Wei CHEN (Lab. of Semiconductor Mater. Sci.
,
Institute of Semiconductor
,
Chinese Academy of Sciences
,
Beijing
,
100083
,
China)(To whom correspondence should be addressed)Mianzeng SU(Dept. of Chemistry
,
Peking University
,
Beijing
,
100871
,
China)
材料科学技术（英）
The photoluminescence (PL) and photostimulated luminescence (PSL) of BaFBr:Eu phosphors are reported. In the photoluminescence of BaFBr:Eu, the emission of Eu2+ , e-h recombination and Eu3+ have been observed, while in the photostimulated luminescence only the emission of Eu2+ was observed. This phenomenon may be explained well by the suggestion of a two-band model for the host emission in which the host emission energy may transfer to Eu2+. The difference of excitation in those two processes results in different transfer rates which makes the PL and PSL emission different.
关键词:
Jingguo WANG
,
Guoliang CHEN
,
and Zuqing SUN (State Key Lab. for Advanced Metal Materials
,
University of Science and Technology Beijing
,
Beijing
,
100083
,
China)Hengqiang YE (Lab. of Atomic Imaging of Solids
,
Institute of Metal Research
,
Academia Sinica
,
Sh
材料科学技术（英）
The microstructures and phases of ternary TiAl+Nb alloys containing 50-60 at.-%Al, 0-21 at.-%Nb have been studied using transmission electron microscopy (TEM) and X-ray powder diffraction. The phases present in the alloys and their distribution were found to be a sensitive function of composition. The phase relations between γ-TiAl and γ1 (a new ordered ternary intermetallic compound based on γ-TiAl) were determined. Essentially single γ phase was determined for alloys with relativety low Nb content (≤10 at.-%Nb). the γ1 phase was determined to exist in the composition range containing higher Nb contents (15-21 at.-%Nb). Between γ and γ1 phases, with intermediate Nb contents there is a transitional phase γ1 (a superstructure of γ-TiAl). As for the influence of Al concentration on the phase relations. the γ1 phase was inclined to form in the alloys with relatively high Al contents. The ordering transformation of γ, to γ1 is a continuous ordering process and the transition may be second order.
关键词:
Yueguang YU
,
Jie FU and Xishan XIE(University of Science and Technology Bejing
,
Beijing
,
100083
,
China)Jialong XU and Chunyong JING(Shanghai Iron and Steel Research Institute
,
Shanghai
,
200940
,
China)
材料科学技术（英）
The segregation behaviour and miclostructure of an alloy 718 VADER ingot in comparison with a VAR ingot were studied. The results show that one serious problem of the alloy 718 VADER ingot is dealing with radial chemistry gradients (especially macro-segregation in Nb). The main factor of Nb gradient forming is the flow of Nb rich fluid through passages among the cellular structures driven by centrifugal force from the rotating mold, Detailed structure and micro-segregation studies on ingots impress us that the VADER process does not show the advantage on the improvement of micro-segregation especially in Nb. The cellular structure produced by the VADER process is no more effective in reducjng Nb micro-segregation during homogenization treatment than the dendritic structure by the VAR process. Experimental results lead us to believe that the VADER process is unsuitable to manufacture alloy 718.
关键词:
Qin LIN+
,
Aisheng LIU
,
Wen YE
,
Zongsen YU
,
Dept. of Physical Chemistry
,
University of Science and Technology Beijing
,
Beijing
,
100083
,
China
材料科学技术（英）
In steels 16Mn and X60 with low S content (0. 003～0. 005%), rare earth metals (REM) still show ef- fects on purifying the molten steel and controlling the sulphide morphology. The optimum ratio of RE/S is about 2. 0, which causes lower content of oxygen and inclusions and higher impact toughness. The amount of REM in solid solution in the steel was determined by means of inductive coupling plasma (ICP) spectroscopy. The dissolved REM in low S steel could decrease the propor- tion of pearlite and increase the strength of the steel.
关键词:
rare earths
,
null
,
null
Xianran XING
,
Zhiyu QIAO
,
Wenxia YUAN and Shoukun WEI (University of Science and Technology Beijing
,
Beijing
,
100083
,
China)(To whom correspondence should be addressed)Xiaolong CHEN
,
Guanghui RAO and Jingkui LIANG (Institute of Physics
,
Chinese Academy o
材料科学技术（英）
By X-ray powder diffraction technique and oxygen content analysis, a solid solution Sm1+xBa2-xCu3Oy has been determined in the range 0≤x≤0.4. When x<0.25. the Sm1+xBa2-xCu3Oy presents orthorhombic symmetry, and the orthorhombic-tetragonaJ transition ocCurs at x = 0.25. With the increase of x, TC decreases and finally breaks. The correlation between ox ygen content and phase structure at different quench temperatures related to Sm Ba2Cu3Oy has been investigated as well
关键词:
Kewei GAO
,
Qizhi CHEN
,
Wuyang CHU and Chimei Hsiao(Dept.of Materials Physics
,
University of Science and Technolgy Beijing
,
Beijing
,
100083
,
China)
材料科学技术（英）
Nucleating and propagating of nancrack formed in dislocation free zone (DFZ) for the brittle TiAl alloy has been studied through in-situ tensile test in TEM and analyzed using microfracture mechanics. The resufts show that a lot of dislocations can be emitted from a crack tip when the applied stress intensity Kla i5 larger than the stress intensity for dislocatin emission Kle=1.4 M Pa·m1/2 and a dislocation free zone, which smetimes is a close zone, can form after reaching equilibrium. The DFZ is a elastic zone with large strain and then the stress in the DFZmight equal to the cohesive strength σth because the crack tip is still sharp. When Kla is larger than the stress intensity for nanocrack nucleation Kli =2.4 M Pa·m1/2, the stress within a certain range in the DFZ would equal to σth and then a nanocrack initiates in the DFZ or sometimes at the notch tip. The nanocrack formed in the DFZ is stable and can propagate a small distance in cleavage mode through multiplication and movement of dislocation in the plastic zone, during keeping constant displacement. Increasing Kla can make the crack stably propagate continuously or discontinuously and it means that the stre5s intensity for crack propagation, Klp, is larger than Kli. Therefre, Kle
关键词:
Wei CHEM and Ruzhang MA(Dept. of Materials Physics
,
University of Science and Technology Bejing
,
Bejing
,
100083
,
China)
材料科学技术（英）
The relations of oxygen content, critical temperature TC and mean ionization potential < U0> of superconducting oxides are reported. We found that in oxides oxygen is the major element which governs their < U0> te values and thus oxygen content plays an jmportant role in their superconducting properties. As for Y(123)- and T1-systems oxygenation may improve their TC values, but for Biand Hg-systems oxygenation process is not so important. In Y(123), as the oxygen content increase results in the increase of TC upon < U0>to, while the substitution of Ba2+ by Sr2+ causes the decrease of TC upon < U0 >. These results may provide some clues about the superconductivity of oxides and support further that < Uo > is really a good criterion for oxide superconductivity. Two kinds of possible superconducting oxides are predicted in this paper according to the mean ionization potential criterion.
关键词:
