WADSWORTH Jeffrey and FLUSS Michael(Chemistry and Materials Science Directorate
,
Lawrence Livermore National Laboratory
,
Livermore
,
CA 94551)
金属学报(英文版)
The role of the National Laboratories is summarized from the era of post World War II to the present time. The U.S. federal government policy for the National Laboratories and its influence on their materials science infrastructure is reviewed with respect to .determining overall research strategies, various initiatives to interact with industry (especially in recent years),building facilities that serve the nation, and developing leading edge research in the materials sciences. Despite reductions in support for research in the U.S. in recent years, and uncertainties regarding the specific policies for Research &Development (R&D) in the U.S., there are strong roles for materials research at the National Laboratories. These roles will be centered on the abilities of the National Laboratories to field multidisciplinary teams, the use of unique cutting edge facilities, a focus on areas of strength within each of the labs,increased teaming and partnerships, and the selection of motivated research areas. It is hoped that such teaming opportunities will include new alliances with China, in a manner similar, perhaps, to those recently achieved between the U.S. and other countries.
关键词:
: U.S. Materials Science. U.S. National Laboratories and Facilities
,
null
Advanced Materials
The key to the formation of nanocrystallites from amorphous solids lies in the annealing temperature. This aspect of the preparation of nanocrystalline materials is covered, as are other attractive features of this method, for example, that it can be applied to most alloy and pure element systems, large quantities of nanocrystalline samples can be produced, and the grain size can be controlled. The properties of these materials are also described and it is concluded that more studies on 3D bulk: porosity-free, and clean samples are needed.
关键词:
ultrafine grain-structure;alloys;selenium;sizes
Nanostructured Materials
Lattice parameters for nanocrystalline (nc) materials were found to be alerted with respect to the corresponding coarse-grained polycrystalline counterparts in several systems. In this work, experimental evidences of the lattice structure distortion in various nc materials processed by means of different approaches will be summarized and discussed. Strong evidences showed the lattice structure distortion in nc samples which is manifested by an evident change in the lattice parameters, Debye-Waller parameter, and the thermal properties of the nanocrystalline lattice. These results imply that the property changes of nc materials should be attributed not only to the numerous non-equilibrium grain boundaries, but to the distorted nanocrystallites as well. (C) 1999 Acta Metallurgica Inc.
关键词:
x-ray-diffraction;thermal-properties;selenium;metals
材料科学技术（英文）
In this work, we demonstrated that the differential scanning calorimetry (DSC) is not always reliable in measuring thermal stability and grain growth process in nanocrystalline materials by a quantitative analysis and comparison of the DSC data measured in nanocrystalline Ni-P and Hf-Ni samples.
关键词:
thermal-stability;ni;alloys
Materials Letters
High resolution electron microscopy studies of nanocrystalline Pd and (Fe-0.99, Mo-0.01)(78)Si9B13 indicate that the atomic structures of the grain boundaries consist of both ordered and disordered regions. The microstructure in ordered regions of the grain boundaries shows curved and little distorted appearance. In some areas, however, nanovoids and imperfect or disordered regions are also observed at the grain boundaries. The defects in the grains, such as five-fold twins, edge and 60 degrees dislocations, are also observed. The nature of these defects is similar to those normally observed in conventional coarse-grained polycrystals.
关键词:
randomly arranged atoms;solid-state structure;nanophase materials;grain-boundaries;palladium
Ke LU National Key Laboratory for RSA
,
Institute of Metal Research
,
Academia Sinica
,
Shenyang
,
110015
,
ChinaManling SUI Department of Materials Science and Engineering
,
Northeastern University
,
Shenyang 110006
,
China
材料科学技术（英文）
A thermodynamic analysis of the ultrafine crystallites in nanocrystalline materials was presented in this work.It was deduced that the structure of the nm-sized crystalline grains is different from the perfect crystal lattice,characterized by two possible structure changes;supersaturation of alloy ele- ments and crystal lattice distortion resulted from supersaturation of vacancies.Some experimental ev- idences in the literature,which are in agreement of the thermodynamic consideration,indicate that the structure changes in the nm-sized crystallite seems to be a consequential feature of the nanocrystalline materials.
关键词:
nanocrystalline materials
,
null
,
null
G.Q. Zhang
金属学报(英文版)
The status of research, development of superalloys and materials processing & fabrication technologies for aero-engine applications in China Aviation Industry, with an emphasis on recent achievements at BIAM including directionally solidified and single crystal superalloys for blade and vane applications, wrought superalloys for aero-engine disks and rings, and powder metallurgy (PM) superalloys for high performance disk applications were described. It was also reviewed the development of new class of high temperature structural materials, such as structural intermetallics, and advanced material processing technologies including rapid solidification, spray forming and so on. The trends of research and development of the above mentioned superalloys and processing technologies are outlined. Cast, wrought and PM superalloys are the workhorse materials for the hot section of current aero-engines. New high temperature materials and advanced processing technologies have been and will be the subject of study. It is speculated that high performance, high purity and low cost superalloys and technologies will play key roles in aero-engines.
关键词:
superalloy
,
null
,
null
Journal of Applied Physics
This article demonstrates, from the theoretical paint off view, chat owing to the phonon-assisted relaxation rate of the excited electron-hole pair's transiting to lower states decreases as the scale of Si particle is reduced, the optically excited electron-hole pair in the nanometer silicon particle with sufficient small scale generally tunnel inter the SiOx layers which enclose the Si particles and recombine radiatively through the luminescence centers there to emit visible Sight rather than recombine radiatively in the Si particles. It is proved also that when the density of the luminescence center is 2.5X10(22)/m(3) the upper limit of the average scale of the nanometer silicon particles in the ensemble capable of emitting red light in room temperature is around 8.7 nm, which is. much bigger than the generally estimated value of 3 nm. (C) 1997 American Institute of Physics.
关键词:
silicon films;light-emission;photoluminescence;mechanism;absorption;layers;nm
