Junhua LIU+
,
Dept. of Manufacturing Engineering
,
Beijing University of Aeronautics and Astronautics
,
Beijing 100083
,
ChinaZutang WANG
,
Dept. of Mechanical Engineering
,
Tsinghua University
,
Beijing
,
100084
,
China
材料科学技术（英）
The effects of sintering on the microstructure and the critical current density of Ag-sheathed BiPbSrCaCuO (2223) superconducting tapes prepared by the powder-in-tube technique were in- vestigated. The microstructure of oxide layer and the J_C at 77 K were strongly dependent on the sintering condition. The optimum sintering temperature, time and cooling rate to maximize J_C values were in the range about 840-850℃, 100-200 h and 50-100℃/h, respectively.
关键词:
BiPbSrCaCuO
,
null
,
null
,
null
C.G. Zhou
,
H.B. Xu and S.K. Gong (Department of Materials Science and Engineering
,
Beijing University of Aeronautics and Astronautics
,
Beijing 100083
,
China) K. Y. Kim (Department of Materials Science and Engineering
,
Pohang University of Science and Technology
,
San31
,
Hyoja-dong
,
Pohang 790-784 Korea)
金属学报(英文版)
The halide-activated pack cementation method is utilized to deposit aluminide coat- ings on TiAl alloys. Emphasis is placed on the effect of alloying elements on the aluminizing behavior of TiAl alloy. The addition of a small amount of Nb or Cr in the TiAl improves significantly the aluminizing kinetics of TiAl alloys by increasing the solid-state division of Al through the formation of stable TiAl3 layer. The TiAl3 layer formed on the TiAl alloyed with Nb or Cr has better toughness than the TiAl3 formed on the non-alloyed TiAl. The reason for better toughness of the coating formed on TiAl is that partial TiAl3 with tetragonal structure was changed to high symmetry cubic L12 structure since Nb or Cr was dissolved into TiAl3. The TiAl3 layer formed on the TiAl alloyed with Nb or Cr has much better oxidation resistance than the TiAl3 layer formed on the non-alloyed TiAl. It is attributed to change in the crystal structure of TiAl3 from the brittle tetragonal DO22 to the ductile cubic L12 by addition of small amount of Nb or Cr.
关键词:
TiAl
,
null
,
null
,
null
X. L. Wu
,
J.H. Liu and X.Y. Chen Department of Materials Science and Engineering
,
Beijing University of Aeronautics and Astronautics
,
Beijing 100083
,
China
金属学报(英文版)
The morphology and chemical compositions of surface and corrosion phases for two aluminum alloys(7075 and 2024 ) in the aqueous mediums containing sulfate reducing bacteria(SRB) were studied by the methods of scanning electron microscopy (SEM) and energy dispersive x ray analysis (EDXA). The results showed that serious pitting corrosion took place when aluminum alloys were exposed in the mediums containing SRB, whereas no pitting corrosion were found on the surfaces of aluminum alloys only exposed in blank mediums non containing SRB. It was demonstrated with EDXA that corrosion of aluminum alloys exposed in the solutions containing SRB, whereas the corrosion in the solution non containing microorganisms was attributed to the presence of chloride ions(Cl ).
关键词:
aluminum alloys
,
null
,
null
,
null
Zuoguang ZHANG
,
Weihong ZHONG and Huancheng SONG(Dept. of Materials Science and Engineering
,
Beijing University of Aeronautics and Astronautics
,
Beijing 100083
,
China)
材料科学技术（英）
Structures used in aerospace are influenced by temperature. So coefficient of thermal expansion (CTE) is not only an important parameter of materials, but also a significant parameter of structural design of spacecrafts with high dimensional stability. In this paper, based on the analysis of the data from tests, theoretical formulae for predicting CTE and mechanical properties of hybrid composites are presented, and the calculation program is compiled. All the equations are verified by experiments. Optimization is conducted by computer. The results and methods presented in this paper can be used both in optimal design of hybrid composites with zero CTE and in design of hybrid composites with any certain CTE value
关键词:
Shengkai GONG
,
Huibin XU (Dept. of Materials Science and Engineering
,
Beijing University of Aeronautics and Astronautics
,
Beijing 100083
,
China)
材料科学技术（英）
Iron-nitride films were prepared by reactive sputtering, and the effect of annealing treatment on the structures was investigated by means of in-situ electron microscopy and high resolution electron microscopy (HREM). As-deposited films were observed to be a mixed structure of a few ultrafine ε-Fe2-3N particles existing in the amorphous matrix. lt was found that the structurerelaxation in the amorphous occurred at 473 K, and the ultrafine grains began to grow at the higher annealing temperatures. The transition of the amorphous to ε-Fe2-3N was almost completed at 673 K. It is considered that the formation of the ideal ε-Fe3N is originated from the ordering of the nitrogen atoms during the annealing in vacuum. On the other hand, γ'-phase (Fe4N) was seen to precipitation of ε-phase at 723 K. Two possible modes are proposed in the precipitation of γ'-phase, depending on the heating rate and crystallographic orientation relationships. i.e. [121]ε [001]γ, (210)ε(110)γ and [100]ε[110]γ, (001)ε(111)γ. In addition,α-Fe particles were observed to form from the γ'-phase at high temperatures. We assumed that these structural changes are due to the diffusion of nitrogen and iron atoms during the annealing,except for the case of the precipitation of the γ'-phase as depicted above. The results obtained in this work are in a good agreement with the assumption.
关键词:
Y.L. Xu
,
G.H Liu and S. Tian (Department of Materials Science and Engineering
,
Beijing University of Aeronautics and Astronautics
,
Beijing 100083
,
China)
金属学报(英文版)
ZnS-Diatnond cotnPOsites (ZnS/D) were fabricated by hot pressing to obtain a ZnS ithered transparent materials with incmeed toughness. The relations of the mechanical properties and the diomond contents were investigated. It was determined that,when the content of diamond is in the mnge hem 1% to 10%, the toughness of the composite fits the equation KIC = cexp(a+bx). The constants c, a, and b determined experimentally are 10-6, d.47 and 9.70 respectively.
关键词:
ZnS
,
null
,
null
,
null
