Showing papers by "University of Science and Technology Beijing published in 1991"
TL;DR: In this paper, the authors investigated the reduction of hematite fines and magnetite concentrates containing carbon using microwave energy and found that the reduction rate was very rapid under all conditions employed.
Abstract: Reduction of hematite fines and magnetite concentrates containing carbon using microwave energy was investigated. The reduction rate was found to be very rapid under all conditions employed. The nature of the ore mineral and flux (lime and limestone) did not influence the reduction but the nature of carbon had an effect, with charcoal being superior to coke.Microwave reduction is a highly non-isothermal process and bearing this in mind, the effect of temperature on reduction was exponential. Difference between the reduction of identical samples with microwave and conventional heating (1000°C) was remarkable–in favour of microwave heating.
68 citations
TL;DR: In this paper, the effect of grain size on the plastic deformation of grains and the stress distribution in polycrystals, particularly near grain boundary, was investigated and the results indicated that the relation of the true stress and grain size is according with the well known empirical relation σ = σ 0 (ϵ) + κ(ϵ)-d − 1 2 2 and it was found that the results by computer are a complement of experimental data.
Abstract: On the basis of the data of single crystal deformation and the characteristics of polycrystal deformation, the deformation of a set of polycrystals with special orientations and special arrangement of grains were simulated in this paper to investigate the effect of grain size on the plastic deformation of grains and the stress distribution in polycrystals, particularly near grain boundary. The results obtained indicate that the relation of the true stress and grain size is according with the well known empirical relation σ = σ 0 (ϵ) + κ(ϵ)d − 1 2 and it is found that the results by computer are a complement of experimental data. The κ(ϵ) and σ0(ϵ) values, vary with the true strain. The polycrystal strengthening is mainly due to the contribution of the work hardening and the grain boundary rim (complex slip rim) which varies with gain size and true strain. The presence of grain boundary makes the stress near grain boundary markly up or down depending on orientation of grain and orientation difference between adjacent grains.
32 citations
23 citations
01 Dec 1991-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
23 citations
TL;DR: In this paper, microstructures of Ti-24A1-11Nb were solution treated in either the α2 + β or β phase field under vacuum or hydrogen gas, followed by air (AC), furnace (FC), or controlled cooling (CC), and then aged or outgassed at 800°C.
Abstract: Microstructures of Ti-24A1-11Nb were solution treated in either the α2 + β or β phase field under vacuum or hydrogen gas, followed by air (AC), furnace (FC), or controlled cooling (CC), and then aged or outgassed at 800°C. All mechanical tests were on hydrogen-free specimens. If 1147 °C β solution treatment (ST) was followed by AC, hydrogen as a temporary β stabilizer clearly decreased the size of the α2 phase and increased greatly the retained or transformed β phase content. As a result, room-temperature tensile strength, fracture strength (σF), ductility (ef), and fracture toughness(KIc) resulting from 1147 °C solution treating in hydrogen increased by 120, 100, 60, and 42 pct, respectively, as compared with that under vacuum. If β ST was followed by FC, hydrogen as a β stabilizer increased only the β phase content but did not decrease the size of α2 phase or colony; and made ultimate tensile strength (UTS), σf, ef, andKIc increase only moderately. Cooling from the α2 + β phase field (1000 °C or 1075 °C), hydrogen as a β stabilizer changed the size of transformed α2 phase and σf, ef, andKIc increased slightly. Properties were also a function of crosshead speed. For all microstructures, α2/β boundaries appeared to be effective barriers to slip and crack initiation.
23 citations
TL;DR: The elastodynamic response of a four-layered composite with an interface crack under anti-plane shear impact load is considered in this paper, where Laplace and Fourier transforms are applied to reduce this mixed boundary value problem to a Cauchy-type singular integral equation of the first kind in Laplace transform plane, which is solved numerically.
20 citations
TL;DR: In this paper, the elastic interaction energy between a screw dislocation and a point defect is given in non-local elasticity, and it is shown that the interaction energy obtained by classical elasticity is much greater than the experimental value.
Abstract: The elastic interaction energy between a screw dislocation and a point defect is given in non-local elasticity. The interaction energy has no classical singularity. The results show that the interaction energy obtained by classical elasticity is much greater (1.4 eV or so) than the experimental value. However the value obtained by non-local elasticity is in very good agreement with the experimental value (0.5 eV). It is also proved that the nonlocal interaction energy is lower when in body-centred cubiciron an interstitial carbon atom locates in the octahedral positions than in the tetrahedral positions.
