高压物理学报

Pressure Induced bcchcp Phase Transition of Fe-Co-Ni Alloy at Room Temperature

YANG Hai-Bin, ZOU Guang-Tian, LI Ming-Hui, BAI Yi-Zhen

1991, 5(2): 81-89 . doi: 10.11858/gywlxb.1991.02.001

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Abstract:
The pressure induced bcchcp phase transition and the equation of state for Fe68Co24Ni8 (wt%) alloy have been determined by X-ray powder diffraction in a diamond anvil cell (DAC) at room temperature and high pressure up to 40.5 GPa using Zr-filtered Mo K radiation. The experimental results show that the alloy has bcc structure at normal pressure, the lattice parameter, molar volume and density are (0.287 00.000 1) nm, (7.1190.007) cm3/mol and (7.9810.008) g/cm3, respectively. The bcchcp transition was observed at 20.9 GPa, the pressure region of coexisting phases is about 10 GPa. Within this region, d(002)hcp=d(110)bcc and (002)hcp//(110)bcc are obtained, and the molar volume of the hcp is (0.330.02) cm3/mol smaller than that of the bcc. The c/a ratio for the hcp is 1.6080.004 between 20.9 and 40.5 GPa. As a results of the phase transitions, the interatomic distances in the (002)hcp layer and between (002)hcp layer increase by 1.6% and 0.5%, respectively, due to the increase in coordination number. The Murnaghan equation of state was employed to fit the experimental data with the least square method, B0=(13013) GPa, B0'=12.60.5 for the bcc, and V0=(6.620.04) cm3/mol, B0=(24321) GPa, B0'=6.80.3 for the hcp. The mechanism of crystal structure transition from bcc phase to hcp phase for Fe68Co24Ni8 alloy was discussed in detail.

A Model for Numerical Calculations of Spallation in Brittle Solids

WANG Ze-Ping, HUANG Feng-Lei, YUN Shou-Rong

1991, 5(2): 90-97 . doi: 10.11858/gywlxb.1991.02.002

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Abstract:
By means of Perzyna's brittle dynamic fracture constitutive model and Seaman's experimental results, a new model of brittle fracture is put forward. Numerical calculations of uranium spall processes during impact are carried with the new model. The computations are in fair agreement with the experimental results.

A New Equation of State for Detonation Products

WU Xiong

1991, 5(2): 98-103 . doi: 10.11858/gywlxb.1991.02.003

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Abstract:
Based on the virial theorem and the similarity assumption a new equation of state for detonation products, VLW EOS, has been proposed. The VLW EOS applies not only to the computation of detonation properties of explosives at high pressures but also to the combustion performance parameters of both rocket propellants and gun propellants at higher or moderate pressure conditions.

Microstructures of Superconducting BiPbSrCaCuO Ceramics Treated by High Pressure

WU Bing-Qing, JIN Chang-Qing, WANG Wen-Kui, YAO Yu-Shu

1991, 5(2): 104-111 . doi: 10.11858/gywlxb.1991.02.004

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Abstract:
Microstructures of BiPbSrCaCuO superconductors prepared under various conditions were investigated by means of the scanning electronic microscope (SEM). Focus was placed on the microstructure change of the samples treated by cold pressure and hot pressing. Due to the effects of pressure, average grain sizes in the pressed samples decreased remarkably, and the bulk densities increased greatly to reach 90%~95% of the theoretic density. The high pressure treated samples, on the other hand, are found to be obvious oriented, which may result from the plastic flow under high pressure and the anisotropic growing of the superconducting grains.

High Density Bi-System Superconductor Prepared under High Pressure

YAO Yu-Shu, HUANG Xin-Ming, WU Bing-Qing, JIN Chang-Qing, WANG Wen-Kui

1991, 5(2): 112-117 . doi: 10.11858/gywlxb.1991.02.005

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Abstract:
Superconducting ceramic Bi0.8Pb0.2SrCaCu2Ox was directly obtained for the first time by means of high pressure sintering without any additional annealing. The superconductor sintered at 1 GPa and 500 ℃ for 2 h had a phase transition at 97 K (zero resistance), which was not observed before. The sintered sample reaches a density of 6.23 g/cm3 (about 95% of the theoretical density), much higher than that of the conventionally prepared samples, which usually have densities of only about 4~5 g/cm3.

