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13. Radiation-induced grain boundary segregation in dilute alloys

Author

Song, Shenhua

Subjects
669, Metallurgy & metallography
Abstract

Modelling of irradiation-induced segregation or thermal non-equilibrium segregation needs data on the impurity-point defect binding energy. These values are generally unavailable. In this work, an initial approach to determining impurityinterstitial binding energies in metals is established with some success on the basis of strain field arguments and the earlier work is slightly modified for more accurate calculations of oversized impurity-vacancy binding energies. The method is applied to predictions of various impurity-point defect binding energies in several transition metal matrices. With the aid of the predictions, some experimental results on radiation-induced segregation are reasonably satisfactorily interpreted. A radiation-induced grain boundary segregation (RIS) model is established for dilute alloys based on the complex mechanism and combined with McLean's equilibrium segregation model. In the model, radiation-enhanced solute diffusion is taken into consideration. Theoretical predictions are made for segregation of phosphorus in the neutron-irradiated a-Fe matrix. There exists a segregation transition temperature below which combined radiation-induced non-equilibrium and radiation-enhanced equilibrium segregation is dominant, and above which thermal equilibrium segregation is dominant; peaks in the temperature dependence of segregation shift to lower temperatures with decreasing neutron dose rate and/or increasing neutron dose; the combined radiation-induced non-equilibrium and radiation-enhanced equilibrium peak segregation temperature and the thermal equilibrium peak segregation temperature are about 150 and 550°C, respectively, for phosphorus grain boundary segregation in the a-Fe matrix at neutron dose rate = 10-6 dpa/s and neutron dose = I dpa . Grain boundary segregation of solutes in the neutron-irradiated and unirradiated (thermally aged) 2.25Cr1Mo steels doped with P and Sn is examined by means of field emission gun scanning transmission electron microscopy (FEGSTEM) which has very high spatial resolution (- 1 nm). The material is irradiated to a dose of 0.042 dpa at a dose rate of 1.05 x 10-8 dpa/s in a swimming pool-type light-water research reactor in the Paul Scherrer Institute (PSI) of Switzerland. Grain boundary microanalysis is performed in the Nuclear Electric Berkeley Technology Centre of the UK. Comparison of the experimental and predicted results shows that the predictions are generally consistent with the observations.

Published
1995

44. Combined equilibrium and non-equilibrium segregation mechanism of temper embrittlement

Author

Song Shenhua and Xu Tingdong

Subjects
Materials science, Materials processing, Mechanics of Materials, Mechanism (philosophy), Mechanical Engineering, Metallurgy, General Materials Science, Grain boundary, Tempering, Embrittlement
Abstract

Grain boundary segregation of impurities like P, S, Sb, and others is the origin of temper embrittlement of low-alloy steels. Till now it has been assumed that the segregation is determined by an equilibrium segregation mechanism, but some open questions cannot be satisfactorily explained by the equilibrium segregation mechanism. In the present work, a combined equilibrium and non-equilibrium segregation mechanism of temper embrittlement was established and some open questions on temper embrittlement were addressed by means of the model. The model was applied to phosphorus segregation in an Fe-0.3% C-3.5% Ni-1.7% Cr-0.06% P steel.

Published
1994

45. Effect of boron on corrosion resistance of Al-2.5 wt% Cu allov

Author

Yuan Zhexi, Xu Tingdong, and Song Shenhua

Subjects
inorganic chemicals, Materials science, Precipitation (chemistry), Mechanical Engineering, Doping, Alloy, Metallurgy, technology, industry, and agriculture, chemistry.chemical_element, engineering.material, equipment and supplies, Corrosion, chemistry, Mechanics of Materials, Transmission electron microscopy, Phase (matter), engineering, General Materials Science, Grain boundary, Boron
Abstract

The effect of boron on the corrosion resistance of AI-2.5 wt% Cu alloy has been investigated with transmission electron microscopy and particle tracking autoradiography. It is shown that when AI-2.5 wt% Cu alloys are doped with 0.002, 0.004, and 0.006 wt% B, the corrosion resistance of the alloys can be greatly increased. The mechanism for boron to increase the corrosion resistance is that boron addition eliminates the preferential precipitation of a second phase at grain boundaries of the alloys. Moreover, it is shown that the segregation of boron to grain boundaries is importantly responsible for the increase of the corrosion resistance of the alloys. Received 25 October 1990 and accepted 25 March 1991

Published
1992

46. Two types of boron segregation at austenite grain boundaries and their mutual relation

Author

Song Shenhua, Yu Zongsen, Xu Tingdong, and Yuan Zhexi

Subjects
Austenite, Materials science, Precipitation (chemistry), Mechanical Engineering, Transition temperature, Metallurgy, Alloy, Thermodynamics, chemistry.chemical_element, engineering.material, BORO, chemistry.chemical_compound, chemistry, Mechanics of Materials, Boride, engineering, General Materials Science, Grain boundary, Boron
Abstract

