to choose a reasonable symmetric or asymmetric model noting that in most cases the main source of error in prediction arises from misjudging the asymmetric component in the asymmetric geometric model. This is of great significance in improving the calculated accuracy when predicting the thermodynamic properties of a ternary solution phase from data for the subbinary systems.

Local ordering of oxygen vacancies in cubic zirconia (ZrO2) stabilized with yttria (Y2O2) and magnesia (MgO) I. Electron diffuse scattering study

Abstract: Diffuse scattering, being highly intensive and confined in reciprocal space to a regular geometric surface exhibiting the translation symmetry of the bcc reciprocal lattice, is observed by electron diffraction from partially stabilized zirconia with Y2 O3 and MgO. This material is a structural ceramic having potential applications at high temperatures (> 1000°C). A three-dimensional geometric model of the diffuse scattering distributed in reciprocal space is constructed and an analytical equation corresponding to this model is established. In the reciprocal-space unit cell, the diffuse scattering distributes on the surfaces of eight rotational ellipsoids whose rotational axes are along the (111) directions of the bcc reciprocal lattice. Possible sources regarding the formation of the diffuse scattering are discussed. It is concluded that local ordering of oxygen vacancies in the cubic phase matrix, corresponding possibly to a transition state changing from the disordered cubic fluorite structure ...

Modification of hypoeutectic low alloy white cast irons

Abstract: In order to modify the continuous network of eutectic cementite normally found in low alloy white cast irons into a dispersive distribution, strategies of controlling the morphology of eutectic cementite by additives are discussed. Qualitative arguments are presented and applied to the development of a complex modifier REAINTi. With the addition of this modifier to low carbon white cast irons nearly one fifth of the original eutectic cementite network can be modified into blocky particles in the plane of polish, and one third into isolated irregular ones. The experimental data shows that Ti(CN) may act as an effective nucleant or a grain refiner for eutectic cementite. The modification effects of rare earth elements are attributed to their abilities to purify the melt, promote divorced eutectic growth and refine the microstructure. Aluminium contributes to the modification by its purification effect.

Electrodeposited thin oxide films

Abstract: Many oxide films such as those of most alkali earth metals, most transition metals and rare earth elements can be obtained through a new process called electrochemical deposition-pyrolysis. In the present paper the formation kinetics and mechanisms and the structure and properties of AlOOH films are discussed as an example.

Critical hydrogen concentration for hydrogen-induced cracking of type 321 stainless steel

Abstract: The effects of hydrogen concentration (CH) on ductility and fracture of type 321 (UNS S32100) stainless steel (SS) were studied. A linear relationship was obtained for CH and ductility red...

Thermodynamic reoptimization of the Ag-Sn system

Abstract: The Ag-Sn binary system is reoptimized because of the increasing interest in lead-free solder development The ordered semistoichiometric Ag3Sn phase is described as a line compound while the other phases are represented by Redlich-Kister expressions Results are compared with previous efforts, and the agreement between the calculated phase diagram and the assessed phase boundary data has been significantly improved while reproduction of experimental data for thermodynamic properties remains excellent

Combustion co-synthesis of Si3N4-based in situ composites

Abstract: The feasibility of synthesizing silicon nitride-silicon carbide-titanium carbonitride composites by combustion reactions is demonstrated. With titanium carbonitride taken to be an ideal solid solution, its composition is determined as TiC0.36N0.64. Thermodynamic analysis supports the experimental results.

Fault detection based on evolving LVQ neural networks

Abstract: This paper proposes a novel approach of employing genetic algorithms (GA) to set initial reference vectors in the Kohonen layer of learning vector quantization (LVQ) neural networks. The aim of this investigation is to improve the learning characteristics of LVQ so as to get more accurate classification results. In the proposed scheme, the reference vectors are set to the locations mostly matching the probability distribution of training vectors. Genetic algorithms are applied to optimize the locations and distribution of the reference vectors. After competitive learning of LVQ, the reference vectors are employed to be representatives of various patterns to determine the categories which testing vectors belong to a comparison study is reported based on LVQ with random initial reference vectors, LVQ with GA learning and LVQ with initial reference vectors set by GA. Experimental results of a case study have shown that the proposed method is promising for machine fault classification.

