LI Gang
,
WANG Zhongguang
,
LI Guangyi(State Key Laboratory of Fatigue and Fracture for Materials
,
Institute of Metal Research
,
Chinese Academy of Sciences
,
Shenyang 110015
,
China)V.OVCHARENKO(Institute of Strength Physics and Materials Science
,
Russian Academy of Science
,
Siberian Branch
,
Tomsk
,
Russia) Manuscript received 3 May 1995
金属学报(英文版)
Self propagating high temperature synthesis(SHS) under compression was utilized to obtain an intermetallic compound Ni_3 Al by using elemental powders.The microstructure of the SHS product was observed by optical microscopy(OM) and scanning electron microscopy(SEM).The results reveal that the SHS Ni3Al is a single-phase polycrystalline alloy wilh LI2 crystal structure.Tensile tests were conducted from room temperature to 800℃ both in air and in vacuum.The results show that the SHS Ni_3Al exhibits an anomalous temperature dependence of ultimate tensile strength.The ultimate tensile strength in vacuum is much higher than that in air over the whole temperature range.Fracture surfaces are characterized by the brittle grain boundary fracture and the intergranular fracture mode can not be affected markedly by the test environment.
关键词:
:Ni_3Al
,
null
,
null
,
null
Sergey N.Kulkov Alexander G.Melnikov Institute of Strength Physics and Materials Science
,
The Russian Academy.of Science
,
Siberian Branch
,
Tomsk
,
634055
,
RussiaYanchun ZHOU Shengqi CHEN Zhe QU Institute of Metal Research
,
Academia Sinica
,
Shenyang
,
110015
,
China
材料科学技术（英）
The effects of shock loading on the morphology,grain growth during heating and phase transforma- tion of ZrO_2 have been investigated.It is shown that shock loading may be efficiently used to modify submicron ceramic powders with nanocrystalline structure.After shock loading,the critical diameter of ZrO_2 particles transformed from tetragonal to monoclinic decreased due to stored strain energy. Annealing of powders resulted in reversible transformation to the tetragonal without considerable grain growth up to 1200℃.
关键词:
submicron ceramics
,
null
,
null
,
null
Physics Letters A
Cyclotron resonance of a magnetopolaron in a harmonic quantum dot with the resonant magnetic field normal to the plane of the quantum dot is investigated theoretically. It is shown that for a resonant magnetic field, the two cyclotron masses (m+* and m-* ) in a harmonic quantum dot are each split into two cyclotron masses, respectively. The cyclotron mass (m+*) decreases with decreasing size of the quantum dot, the stronger the magnetic field strength, the larger the cyclotron mass. The lower branch of the cyclotron mass (m-*) increases linearly with increasing magnetic field strength. The upper branch of the cyclotron mass (m-*) is larger than the bare band mass and enhances as the magnetic field strength increases.
关键词:
size dependence;electron;polarons;states;energy;gaas;cdse
Synthetic Metals
Considering the next-nearest neighbor hopping interaction of the electrons, we investigate the magnon excitation of a theoretical model proposed for quasi-one-dimensional pi-conjugated organic ferromagnetic polymer. By employing the random-phase approximation (RPA), the magnon excitation spectrum is obtained. It is found that the lowest branch-the acoustic mode in excitation spectrum displays the characteristic of the ferromagnetic magnon, and with the increase of the next-nearest neighbor hopping interaction, the ferromagnetic correlation in the system will be weakened.
关键词:
magnetic polymer;magnon excitation;random-phase approximation
Communications in Theoretical Physics
A new theory of spectral thermal shifts (TS) and thermal broadenings (TB) has been developed. For the first time, by taking into account all the Gamma M in the electron-phonon interaction (EPI), all the levels and the admixtures of wavefunctions within d(3) electronic configuration, the microscopic expressions; of all the parameters in three terms of TS from EPI have been derived; their values for the R-1, R-2 and ground levels of ruby have been evaluated; the contributions to TS from thermal expansion have also been calculated; the transition probabilities of direct and Raman processes have microscopically been calculated; and then, the unified calculation of the TS of R-1 and R-2 lines and zero-field-splitting (ZFS) for the ground state and the TB of R, R' and B line-groups has been accomplished. The results are in very good agreement with a lot of experimental data. It is found that the contributions from the second-order term of EPI Hamiltonian are dominant in the optical-branch term of ZFS and Raman terms of R-1 line, R-2 line and ZFS; the optical-branch terms play an important role in TS and increase rapidly with temperature, and the optical-branch terms of R1 and R2 lines have opposite signs due to the effects of neighbor levels; the neighbor-level terms for R1 and R-2 lines are very important and it is the admixtures of wavefunctions caused by Coulomb and/or trigonal-field and/or spin-orbit interactions that make them nonzero; the contributions to TS from thermal expansion are also important (especially for ZFS).