The distribution of boron in 10 p.p.m. B-doped Fe-30 wt% Ni austenitic alloy was investigated by means of particle tracking autoradiography (PTA). It was shown that when quenched from a certain temperature between 750° C and 1220° C with medium cooling rates, both equilibrium and non-equilibrium grain boundary segregation of boron appeared in the alloy. The degree of segregation represented the sum of the two kinds of segregation of boron. A transition temperature, of approximately 950° C, was found below which the equilibrium grain-boundary segregation was dominant and above which the non-equilibrium grainboundary segregation was dominant. For the degree of segregation achieved by these two types of segregation of boron there exists a temperature from 1000° C to 1050° C at which a minimum amount of segregation is obtained. It was also shown that non-equilibrium segregation of boron can considerably promote the precipitation of boride at grain boundaries.

Published
1990

48. Ionic liquid incorporated biodegradable gel polymer electrolyte for lithium ion battery applications.

Author

Ravi, M., Song, Shenhua, Wang, Jingwei, Wang, Ting, and Nadimicherla, Reddeppa

Subjects
LITHIUM ions, POLYELECTROLYTES, IONIC liquids, TETRAFLUOROBORATES, X-ray spectra
Abstract

Lithium ion conducting biodegradable gel polymer electrolytes based on a poly (ε-caprolactone):lithium tetrafluoroborate (PCL:LiBF) system doped with various concentrations of 1-Ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF) ionic liquid were prepared by solution cast technique. The gel polymer electrolyte was eco-friendly, flexible, transparent and free-standing. The conductivity and transference number measurements were carried out to investigate ionic conduction and charge transport in the gel polymer electrolytes. The frequency-dependent conductivity results revealed that the room-temperature electrical conductivity increased with increasing EMIMBF concentration. At room temperature, the gel polymer electrolyte with a composition of 85PCL:15LiBF + 40EMIMBF exhibited a high conductivity value of approximately 2.83 × 10 S cm, which was favored by the rich amorphous phase as confirmed with X-ray diffraction analysis. The lithium ion transport number and electrochemical stability of the 40 % EMIMBF gel polymer electrolyte were 0.43 and 3.7 V, respectively. These values are acceptable and quite enough for practical device applications. Consequently, the 40 wt% EMIMBF incorporated gel polymer electrolyte could be used to fabricate lithium ion batteries with a suitable selection of other components of the battery system. [ABSTRACT FROM AUTHOR]

Published
2016
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49. Mechanical properties of Ni0.83Co0.15Cu0.02Fe1.9O4−δ+PbZr0.52Ti0.48O3particulate composites by composite oscillator technique and the correlation with the results of magnetoelectric properties

Author

Ramana, M., Reddy, M., Reddy, N., Murty, B., Siva Kumar, K., and Song, Shenhua

Abstract

The xNi0.83Co0.15Cu0.02Fe1.9O4−δ(NCCF) + (1−x)PbZr0.52Ti0.48O3(PZT) particulate magneto ferroelectric composites with x= 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 mole fraction were prepared by conventional ceramic double sintering method. The presence of two phases (perovskite structure of ferroelectric phase and spinal structure of ferromagnetic phase) was confirmed by X-ray diffraction. The magnetoelectric (ME) property of the particulate composites was determined at room temperature as a function of intensity of magnetic field. The temperature variation of the longitudinal modulus (L) and the internal friction (Q−1) of these particulate composites at 104.3 kHz was studied in the wide temperature range 30–420 °C. The temperature variation of the longitudinal modulus in each composition of these particulate composites showed two abrupt minima. One minimum coincided with the ferroelectric — paraelectric Curie transition temperature (θE) and the other with the ferromagnetic-paramagnetic Curie transition temperature (θM). The internal friction measurement also showed two sharp peaks in each composition corresponding to those temperatures where the minima were noticed in the temperature variation of the longitudinal modulus behaviour.

Published
2012
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50. Controlled synthesis of Eu2+-doped barium silicate nanostructures and their optical properties

Author

Lu, Zhengwu, Weng, Luqian, Song, Shenhua, Zhang, Peixin, Luo, Xiongbiao, and Ren, Xiangzhong

Subjects
*EUROPIUM isotopes, *BARIUM silicate, *OPTICAL properties of metals, *METAL microstructure, *PHOSPHORS, *POROUS materials
Abstract

Abstract: Several shapes of Eu2+-doped barium silicate nanostructures have been simply obtained by a hydrothermal method. Hedgehog-like, spherical-shaped, porous irregular spherical, hollow worm-like, and cracked worm shell-like structures are synthesized with changing the molar ratios of Ba/Si in solution. The possible formation mechanisms of these barium silicate nanostructures are proposed. Under an excitation wavelength of 360nm, all the products show broad emission bands from about 400 to 625nm. The UV region excitation band from 300 to 400nm confirms the possibility that the nanostructures could be used as phosphors for white LEDs. [Copyright &y& Elsevier]

Published
2012
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