Local ordering of oxygen vacancies in cubic zirconia stabilized with yttria and magnesia II. Determination of local ordering parameters of oxygen vacancies

Abstract: Diffuse scattering produced by oxygen-vacancy local ordering in ZrO2 stabilized by Y2O3 and MgO was studied by Dai et al. in 1996 using electron diffraction. A three-dimensional geometrical model in reciprocal space was established for describing the equal intensity contours of diffuse scattering observed experimentally. In this paper, the kinematical electron diffraction theory is applied to calculate the diffuse scattering produced by oxygen vacancies. A direct relationship between the local ordering parameters and the distribution of diffuse scattering intensity is given. By assuming that the intensity profile across the maximum intensity contour, as defined by the surface of the geometrical model, is a Gaussian shape, the local ordering parameters of oxygen vacancies are determined. The parameters are then reapplied to calculate the distribution of diffuse scattering intensity, and the results show good agreement with the experimental observations. It is concluded that the oxygen vacancy-oxyg...

Partial phase diagram of the Ti-Al binary system

Abstract: The equilibrium temperature-composition coordinates of the β/(β + α), (β + α)/α,α/(α + γ), and (α γ @#@)/γ phase boundaries were determined for the binary Ti-Al phase diagram through the temperature range 1150 to 1400 °C by means of diffusion couples with subsequent EPMA examination. This was supplemented with microstructural examination of a two-phase alloy. No peritectoidal decomposition reaction of the type α→ β + γ reported by Murray [88Mur] at 1280 °C was found. Results indicate that the a phase persists to temperatures well above 1400 °C. The phase boundaries from the present work are in agreement with the Mc Cullough [88Mcc] binary phase diagram.

Microstructure and crystallographic texture of rolled polycrystalline Fe3Al

Abstract: An imperfectly B2 ordered Fe3Al aggregate was cast, thermomechanically hot rolled and finally annealed at 870 K. Subsequently, the specimen was rolled at 800–830 K to a strain e of 80%. The microstructure and the crystallographic texture of the rolled polycrystalline sample was investigated within the range e=20–80%. The microstructure consisted of flat, elongated grains. In numerous grains straight slip lines were detected. Even after e=80% recrystallization was not observed. The rolling texture of Fe3Al considerably deviates from that of non-ordered body centered cubic (b.c.c.) alloys and pure b.c.c. metals. The {111}〈uvw〉 texture fibre (7-fibre) was very pronounced, while the {hkl}〈110〉 fibre (α-fibre) was very weak. The {112}〈110〉 orientation which represents the strongest texture component in non-ordered b.c.c. alloys did not occur at all. The textures are discussed in terms of the {110}〈111〉, {112}〈111〉, {112}〈111〉 and {123}〈111〉 slip systems. The contribution of crystallographic slip of the various types of potential slip systems was simulated by means of the Taylor theory.

The genesis of Cu-bearing quartz veins by metamorphic remobilization from stratiform red bed deposits, SW County Cork, Ireland

Abstract: Polymetallicmajor veins of the West Carbery district (County Cork) are compared with the nearby stratiform-disseminated copper mineralization in metasedimentary rocks, containingminor veins (metamorphic quartz veins and veinlets) These stratiform deposits are hosted by non-marine Devonian sediments (Old Red Sandstone), metamorphosed in the Hercynian orogeny In sulphides from the stratiform deposits and minor veins, isotopic compositions of sulphur (δ34S) range from − 2100 to + 514%0, consistent with the vein sulphide being remobilized stratiform-disseminated sulphide, and the latter being of diagenetic bacteriogenic origin Sulphate (barite), found in veins separate from the sulphides, has δ34S + 123 to + 157%0 consistent with groundwater origin In minor-vein quartz, fluid inclusions have homogenization temperatures consistent with trapping under the estimated peak-metamorphic conditions (300–400°C, 1–3 kbar)