Die elastische Wechselwirkungsenergie zwischen einer Schraubenversetzung und einem Punktdefekt wird mit der nichtlokalen Elastizitatstheorie berechnet. Das Resultat zeigt, das der aus der klassischen (d. h. lokalen) Theorie abgeleitete Wert der Wechselwirkungsenergie wesentlich groser (1,4 eV) als der experimentelle Wert ist (0.5 eV), der seinerseits mit dem nichtlokal berechneten gut ubereinstimmt. Es ergibt sich auch, das im raumzentrierten kubischen Eisen die Wechselwirkungsenergie niedriger ist, wenn ein Kohlenstoffatom in der Oktaederlucke, d. h. nicht in der Tetraederlucke, sitzt.
18 citations
TL;DR: In this article, the grain size dependence of intrinsic coercivity Hc of sintered Nd-Fe-B permanent magnets is investigated, and it is confirmed that small grain sizes are connected with high Hc values, and that for magnets with different grain sizes, their coercivity can be expressed by the formula μ0Hc=Ne(kμ0HA−NiIs), where HA and Is denote the magnetic anisotropy field and spontaneous magnetization of the hard magnetic Nd2Fe14B phase, respectively, and Ne a parameter inversely changing with
18 citations
TL;DR: The stacking faults formed in 4% plastically deformed Fe-35 at.c. Alloy with the B2 ordered superlattice structure have been detected by transmission electron microscopy (TEM).
Abstract: The stacking faults formed in 4% plastically deformed Fe-35 at.% Al alloy with the B2 ordered superlattice structure have been detected by transmission electron microscopy (TEM). Their crystallographic characters have been determined by use of diffraction contrast techniques in the TEM. The observed faults are compared with stacking faults in f.c.c. materials and with dislocation multipoles. A mechanism for the production of the faults is proposed.
14 citations
TL;DR: The domains and discommensurations observed in satellite reflections are interpreted as due to the ordering of Si and Al atoms in the quasilattice of the quAsicrystal.
Abstract: Domains and discommensurations have been directly observed by transmission electron microscopy in some dark-field images using certain reflections in a Mn-Si-Al octagonal quasicrystal. The invisibility and visibility of domains and discommensurations separate the diffraction spots into basic and satellite reflections. The domains and discommensurations observed in satellite reflections are interpreted as due to the ordering of Si and Al atoms in the quasilattice of the quasicrystal. A simple model which gives satisfactory agreement with the experimental results is given.
14 citations
TL;DR: An inverse theorem on an infinite sum of alternating functions is first presented in this paper, where the pairwise interaction between ions in a linear ionic chain is first solved by this theorem.
TL;DR: In this paper, the authors discussed the free energy, phase boundary friction and reversibility for thermoelastic martensitic transformations and suggested a method to obtain, quantitatively, the energy consumed for boundary friction.
Abstract: This paper is mainly to discuss the free energy, phase boundary friction and reversibility for thermoelastic martensitic transformations. A method is suggested to obtain, quantitatively, the energy consumed for boundary friction. The base for this calculation is the phenomenological theory suggested by authors before. Applications and results of the method for different data are studied. Comparison of this method with that of Ortin and Planes is discussed. The basic viewpoint in this paper is that the energy consumed for boundary friction converts totally into irreversible heat. This is different from the “entropy argument” of Ortin and Planes. The base of this argument is also reviewed.
TL;DR: In this article, the equilibrium segregation of boron at grain boundaries and the relation between grain boundary hardening and segregation in B-doped Fe−30 wt%Ni austenitic alloy were studied with the methods of microhardness measurement and Particle Tracking Autoradiography (PTA).
Abstract: The equilibrium segregation of boron at grain boundaries and the relation between grain boundary hardening and segregation in B-doped Fe−30 wt%Ni austenitic alloy were studied with the methods of microhardness measurement and Particle Tracking Autoradiography (PTA). It was found that equilibrium segregation of boron at grain boundaries appeared in the alloy as annealed between 650 and 960°C and no segregation of boron appeared above 1050°C. It could be concluded that an excess grain boundary hardening by addition of boron to the alloy was caused by the grain boundary segregation of boron.
TL;DR: In this paper, the Mossbauer spectra showed three quadrupole doublets that can be related to different Cu sites, and two doublets (B and C) were assigned with a 57 Fe probe atom on the Cu-O square planar sites of the compound with different local charge environments.
Abstract: 57 Fe Mossbauer measurements have been performed on Fe-doped samples of Bi 1.6 Pb 0.4 Sr 2 Ca 3 Cu 4- x Fe x O y ( x =0.06 and 0.08) at room temperature. The Mossbauer spectra show three quadrupole doublets that can be related to different Cu sites. Two doublets (B and C) with larger quadrupole splitting (QS) are assigned with a 57 Fe probe atom on the Cu-O square planar sites of the compound with different local charge environments. Another doublet A with smallest quadrupole splitting is associated with a Fe atom in a planar pyramid site. the doublet with smallest QS possesses relatively the smaller area indicating that the Fe atom preferentially occupies a square planar site rather than a pyramid site. To assure our assignment, we calculated the EFG (electric field gradient) on different Cu sites with the use of the point charge model and of the calculation of an effective ions valence.