Effects of Oxidation Characteristics of hBN on the Synthesis of cBN

ZHANG Tie-Chen, MA Wen-Jun, XU Xiao-Wei, ZOU Guang-Tian, GUO Wei-Li, GUO Xue-Bin

1991, 5(2): 118-123 . doi: 10.11858/gywlxb.1991.02.006

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Abstract:
Properties of hBN starting materials have important effect on the synthesis of cBN. In this paper, three types of hBN with different purities were analyzed by Raman, infrared and X-ray diffraction spectra. Effects of the oxidation characteristics of hBN samples as well as the oxides formed under high temperature on the synthesis of cBN were examined. The results show that, besides crystalline degree and impurity, oxidation characteristics have direct effect on the nucleation and growth of cBN.

The Computer Simulation of Fractal Dimension-Ality with Perimeter-Area Relation

WANG Xiao-Wei, DONG Lian-Ke, LONG Qi-Wei

1991, 5(2): 124-129 . doi: 10.11858/gywlxb.1991.02.007

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Abstract:
The paper makes use of perimeter-area relation to simulate the low of variation of fractal dimensionality D under different conditions at the islands closed by Koch curve with initial shapes of equilateral triangles. The conditions necessarily to be met in measurement and the influence of limited level are indicated with application of perimeter-area relation. The physical meaning of these conditions is discussed on realistic application.

The Elastic Properties of Some High Tc Superconductors

WANG Ji-Fang, Manghnani M H, GU Hui-Cheng, LI Feng-Ying

1991, 5(2): 130-136 . doi: 10.11858/gywlxb.1991.02.008

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Abstract:
By using ultrasonic phase comparison method, the longitudinal and shear wave velocities of high Tc superconductors of La2CuO4, La1.85Sr0.15CuO4 and YBa2Cu3O7 have determined. The high pressure results on La1.85Sr0.15CuO4 are also obtained. Based on experimental results, some important elastic characters are derived and superconducting properties are also discussed.

The Spallation of Metal Plates under Short Pulsed Loading

ZHANG Zhong-Zhen, SUN Cheng-Wei, FENG Shu-Ping, GAO Shun-Shou

1991, 5(2): 137-144 . doi: 10.11858/gywlxb.1991.02.009

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Abstract:
Aluminum, brass and steel plates with thickness of 2.0~7.8 mm were impacted by thin mylar flyers at velocities 0.714~2.24 km/s, driven by an electric gun. The pressure pulse duration was about 40~80 ns. It is found from metallographic observations of the target samples that the fracture and spallation mechanism is just the same as that under longer pressure pulse loading. 1 D and 2 D numerical simulations were performed and three spallation criteria, maximum tensile strength, stress gradient and cumulative damage, were employed in elastic-plastic-hydrodynamic codes SSS and WSU. Comparison of calculated and experimental data shows that above criteria are basically appropriate even for such short loading pulse.

Thermal Expansion Coefficients of Solids

YAN Zu-Tong

1991, 5(2): 145-148 . doi: 10.11858/gywlxb.1991.02.010

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Abstract:
Starting from the second law of Grneisen and making use of universal potential energy function as interaction potential function between atoms, we calculated thermal expansion coefficients of the cubic crystal metallic elements and alkali halide crystals at room temperature. The calculated value is in a very suitable agreement with the experimental value.

Problem about Error in Impedance-Match Experiment

MA Min-Xun, GU Yuan

1991, 5(2): 149-153 . doi: 10.11858/gywlxb.1991.02.011

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Abstract:
In this paper, errors in impedance-match experiments are discussed analytically. Numerical evaluations are carried out taking Al-Cu impedance-match as an example. According to our analysis, a few proposals in the design of impedance-match experiments are presented.

Numerical Simulation of Hot Shock Wave in Porous Aluminum

SUN Chong-Feng, ZHANG Ruo-Qi

1991, 5(2): 154-159 . doi: 10.11858/gywlxb.1991.02.012

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Abstract:
In this paper, hot shock wave produced by X-ray radiation in porous aluminum was studied by numerical simulation method. GRAY's three-phase equation of state was used to describe the material states. By improving the widely used p-a relation, we get a better form to describe porous material states. Further more, we revised the spherical shell model of porous material and used it in hot radiation problem to describe the constitution relation of p and a. On the whole, we established a new set of equations to handle the problem we interested in and get some useful results.

1991 Vol. 5, No. 2

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