Showing papers by "University of Science and Technology Beijing published in 1997"
TL;DR: The effect of carbon addition on the microstrures and mechanical properties of TiAl intermetallic alloys has been characterized in this paper, where it is shown that carbon is not only an efficient solid solution strengthener in TiAl, but also an efficient precipitation strengthener by fine dispersion of carbide.
123 citations
TL;DR: In this article, a unified and concise solution for inverse lattice problems is presented, which uses Ramanujan's sum rule, and a uniformly sampled arithmetic Fourier transform is presented in this work.
Abstract: The present work develops a unified and concise solution for inverse lattice problems. Also, a uniformly sampled arithmetic Fourier transform is presented in this work which uses Ramanujan's sum rule.
115 citations
01 Jun 1997-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: A new solution model has been suggested, which gets rid of this traditional way and assumes that the selected binary compositions should be closely related to the system considered and is more reasonable in theoretical considerations, more reliable in practical use, and more realistic in computerization.
Abstract: During the past 3 decades, all solution models that were used to predict thermodynamic properties of a multicomponent system from binaries improperly assumed that the selected binary compositions in a model are independent of the practical system to be treated. This assumption causes problems both in symmetrical and asymmetrical models. In this article, a new solution model has been suggested, which gets rid of this traditional way and assumes that the selected binary compositions should be closely related to the system considered. After introducing a new concept, the “similarity coefficient,” the relation between the selected binary compositions and the composition of the multicomponent system is established and a new model is generated. This new generation model is more reasonable in theoretical considerations, more reliable in practical use, and more realistic in computerization for estimating thermodynamic properties and calculating phase diagrams in a multicomponent system.
93 citations
TL;DR: A new collector for bastnaesite flotation -modified hydroxamic acid (MOHA) has been developed through several years laboratory research as discussed by the authors, which has stronger collector ability and higher selectivity compared to the other commonly used collectors.
63 citations
TL;DR: In this paper, the axial grain orientation, phase spacing and elemental distribution of the Alloy rods have been investigated, and it was found that unseeded rods usually show a strong 〈112〉 orientation at higher growth rate regime.
48 citations
TL;DR: In this article, an engineering geology evaluation method based on an artificial neural network (AN 2 EGEM) is presented, which eliminates the defects of traditional evaluation methods, which rely excessively on experience and are difficult to quantify.
39 citations
TL;DR: A study of hydrogen accumulation on grain boundaries, at inclusions, and near a kneaded notch tip was conducted in this paper, showing the susceptibility for blistering and hydrogen-induced cracking.
Abstract: A study was undertaken of hydrogen accumulation on grain boundaries, at inclusions, and near a kneaded notch tip; the susceptibility for blistering; and hydrogen-induced cracking (HIC) of ...
38 citations
TL;DR: In this article, SiC particulate reinforced 6061 Al metal matrix composites were laser beam cut using a 3kW continuous wave CO2 laser and the influence of laser processing parameters such as cutting speed, laser power, and shielding gas on the quality of the cuts were investigated.
Abstract: SiC particulate reinforced 6061 Al metal matrix composites were laser beam cut using a 3kW continuous wave CO2 laser. The influence of laser processing parameters such as cutting speed, laser power, and shielding gas on the quality of the cuts were investigated. Optical microscopy, scanning electron microscopy and X-ray diffraction were used to analyse the laser treated zone. Experimental results show that 6061 Al metal matrix composites can cut be successfully using laser. A number of Al4C3/Al4SiC4 plates were formed in the heat affected zones due to a chemical reaction between Si and Al that occurred during the laser processing.
35 citations
TL;DR: In this article, the authors introduced a thermodynamic parameter, the standard free energy changes of formation of oxide, sulphide, carbide and nitride per unit volume, as a criterion for comparing the formation tendency of these compounds.