TL;DR: In this article, a chromia-dispersed Co-Cr coating has been deposited by means of reactive sputtering, and the chromia dispersed coating showed a markedly increased resistance to corrosion, and a slightly decreased resistance to oxide spallation.
TL;DR: In this article, the effects of samarium content, processing factors and the strength of the measuring magnetic field on magnetic properties of Sm 2 Fe 17 N x compound powder have been studied.
TL;DR: In this paper, the inversion of the periodic potential was presented for obtaining the pseudopotential, which might be very important for electronic structure calculations, and for the other micro-structure designing.
TL;DR: In this paper, the authors report that there is a metastable γ supersatured solution phase in an RS high aluminium and titanium nickel-based superalloy, and investigate the relationship between the cooling rate and the competition of metastable α-phase with the stable NiAl β-phase.
Abstract: In this letter we report that there is metastable γ (Ni) supersatured solution phase in an RS high aluminium and titanium nickel-based superalloy, and investigate the relationship between the cooling rate and the competition of metastable γ-phase with the stable NiAl β-phase
TL;DR: In this article, a simplified solution to point contact thermo-elastohydrodynamic lubrication is presented, by simultaneously solving the energy equation and the surface temperature equation, three-dimensional temperature distributions in the contacts are obtained based on pressure and film thickness determined in calculations of isothermal elasthydrodynamic lube.
TL;DR: In this article, the authors used the phenomenological theory to obtain the free energy function as well as the friction quasi-enthalpy and friction quasientropy in SI units in a Cu-29% Zn-3% Al alloy with optical and electron microscopy.
Abstract: Thermoelastic martensitic transformation in a Cu-29% Zn-3% Al alloy has been observed with optical and electron microscopy, including 1.0–1.2 MV high-voltage transmission electron microscopy (TEM), and treated with the phenomenological theory suggested before. The observation showed that the transformation was conducted in three stages: parallel plates growing, self-accommodating variants advancing, and plates merging and/or tiny plates forming in carved-up parent phase areas. TEM showed that the martensite consisted of a huge number of packets with constant size and distinct interfaces. By using the phenomenological theory, the free-energy function as well as the friction quasi-enthalpy and friction quasi-entropy are obtained in SI units. Comparing with classical theory, the free energy can be broken into three parts: the chemical free energy, the interfacial energy and the elastic strain energy. In the range of 20–70% martensite in the alloy, the interfacial energy per unit of martensite formation is constant and the corresponding elastic strain energy is a linear function of martensite percentage. Some possible explanations for this energetics relating to the observation are given.
TL;DR: In this paper, the grain growth of thin Ni films induced by Ni+ and Mo+ implantations was investigated for various ion energies, doses and at different temperatures, and the results fit with D = cφn.
TL;DR: In this article, the effect of cooling rate on the formation of the metastable icosahedral quasicrystal phase (IQP) was investigated and it was found that IQP was sensitive to the cooling rate in a rapidly solidified alloy of a certain composition.
Abstract: The microstructure of rapidly solidified Al-8.2 at % Mn alloy was analysed by X-ray diffraction, transmission electron microscopy and energy-dispersive analysis of X-rays and the effect of cooling rate on the formation of the metastable icosahedral quasicrystal phase (IQP) was investigated. The formation of IQP was found to be sensitive to the cooling rate in a rapidly solidified alloy of a certain composition. A lower critical cooling rate at which metastable IQP starts to appear and an upper critical cooling rate at which IQP suppresses completely the stable crystalline phase exist. The fact that the amount and the manganese concentration of IQP change non-linearly with the cooling rate suggests that there is an optimum cooling rate at which both the amount of IQP and its solute concentration reach maximum values in an alloy of a certain composition.
01 Feb 1991-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this article, a new effective method with a specially designed bob for determining liquid density has been suggested, which can simplify the procedure of measurement and can also offer more precise results.
Abstract: A summary concerning the measurement of liquid density relying on the Archimedes principle has been presented, based on which a new effective method with a specially designed bob for determining liquid density has been suggested. The application of this method to ethyl alcohol solution and liquid glycerol, as well as a theoretical error analysis, shows that this new method is significant, because not only can it simplify the procedure of measurement but it can also offer more precise results. Besides, this method can further provide surface tension or contact angle simultaneously. It is expected that this new method will find its application in hightemperature melts.