Showing papers by "University of Science and Technology Beijing published in 1993"

Design and development of hot

Abstract: As the first step to design and develop the new hot corrosion-resistant nickel-base single-crystal superalloys by thed-electrons alloy design theory (or the New PHACOMP), an evaluation of the phase stability of the modified hot corrosion-resistant IN738LC nickel-base superalloys (Ni-16Cr-9.5Al-4.0Ti-8.0-Co-0.55Nb-0.06Zr-0.05B-0.47C-(0~3)Ta-(0~3)W-(0~3)Mo (in atomic percent)) was conducted with the alloy design theory. The critical conditions for suppressing the precipitation of the brittle σ phase can be described by the electronic parameters $$\overline {Mdt} \leqslant 0.991$$ and $$\overline {Md\gamma } \leqslant 0.93$$ 0.93 which can be applied to thed-electrons alloy design of hot corrosion resistant nickel-base superalloys with high Cr contents.

Extended x-ray-absorption fine-structure study of GaAsxP1-x semiconducting random solid solutions.

Abstract: The extended x-ray-absorption fine-structure (EXAFS) technique is employed to probe the local atomic structure of the III-V pseudobinary solid solutions GaAsxP1-x as a function of the composition. The first- and second-neighbor bond lengths as well as their variation with the composition are reported. The results imply that the local atomic structure is distorted. Both first-neighbor bond lengths and cation-cation bond lengths exhibit a bimodal structure, showing a tendency to retain the values of pure compounds. Anion-anion bond lengths are much closer to those predicted by Vegard's law; however they still show a significant deviation from it. On the basis of this result, the authors propose that the atomic-scale structure of these compounds can be described by a random distribution of five special coordination tetrahedra. The relation between local atomic structure and EXAFS as well as x-ray-diffraction results is discussed.

The influence of the rolling direction on the mechanical behavior and cavity formation during superplastic deformation of 7075 A1 alloy

Abstract: The superplastic 7075A1 alloy was tested over a range of strain rates 10−2−10−4s−1 at a temperature range 430–510°C using specimens machined with the rolling direction parallel and perpendicular to the tensile axis. It is shown that the mechanical properties of the alloy, including the elongations to failure, are essentially identical. Microstructural observations show that the cavities tend to form in stringers and these stringers are always oriented along the tensile axis regardless of the rolling direction. The cavities are not nucleated primarily at large Fe-rich or Si-rich particles, nor do they grow from pre-existing microvoids which may be introduced during thermomechanical processing. The cavities are nucleated preferentially at small particles or some irregularities in the grain boundary during superplastic deformation.

Hamiltonian cycles in 3-connected claw-free graphs

Abstract: In this paper, we show that every 3-connected claw-free graph on n vertices with δ ≥ (n + 5)/5 is hamiltonian. © 1993 John Wiley & Sons, Inc.

Single-ion conduction and lithium battery application for ionomeric cross-linking polymer

Abstract: The single-Li+ conduction of the cross-linking poly [oligo (oxyethylene) methacrylate-co-lithium methacryloyl hexylsulfonate]s was studied, and an Li+ ionic transport number of 0.994 estimated from the isothermal transient ionic current (ITIC), in which an ion-blocking platinum electrode was used. The results show that Li+ -ionic conduction can be reasonably described by Vogel–Tammann–Fulcher (VTF) equation, suggesting that there is close correlation between ionic migration and segmental motion in these polymers. The battery composed of lithium/this copolymer film/polyaniline supplied a constant short circuit current (JSC) of 45 μA/cm2 and an open circuit potential (VOC) of 3.6 V at 25°C. © 1993 John Wiley & Sons, Inc.