Abstract: The present paper introduces a thermodynamic parameter, the standard free energy changes of formation of oxide, sulphide, carbide and nitride per unit volume, as a criterion for comparing the formation tendency of these compounds. The diagrams for the standard free energy change of formation of common oxides, sulphides, carbides and nitrides per unit volume vs temperature have been calculated and established based on the available thermodynamic data. It is believed that these diagrams can provide better explanations to some oxidation phenomena including the effects of reactive elements on the selective oxidation of Cr2O3 and Al2O3.
31 citations
TL;DR: In this article, two non-monotone Levenberg-Marquardt algorithms for unconstrained nonlinear least-square problems with zero or small residual are presented.
Abstract: In this paper, two nonmonotone Levenberg–Marquardt algorithms for unconstrained nonlinear least-square problems with zero or small residual are presented. These algorithms allow the sequence of objective function values to be nonmonotone, which accelerates the iteration progress, especially in the case where the objective function is ill-conditioned. Some global convergence properties of the proposed algorithms are proved under mild conditions which exclude the requirement for the positive definiteness of the approximate Hessian T(x). Some stronger global convergence properties and the local superlinear convergence of the first algorithm are also proved. Finally, a set of numerical results is reported which shows that the proposed algorithms are promising and superior to the monotone Levenberg–Marquardt algorithm according to the numbers of gradient and function evaluations.
31 citations
TL;DR: In this article, the change in displacement field ahead of a loaded notch tip for a bulk specimen before and after charging with hydrogen was measured by the laser moire interferometer technique.
Abstract: The change in dislocation configuration ahead of a loaded crack tip before and after charging with hydrogen wasin situ investigated in TEM using a special constant deflection loading device. The results showed that hydrogen could facilitate dislocation emission, multiplication and motion. The change in displacement field ahead of a loaded notch tip for a bulk specimen before and after charging with hydrogen wasin situ measured by the laser moire interferometer technique. The results showed that hydrogen could enlarge the plastic zone and increase the plastic strain. Thein situ observation in TEM showed that when hydrogen-enhanced dislocation emission and motion reached a critical condition, a nanocrack of hydrogen-induced cracking (HIC) would nucleate in the dislocation-free zone (DFZ) or at the main crack tip. The reasons for hydrogen-enhanced dislocation emission, multiplication and motion, and the mechanisms of nucleation of HIC have been discussed.
TL;DR: In this article, a metal matrix composite (MMC) of 2014 aluminum alloy reinforced with 15 vol pct SiC particulate was produced by the spray-forming-deposition process.
Abstract: A metal matrix composite (MMC) of 2014 aluminum alloy reinforced with 15 vol pct SiC particulate was produced by the spray-forming-deposition process. The as-deposited preform revealed a high density and a homogeneous reinforcement distribution. Reactive products were not found on interfaces between the reinforcement and the matrix. Compared to the control alloy, the composite showed accelerated aging after solutionizing at 502 °C, while aging was retarded after solutionizing at 475 °C. Analysis indicated that the activation energy was almost the same for the aging process after different solutionizing treatments. This suggested that while the thermal barrier for the aging process was the same, other factors affecting the aging process should be considered. For example, the effective concentration of the precipitate forming elements possibly decreased after incompletely solutionizing at 475 °C. After heat treatment, the composite showed a tensile strength similar to the control alloy. The wear resistance of the composite improved considerably. The aging behavior of the composite was also studied using the nanoindentation technique. Steep gradient distribution of elastic modulus and hardness around the reinforcement SiC particulate was observed. Theoretical analysis showed that this could be attributed to the gradient distribution of precipitates, resulting from a gradient distribution of dislocation density around the SiC particulates caused by residual thermal misfit stresses.
TL;DR: In this article, three different natural graphite powders (MPG, SPG and HPG) were used to make anode films of lithium-ion batteries by rolling technique and different X-ray experiments were performed to study the mosaic distributions and coherence lengths of graphite crystallites.
