王瑜
,
林栋梁
,
刘俊亮
,
C.C.Law
金属学报
采用拉伸试验，研究厂不同应变速率（10－5-10－1S-1）下温度对台体积分数为0．8％的TiB2、具有近全片层组织的Ti—47Al—2Mn－2Nb金属间化合物的屈服强度和延伸率的影响，得到合金韧脆转变温度随应变速率升高而升高的变化关系，确定这种含TiB2的TiAL合金的韧脆转变激活能为256kJ／mol这一数值低于无TiB2的合金的韧脆转变激活能（324kJ／mol），接近TiAl合金中原子自扩散激活能结合断口分析和理论计算结果，表明这种含TiB2的TiAl合金韧脆转变过程可能受位错攀移机制控制.
关键词:
TIAl
,
intermetullics
,
BDT
,
strain rate
刘俊亮
,
林栋梁
,
王瑜
,
C.C.Law
,
曹涵清
金属学报
利用透射电子显微镜研究了具有近全片层组织的Ｔｉ－４７Ａｌ－２Ｍｎ－２Ｎｂ合金在液氮（７７Ｋ）温度下变形的微观结构. 结果表明：在层片内部只存在（１／２）〈１１０］普通位错, 但是在γ晶粒内部除了存在（１／２）〈１１０］普通位错外, 也存在〈１０１］和（１／２）〈１１２］超位错. 另外, 在γ晶粒内发现了位错被钉扎后形成的层错偶.
关键词:
TiAl合金
,
null
,
null
Physical Review B
We report the electronic transport properties of a composite system comprising zero dimensional superconducting NbC(C) nanocapsules and carbon nanofiber matrix. DC susceptibility measurements of the nanocomposite indicate that the critical temperature (T-C) of NbC nanocrystals is 10.7 K. The temperature dependence of electrical resistivity of the specimen pellet follows the Mott's T-1/4 law in a temperature range between T-C of NbC and 300 K, owing to a strong degree of structural disorder in the carbon matrix. Below the T-C of NbC, when the change of its electrostatic energy Delta E is far greater than the thermal energy, an electron will be localized on an isolated NbC nanocrystal at very low temperatures, leading to "Coulomb Blockade." As a result, a collective behavior of the single-electron tunneling effect takes place in a three-dimensional granular superconductors' network composed of the NbC/carbon/NbC tunneling junctions. The superconducting gap of NbC crystals is not found in the current-voltage curves, due to the suppression of surface superconductivity through the contact between NbC and carbon shells.
关键词:
zero-dimensional superconductor;granular metal-films;particles;conduction;nanocapsules;percolation;samples
Journal of Materials Research
The oxidation behavior of Zr(2)[Al(Si)](4)C(5) and Zr(3)[Al(Si)](4)C(6) in air has been investigated. The oxidation kinetics of bulk Zr(2)[Al(Si)](4)C(5) and Zr(3)[Al(Si)](4)C(6) at 900-1300 degrees C generally follow a parabolic law at a very short initial stage and then a linear law for a long period with the activation energy of 237.9 and 226.8 kJ/mol, respectively. The oxide scales have a duplex structure, consisting of mainly an outer porous layer of ZrO(2), Al(2)O(3), and aluminosilicate/mullite, and a thin inner compact layer of these oxides plus remaining carbon. The oxidation resistance of Zr(2)[Al(Si)](4)C(5) and Zr(3)[Al(Si)](4)C(6) has been improved compared with Zr(2)Al(3)C(4), and is much better than Zr(3)[Al(Si)](4)C(6) to larger fraction of protective oxidation products, Al(2)O(3) and aluminosilicate/mullite.
关键词:
single-crystals;thermoelectric properties;zrc/zro2 interface;zirconium carbide;high-temperatures;bulk zr2al3c4;carbon;mullite;microstructure;ceramics
Author S.R. Zhou
,
S.R. Qiao
,
S.H. Bai and C.S. Tian Faculty 401
,
Northwestern Polytechnical University
,
Xian 710072
,
ChinaManuscript received 18 October 1998
金属学报(英文版)
The tensile properties of three different carbonfiberreinforced carbon composites (C/C), mat C/C, 2D laminate and 4D C/C, were investigated under the combined influence of temperature and loading rate. From the experiments the following could be concluded: loading rate between 10-1-10 mm/min was valid; the fracture stress of the three kinds of C/C composites increased with increasing temperature in the range from room temperature to 1900, and the initial modulus of 2D laminate C/C composites increased with the increase of temperature up to 2000.
关键词:
tensile testing
,
null
,
null
,
null
Journal of Materials Research
The isothermal oxidation behavior of Zr(2)Al(3)C(4) in the temperature range of 500 to 1000 inverted perpendicular C for 20 h in air has been investigated. The oxidation kinetics follow a parabolic law at 600 to 800 degrees C and a linear law at higher temperatures. The activation energy is determined to be 167.4 and 201.2 kJ/mol at parabolic and linear stages, respectively. The oxide scales have a monolayer structure, which is a mixture of ZrO(2) and Al(2)O(3). As indicated by x-ray diffraction and Raman spectra, the scales formed at 500 to 700 degrees C are amorphous, and at higher temperatures are alpha-Al(2)O(3), and t-ZrO(2) nanocrystallites. The nonselective oxidation of Zr(2)Al(3)C(4) can be attributed to the strong coupling between Al(3)C(2) units and ZrC blocks in its structure, and the close oxygen affinity of Zr and Al.
关键词:
high-temperature oxidation;zirconium carbide;behavior;kinetics;ti2alc;zr