A study of the improvement

Abstract: 1. R.D. Noebe, R.R. Bowman, and M.V. Nathal: Int. Mater. Rev., in press. 2. R.R. Bowman, R.D. Noebe, S.V. Raj, and I.E. Locci: Metall. Trans. A, 1992, vol. 23A, pp. 1493-1508. 3. J.H. Schneibel, M.G. Jenkins, and P.J. Maziasz: HighTemperature Ordered lntermetallic Alloys V, Materials Research Society Symposia Proceedings, 1. Baker, R. Darolia, J.D. Whittenberger, and M.H. Yoo, eds., Materials Research Society, Pittsburgh, PA, 1993, vol. 288, pp. 549-54. 4. C.A. Johnson: Report No. 79CRD212, General Electric Co., Schenectady, NY, December, 1979. 5. G. Quinn: J. Am. Ceram. Soc., 1990, vol. 73, pp. 2374-84. 6. E.M. Schulson and J.A. Roy: Acta Metall., 1978, w)l. 29, pp. 29-38. 7. K. Vedula, K.H. Hahn, and B. Boulogne: High-Temperature Ordered Intermetallic Alloys 111, Materials Research Society Symposia Proceedings, C.T. Liu, A.I. Taub, N.S. Stoloff, and C.C. Koch, eds., Materials Research Society, Pittsburgh, PA, 1989, vol. 133, pp. 299-304. 8. R.W. Margevicius and J.J. Lewandowski: Scro~ta Metall. Mater., 1991, vol. 25, pp. 2017-22. 9. R.D. Noebe, C.L. Culler, and R.R. Bowman: J. Mater. Res., 1992, vol. 7, pp. 605-12. 10. E.P. George and C.T. Liu: J. Mater. Res., 1990, vol. 5, pp. 754-62. I1. 1. Baker, P, Nagpal, F. Liu, and P.R. Munroe: Acta Metall. Mater., 1991, vol. 39, pp. 1637-44. A Study of the Improvement of Superplasticity of 7075 Alloy

Hydrogen-facilitated corrosion and stress corrosion cracking of austenitic stainless steel of type 310

Abstract: The effects of hydrogen precharge and stress on anodic dissolution for Type 310 austenitic stainless steel (ASS) have been investigated. An experiment determining the effect of hydrogen on stress corrosion cracking (SCC) was carried out in a boiling 42 pct MgCl2 solution and in a 2.5 mo/L H2SO4 + 1 mol/L HC1 solution. The results showed that both hydrogen and stress would increase the dissolution rate, and the effects of hydrogen and stress on the dissolution rate were synergistic rather than simply additive. Hydrogen lowered the threshold stress and the shortened fracture time of SCC in a boiling MgCl2 solution by a factor of 1/5 and 10, respectively.

Design and development of hot corrosion-resistant

Abstract: A systematic study of the effects of refractory metals Ti, Ta, and Nb on the microstructures and properties was conducted with a hot corrosion-resistant alloy system Ni-16Cr-9Al-4Co-2W-lMo-(0~4)Ti-(0~4)Ta-(0~4)Nb (in atomic percent) which was selected based on thed-electrons alloy design theory and some basic considerations in alloying features of single-crystal nickel-base superalloys The contour lines of solidification reaction temperatures and eutectic (γ + γ′) volume fraction in the Ti-Ta-Nb compositional triangle were determined by differential thermal analysis (DTA) and imaging analyzer Compared with the reference alloy IN738LC, in most of the compositional ranges studied, the designed alloys show very low amounts of eutectic (γ + γ′) (⪯04 vol pct), narrow solidification ranges (⪯65 °C), and wide “heat-treatment windows” (>100 °C) This indicates that the alloys should have the promising microstructural stability, single-crystal castability, and be easier for complete solution treatment In a wide compositional range, the designed alloys showed good hot corrosion resistance (weight loss less than 20 mg/cm2 after 24 hours kept in molten salt at 900 °C) By summarizing the results, the promising alloy compositional ranges of the alloys with balanced properties were determined for the final step of the alloy design,ie, to grow single crystal and characterize mechanical properties of the alloys selected from the previously mentioned regions

Applied stereology in materials science and engineering

Abstract: Summary A general view of the role of stereology in materials science and engineering (MSE), is followed by a discussion of applied stereology for one-, two- and multi-phase structures, and by examples of stereology applications to MSE, such as the impact of stereology on the creation and evolution of modern high–strength, low-alloy steels. The present state and prospects of applied stereology in MSE are informally discussed. It is demonstrated that, without stereology, materials science cannot evolve into a truly quantitative science, and that the needs of both materials scientists and materials engineers should be met by the continuing cooperation of those who develop stereological methods and those who apply them. To solve such problems as quantifying the interaction between features of similar and different dimensions in two- or multi-phase structures, a general parameter for volumetrical contiguity of second-phase particles, a contiguity parameter for second-phase particle profiles in grain-boundary surfaces, and techniques termed ‘reversed stereology’ are proposed and discussed.