TL;DR: In this paper, the authors showed that localized anodic dissolution could facilitate dislocation emission, multiplication and motion and SCC with size of nanometers would initiate in the dislocation-free zone (DFZ) or at the original crack tip after the dissolution-enhanced dislocation emissions and motion reached a critical condition.
TL;DR: In this paper, the impact-abrasion behavior of a series of low alloy white cast irons with different morphologies of eutectic carbide was investigated using a repetitive impactabrasive wear tester.
TL;DR: In this article, experiments on the extraction of sulfur from sulfides and oxy-sulfides such as FeS, MgS, CaS, BaS, RE 2 S 3 and RE 2 0 2 S (RE - rare earth metals) by hydrogen reduction were carried out at 600 - 900 °C by means of hydrogen reduction-polarographic analysis method.
Abstract: Experiments on the extraction of sulfur from the sulfides and oxy-sulfides such as FeS, MgS, CaS, BaS, RE 2 S 3 and RE 2 0 2 S (RE - rare earth metals) by hydrogen reduction were carried out at 600 - 900 °C by means of hydrogen reduction-polarographic analysis method. The reduction degree of various sulfides by H 2 at 800 °C is in decreasing order as follows: FeS > MgS ≥RE 2 S 3 > RE 2 0 2 S ≥ CaS BaS. The equilibrium constants for reaction MgS(s) = [Mg] + [S] and MgO(s) = [Mg] + [O] obtained by using vapour-liquid equilibrium method are: K MgS = 2.0.10- 4 at 1873 K, log K mgo = 1.27 - 13670/T, e o Mg = 644.5 - 1406000/T. T.
01 Dec 1997-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this paper, a model for the isothermal coarsening of secondary dendrite arms for binary alloys is proposed to correlate the secondary arm spacing to local solidification time, melting temperature of the liquid, and the properties of the solute elements in multicomponent alloys.
Abstract: Models for the isothermal coarsening of secondary dendrite arms for binary alloys are simply expanded to correlate the secondary dendrite arm spacing to local solidification time, melting temperature of the liquid, and the properties of the solute elements in multicomponent alloys. An equation is derived. Calculations using the equation show reasonable qualitative agreement with experiment.
TL;DR: Corrosive wear of a high-strength, low-alloy steel (HSLA) was examined in 0.02 mol/L sulfuric acid (H2SO4) solution at different polarized potentials and loads using apinon-disc wear devi...
Abstract: Corrosive wear of a high-strength, low-alloy steel (HSLA) was examined in 0.02 mol/L sulfuric acid (H2SO4) solution at different polarized potentials and loads using apin-on-disc wear devi...
TL;DR: In this paper, the formation of 9R structure in a hot-worked Ti-45Al-10Nb alloy with nearly fully lamellar microstructure was studied using high-resolution transmission electron microscopy.
TL;DR: In this paper, high Tb/Dy ratio alloy powders were used to improve axial 〈1 1 1〉-oriented grain-alignment in the compacts and significant magnetostrictive "stress effect" was observed in the grainaligned compacts.
TL;DR: In this paper, the reverse epsilon --> gamma transformation temperature, recovery strain and the percentage of recovery strain are related not only to the number of cycles but also to the amount of prestrains.
TL;DR: In this article, a stress-induced alpha-2 phase transformation in a hot-deformed Ti-45Al-10Nb alloy was investigated by high-resolution transmission electron microscopy (HREM).
TL;DR: Fractal growth of molybdena, iodine, and carbon during vapor-solid transformation was studied experimentally as mentioned in this paper, which revealed phenomenologically from the experimental results that microstructures of these fractal clusters depended strongly on their growth conditions.