关键词:
crystal fields;optical properties;phonons;electronic structure;thermal expansion;r-line;temperature
Advanced Functional Materials
We report the growth mechanism, cathodoluminescence and field emission of dual phase ZnS tetrapod tree-like heterostructures. This novel heterostructures consist of two phases: zinc blende for the trunk and hexagonal wurtzite for the branch. Direct evidence is presented for the polarity induced growth of tetrapod ZnS trees through high-resolution electron microscopy study, demonstrating that Zn-terminated ZnS (111)/(0001) polar surface is chemically active and S-terminated ((1) over bar(1) over bar(1) over bar)/(000 (1) over bar) polar surface is inert in the growth of tetrapod ZnS trees. Two strong UV emissions centered at 3.68 and 3.83 eV have been observed at room temperature, which are attributed to the bandgap emissions from the zinc blende trunk and hexagonal wurtzite branch, indicating that such structures can be used as unique electromechanical and optoelectronic components in potential light sources, laser and light emitting display devices. In addition, the low turn-on field (2.66 V mu m(-1)), high field-enhancement factor (over 2600), large current density (over 30 mAcm(-2) at a macroscopic field of 4.33 V mu m(-1)) and small fluctuation (similar to 1%) further indicate the availability of ZnS tetrapod tree-like heterostructures for field emission panel display. This excellent field-emission property is attributed to the specific crystallographic feature with high crystallinity and cone-shape patterned branch with nanometer-sized tips. Such a structure may optimize the FE properties and make a promising field emitter.
关键词:
single-crystal nanorings;nanowires;nanobelts;nanostructures;photoluminescence;nanocrystals;fabrication;nanorods;arrays;cdte
Communications in Theoretical Physics
By taking into account all the irreducible representations and their components in the electron-phonon interaction (EPI) as well as all the levels and the admixtures of wavefunctions within d(3) electronic configuration, the thermal shifts (TS) of the ground-state zero-field-splitting (GSZFS) due to EPI for ruby have microscopic-theoretically been calculated; the contribution to TS of GSZFS from thermal expansion has also been calculated. The results are in very good agreement with experiments. It is found that the contributions from the first-order perturbation of the second-order term in EPI Hamiltonian are dominant in the Raman term and optical-branch term for TS of GSZFS; the different between the TS due to EPI of t(2)(3 4)A(2) +/-1/2e(2) (G(2)) level and the TS due to EPI of t(2)(3) (4)A(2) +/- 3/2e(2) (G(1)) level gives rise to the TS due to EPI of GSZFS, which is very small in comparison with the TS due to EPI of G(2) or G(1) level. Among various terms in TS of GSZFS, Raman term is the largest one and the signs of the Raman term and optical-branch term are opposite to the sign of the thermal-expansion term; the optical-branch term plays an important role in TS of GSZFS and increases rapidly with temperature; all various contributions to TS of GSZFS have to be taken into account, since the subtle balance among them determines the total result. The comparison between the features of TS of GSZFS and those of TS of R-1 and R-2 lines has been made. For TS of GSZFS, the contribution from thermal expansion is especially important; the neighbor-level term is insignificant.
关键词:
optical materials;crystal fields;electronic paramagnetic resonance;phonons;thermal expansion;pressure-induced shifts;optical-spectra;mgo-v2+
H.F. Wang
,
J.J. Guo
,
G.F. Mi
,
null
,
null
,
null
,
null
,
null
,
null
,
null
,
null
金属学报(英文版)
Solute diffusion controlled solidification model was applied to simulate the columnar to equiaxed transition (CET) during directional solidification of of TiAl alloys. The simulation results showed that the solutal interactions from growing equiaxed grains play an important role on CET, which can render a large fraction of seeds inactive. The effects of the applied temperature gradient and pulling speed, the equiaxed seed spacing and nucleation undercooling on the CET are investigated in present simulation. It indicated that the columnar branch spacing depends not only on the temperature gradient and the pulling speed, but also number of the seeds, a spacing adjustment can occur through initiation of seeds that develop into new columnar grains. The dependence of the CET on the temperature gradient and pulling speed, qualitatively agrees with the analytical CET model of Hunt.
关键词:
TiAl alloys
,
null
,
null
LONG Hongming
,
FAN Xiaohui
,
JIANG Tao
,
DAI Linqing
钢铁研究学报(英文版)
An expert system skeleton tool of sintering process was constructed using objectoriented method, which can actualize two functions, ie, the shell function and the program function. The skeleton tool offered a platform to build a prototype system, to program class code, and to develop the expert system. Four branch expert systems were developed using the skeleton tool including the control of chemical composition, the control of sintering process state, the control of expended energy, and the diagnosis of abnormity. It is found that the performance of all systems is satisfactory in practice.
关键词:
sintering process;expert system;skeleton tool;knowledge base;illation engine
LIU Yongkun Southwestern Institute of Technology and Engineering
,
Chongqing
,
ChinaYANG Shihao Shandong Polytechnical University
,
Jinan
,
China
金属学报(英文版)
Using liquid quenching technique,the change of growth mode of graphite in cast iron melt was analysed.Based on the interface structure theory of crystal growth,the concept of multiplication of spiral growth steps was advanced and two basic multiplication models were given.It was proposed that multiplication of spiral steps is responsible for the change of growth mode of graphite in cast iron melt.The modifying elements such as Ce promote multiplication of spiral steps,which is regarded as the core of modification.Origination of screw dislocation and branch of the sector blocks in radius direction,both of which are essential to spheroidization of graphite in the melt,are caused by multiplication of spiral steps:and so is thickening of graphite plates.
关键词:
graphite
,
null
,
null
,
null
,
null