A general model for bop decarburization

Abstract: The decarburization in the BOP (Basic Oxygen Process) has been modeled. The model was formulated based on the industrial data relating the temperature and the carbon content of the bath. Several formulae for calculating the variation of carbon and oxygen contents in the liquid metal as well as carbon monoxide composition in the gas phase were derived as a function of blow time, oxygen blow rate, gas purity and melt weight; these derivations were done for low ( 0.3%) C levels. The model was applied to a typical BOP operation and the calculated results show good agreement between predicted values and the actual operating values. It is expected that this model can be used as a reference for analyzing various steelmaking processes.

The effects of Ti3Ni4 precipitates on the R-phase transformation

Abstract: TiNi is an important alloy for its shape memory effect. It is known that both the martensite and the R-phase transformations are responsible for the shape memory effect. There are several kinds of precipitate in near equal atomic, Ni-rich TiNi alloy, amongst which Ti[sub 3]Ni[sub 4] precipitates most strongly influence the R-phase and martensite transformations. Use of constrained aging can promote the all-around shape memory effect (ARSME) because the stress fields generated by the Ti[sub 3]Ni[sub 4] precipitates is thought to introduce univariant R-phase and martensite transformation. A number of studies have been performed to understand the effects of the precipitates, but disagreement still exists. Xie et al. showed that the morphology of the R-phase is dependent on the dispersion of the precipitates. In specimens with coarse precipitates, the R-phase has a needle-like domain structure, while in specimens with fine dispersed precipitates a 'basket weave-like structure', is observed after the R-phase transition. Conversely, Nishida et al. report that the appearance of the R-phase transformation is attributable to the formation of precipitates, while the presence of precipitates and the difference in precipitate distribution does not influence the crystallographic and morphological nature of the R-phase transformation. The purpose of this work ismore » to systematically study the effect of Ti[sub 3]Ni[sub 4] precipitate on phase transformation. Here the authors report a preliminary investigation of this work.« less

Formation of NaCl-type Cr carbide by carbon ion implantation

Abstract: A new NaCl-type simple structured fcc chromium carbide was observed after 50 keV carbon-ion implantation into pure Cr thin films. The lattice constant was 0.403 nm determined by electron diffraction. TEM in situ annealing showed that the new phase was stable up to a temperature around 300°C. Auger spectra confirmed the formation of the carbide. The formation energy of the carbide calculated by Miedema's empirical method was −7 cal/mol.

Enhancements of thermal structure stability in a Ni-Base superalloy

Abstract: [gamma][double prime](bct DO[sub 22] structure) and [gamma][prime] (fcc L1[sub 2] structure) are typical strengthening phases in nickel-base superalloys. The unique strengthening effect of [gamma][double prime]-Ni[sub 3]Nb and [gamma][prime]-Ni[sub 3]Al helps Incone1718 to have wide industrial application. Because of the structure stability limitation of [gamma][double prime], the highest service temperature of IN718 is 650[degree]C. Microstructure instability of IN718 is mainly controlled by a [gamma][double prime] coarsening and plate-like [delta] phase formation. In order to improve structure stability, Cozar and Pineau published a pioneer paper on a modified alloy with a compact morphology of [gamma][double prime] and [gamma][prime], which showed higher thermal stability at age hardening test results. Recently a series of papers slightly modifying the chemical composition with variation of Al, Tk and Nb contents in IN718 has shown that a compact morphology can be obtained by appropriate heat treatments and that mechanical properties beyond 650[degree]C can be improved. However, structure stability at long time aging beyond 650[degree]C, as well as reasons to improve structure stability have scarcely been published. A detailed study in this paper was undertaken to develop a compact morphology. Cube-shaped [gamma][prime] particles were coated on their six faces with a shell of [gamma][double prime] precipitates, so amore » higher structure stability was created compared to separate precipitation of [gamma][double prime] and [gamma][prime] as the mixture of disk-shaped [gamma][double prime] and round [gamma][prime] particles in conventional IN 718. This investigation concentrates on the long time aging structure stability beyond 650[degree]C for fundamental understanding and explanation of such an improvement in thermal structure stability of compact morphology.« less

Hydrogen probe equipped with SrCeO3-based proton conductor and Ca/CaH2 reference electrode