Abstract: Fractal growth of molybdena, iodine, and carbon during vapor-solid transformation was studied experimentally. Three types of self-similar fractal clusters were observed, respectively. These clusters included two different crystalline structures, that is, single crystal and amorphous solid. The microstructure of single crystals included whiskers, ribbonlike crystals, and dendrites. The whiskers or ribbonlike crystals stacked together easily, and formed a bifurcation aggregate such as a molybdena fractal cluster. Under certain conditions, some dendrites were distorted and became branches of a network fluster. such as an iodine quasifractal cluster. The branching amorphous clusters of carbon aggregated at the edge of a glass sample after being irradiated by an electron beam. It is revealed phenomenologically from the experimental results that microstructures of these fractal clusters depended strongly on their growth conditions.
TL;DR: According to the results of physical modelling, SEM and SAM analysis of 20MnMo steel samples, internal cracks of metal parts are recoverable The motive power of the recovery is atom diffusion and migration from matrix to voids.
Abstract: According to the results of physical modelling, SEM and SAM analysis of 20MnMo steel samples, internal cracks of metal parts are recoverable The motive power of the recovery is atom diffusion and migration from matrix to voids. The recovery process consists of two steps. In the first step, the void area is filled up with a kind of metal mass, beginning from the crack tip. There are many microvoids in the mass with different microstructure from the matrix. In the second step, microvoids decrease in size and number, and the mass microstructure approaches the matrix, with the heating temperature increasing and the holding time prolonging. Recovery tests on rejected heavy forgings are successfully processed. It is believed that the recovery technique is a potential method for improving the internal quality and reducing the production loss and cost of metal products. Similar method can be used to treat other metal construction parts for rescuing them or prolonging their service life. Further research and development of recovery technique have very important theoretical and practical significance.
01 Dec 1997-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the deformation-induced α 2 → γ phase transformation nucleates either at the α 2 / γ interfaces or at the stacking faults on the basal plane of α 2 phase.
Abstract: Deformation-induced γ → α 2 and α 2 → γ phase transformations in a hot-forged Ti–45Al–10Nb alloy have been investigated by using high-resolution transmission electron microscopy (HREM). The γ → α 2 transformation is an interface-related process, which involves the emission of the interfacial superdislocations from the misoriented semi-coherent α 2 / γ interface. These superdislocations further react with each other or with the moving dislocations in γ phase and results in the formation of α 2 phase. On the other hand, the deformation-induced α 2 → γ phase transformation nucleates either at the α 2 / γ interfaces or at the stacking faults on the basal plane of α 2 phase. The growth of γ plate is accomplished by the moving of a/6 Shockley partials on alternate basal plane (0001) α 2 . The interfaces as well as the crystallographic orientation relationship between the as-cast or deformation-induced α 2 and γ phase have been analyzed. The mechanisms for the deformation-induced γ → α 2 and α 2 → γ phase transformations were also discussed.
01 Feb 1997-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this article, a new model for predicting an activity interaction coefficient and free volume theory was proposed by using Miedema's semiempirical formation enthalpy model for binary alloys, and the Toop model.
Abstract: A new model for predicting ln γ
0
and an activity interaction coefficient ɛ
i
j
has been proposed by use of free volume theory, Miedema’s semiempirical formation enthalpy model for binary alloys, and the Toop model. The results calculated are in good agreement with experimental values except for the systems which contain nitrogen and hydrogen gas elements.
TL;DR: In this paper, the effect of temperature and cooling rate on Wid-laths and IL-boundary formation was studied, and the angles between the habit plane of Wid- laths and parent lamellae were determined by a specific optical micrographic method.
TL;DR: In this paper, a transmission electron microscope investigation has been performed on the thermal instability of the nonequilibrium α 2 γ interfacial structure in a hot-forged Ti-45Al-10Nb-2.5Mn-0.05B alloy.
TL;DR: In this article, the potential energy profile along the intrinsic reaction coordinate (IRC) has been obtained at ab initio QCISD/6-31G ∗∗ //UHF/6 -31G∗ and CCSD/ 6-31 G ∗ ∗ ∼ UHF/ 6 −31G