Abstract: The protonic transference number of SrCe0.95Yb0.05O3-α (SCYB) ceramic pellets was determined to be above 0.9 in the temperature range of 873 to 1073 K using a hydrogen concentration cell. The density of the ceramic disk and tube is above 96 pct of the theoretical. Highly dense SCYB tube and glass seal improved the reliability and life of an electrochemical hydrogen probe. When the probe was immersed in molten aluminum, a hydrogen concentration cell was established as Mo, Ca/CaH2|SrCe0.95Yb0.05O3-α|[H]in molten Al, Mo The probe under different conditions generated stable electromotive force within 5 minutes after immersion and responded rapidly to the change in the atmosphere. The thermodynamic stability of the solid electrolyte under the testing conditions is also discussed.

Characteristics of heat resistant alloys Ti10Nb45Al and Ti18Nb48Al

Abstract: Based on a systematic study of the ternary Ti-Nb-Al system, two attractive heat resistant alloys, Ti10Nb45Al and Ti18Nb48Al, were developed, and the characteristics of these alloys were discussed: (1) After annealing at 1,200 C for 240 h and furnace cooling to room temperature, the Ti10Nb45Al alloy exhibits an [alpha][sub 2] + [gamma] lamellar microstructure, and the Ti18Nb48Al alloy shows a plate-like structure consisting of [alpha][sub 2], [gamma] and [gamma][sub 1] phases. (2) The specific strengths of Ti10Nb45Al and Ti18Nb48Al are much higher than TiAl and superalloys in the temperature range of 800 [approximately] 1,100 C. The compressive yield strengths of these alloys are on the order of 700 MPa at 800 C and 350 MPa at 1,100 C. The density of these alloys is about 4.3 g/cm[sup 3]. (3) The annealed Ti10Nb45Al and Ti18Nb48Al exhibit some ductility at room temperature, with the compressive elongation on the order of 12% and the fracture toughness as high as 16 MPa[radical]m. The ductile-brittle transformation temperatures for Ti10Nb45Al and Ti18Nb48Al are 650 C and 750 C, respectively. (4) The parabolic constant K[sub p] for oxidation of Ti10Nb45Al and Ti18Nb48Al are 0.88 and 0.29 mg[sup 2]cm[sup [minus]4]h[sup [minus]1] respectively, which are two orders of magnitudemore » lower than that of TiAl and Ti[sub 3]Al alloys.« less

Characterization of diffusion induced grain boundary migration in the Ag/Cu system

Abstract: The phenomenon of diffusion induced grain boundary migration (DIGM) when silver diffuses along copper's grain boundaries was confirmed through the characterization of the microstructure and the morphology of the migrated boundaries, the discontinuity and asymmetric character of the concentration profile, the dislocation configuration and the kinetics of migration by means of SEM, EPMA, TEM and AEM. The experimental results were discussed to prove the existence and the characteristics of DIGM in Ag/Cu system.

Inhomogeneity of rolling texture in Fe28Al2Cr alloy

Abstract: Inhomogeneity of rolling texture in metal sheets has been investigated, which should be avoided if the normal rolling texture is expected, or promoted if a certain special property could be thus obtained (e.g. in Fe-3%Si sheet). On the other hand, the investigation could also help in revealing the detailed deformation mechanism in metal sheets. Iron aluminides based on Fe[sub 3]Al are well known for their good oxidation resistance, excellent sulfidation resistance, low cast and lower density than stainless steel. But the knowledge of texture development and its inhomogeneity, which could affect the properties of the material, has so far been obtained less.

A new six-dimensional Burgers vector of dislocations in icosahedral quasicrystals determined by convergent-beam electron diffraction

Abstract: A new six-dimensional Burgers vector of dislocations in Al–Cu–Fe and Al–Pd–Mn icosahedral quasicrystals has been determined to be 1/2〈11 – 200 – 2〉 by means of defocused convergent-beam electron diffraction. The component of the Burgers vector in the physical space is parallel to a twofold axis with a magnitude of 0·18nm, which is about an eleventh of that in the complementary space.

A new grain-refinement process for superplasticity of high-strength 7075 aluminium alloy

Abstract: The superplasticity of high strength 7075 aluminium alloy has been improved to a great extent by the new thermomechanical treatment proposed. This treatment (TMPA) includes solution treatment, overageing, warm-rolling deformation, recrystallization and an artificial ageing process. The maximum elongation may be up to 2100% under deformation at an initial strain rate of 8.33×10−4s−1 and a temperature of 510 °C, which is much higher than reported before. Observation of the microstructure changes revealed that the excellent superplastic elongation of the alloy seems mainly to be due to a decrease in the grain growth rate of the alloy and a reduction in the number of cavities nucleated during superplastic deformation.

A cavity nucleation model during high temperature creep deformation of metals

Abstract: Based on previous theoretical models of cavity nucleation during creep deformation, a new cavity nucleation model is proposed in this paper. The basic idea of this new model is that cavity nucleation during creep deformation depends not only on the stress concentration of a piled-up group of dislocations but also vacancy clustering. The new equation for the critical radius of cavity nucleation is as follows, rc = (2γ/σ∞) − (2d/3E) σ∞ where rc is the critical radius of cavity nucleation, γ is the surface energy, σ∞ is the remote applied stress, d is the grain size and E is Young's modulus. When the applied stress is small enough, the equation can be simplified to rc = 2γ/σ∞, which was proposed by Raj et al. In the limit, when the applied stress σ∞ is large enough, the critical radius goes to zero and the upper bound stress for cavity nucleation can be obtained, which is very similar to that proposed by Smith et al.

Combustion reaction of ni40ti60 during mechanical alloying in oxygen atmosphere

Abstract: BEIJING UNIV SCI & TECHNOL,BEIJING 100083,PEOPLES R CHINA. ACAD SINICA,INST MET RES,SHENYANG 110015,PEOPLES R CHINA. RSA,ATOM IMAGING SOLIDS LAB,SHENYANG 110015,PEOPLES R CHINA. RSA,STATE KEY LAB,SHENYANG 110015,PEOPLES R CHINA.;WANG, KY (reprint author), CHINESE ACAD SCI,INST MET RES,BEIJING,PEOPLES R CHINA

Analysis of the coercive field in Sm2Fe17Nx metal-bonded material

Abstract: In the present paper the nucleation as well as the pinning fields in Sm2Fe17Nx Sn-bonded material are analysed based on the well established micromagnetic theory. The microstructural parameters derived from the measured temperature dependence of the coercive field indicate that the coercive field in Sm2Fe17Nx Sn-bonded material is dominated by the nucleation field occurring in the inhomogeneous area near the grain surface. The magnetic phase transition at the Curie temperature from the ferromagnetic to the paramagnetic state of the magnetically soft phase Sm2Fe17 existing in Sm2Fe17Nx magnets leads to a decrease of the effective demagnetization factor. Furthermore the temperature dependence of the domain wall energy γ, the average exchange constant A, the domain wall width δB, as well as the critical diameter of a single domain particle Dc.

Stable decagonal Al-Cu-Co-Si phase: A phason-perturbed quasiperiodic crystal.

Abstract: The analysis of high-resolution electron-microscopy images of the stable ${\mathrm{Al}}_{62}$${\mathrm{Cu}}_{20}$${\mathrm{Co}}_{15}$${\mathrm{Si}}_{3}$ decagonal quasicrystal shows a long-range aperiodic translation order similar to that of Penrose tiling. Thus this particular decagonal phase could be interpreted as a phason-perturbed quasiperiodic crystal.

Thermal stresses around two parallel cracks in two bonded dissimilar elastic half-planes

Abstract: Thermal stresses around two parallel cracks in two bonded dissimilar elastic half-planes are determined. One of the cracks lies in the upper half-plane, while the other is in the lower half-plane. Uniform heat flow is assumed to be at right angles to the interface. Application of the Fourier transform technique reduces the problem to that of solving dual integral equations. To solve the equations, the difference of the crack surface temperature and those of the crack surface displacements are expanded in a series of functions which are automatically zero outside the cracks. The unknown coefficients in the series are solved by the Schmidt method. The stress intensity factors are calculated numerially for composite materials featuring a ceramic upper half-plane and a steel lower half-plane.

Kinetics of Passive Film Formation on Scratched Bare Surfaces of Stainless Steels in Magnesium Chloride Solutions

Abstract: Kinetics of passive film formation on the bare surface of scratched stainless steels SS in magnesium chloride (MgCl2) solutions were studied using the rapid scratching technique under pote...