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991.
Oxidation of TiAl based intermetallics 总被引:3,自引:0,他引:3
The high temperature oxidation behaviour of the binary and ternary alloys of the Ti–48Al system was studied at different temperatures.
The primary objectives of this work were the establishment of the activation energies, the migration tendencies of the alloy
species, mechanism of oxidation and chemistry of the oxide scales. The ternary additions were Cr (1.5 at 19%), V (2.2 at%),
W (0.2 at%) and Mn (1.4 at%). The addition of ternary additions did not play a significant role in the oxidation behaviour
at 704°C. At 815°C the alloys with Cr and V exhibited linear oxidation behaviour with large weight gains while the base Ti–48Al
alloys exhibited the best behaviour. At 982°C the Mn-containing alloy was the worst, exhibiting a linear oxidation behaviour
while the alloy with V and W and the base alloy with 400 p.p.m. oxygen exhibited the best oxidation behaviour. At 982°C the
outermost oxide layer in contact with air is always near stoichiometric TiO2. In all the alloys a layer of porosity is created just below the outer TiO2 layer by the Kirkendall mechanism due to the rapid outward diffusion of Ti atoms. The addition of trivalent atoms like Cr
in small amounts appear to be detrimental to the oxidation process as they can generate additional oxygen vacancies while
the addition of atoms with valence of 5, such as V, and 6, such as W, appear to have beneficial effect on the oxidation behaviour
at 982°C by tying up oxygen vacancies.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
992.
993.
994.
Frateschi N.C. Osinski J.S. Beyler C.A. Dapkus P.D. 《Photonics Technology Letters, IEEE》1992,4(3):209-212
Low-threshold current (as low as 3.0 mA) and high-external efficiency (≈88%) InGaAs/GaAs lasers emitting at 1 μm under a stable fundamental transverse mode were obtained by using the temperature engineered growth technique for the growth on prepatterned substrates 相似文献
995.
Ultrathin dielectric materials that provide high capacitance values are needed for 64- and 256-Mb stacked DRAMs. It is shown that capacitance values as high as 12.3 fF/μm2 can be obtained with ultrathin nitride-based layers deposited on rugged polysilicon storage electrodes. These films present the reliability and low leakage current levels required for 3.3-V applications. The nitride thickness, however, cannot be scaled much below 6 nm to avoid the oxidation-punchthrough mechanisms that appear when too-thin films are unable to withstand the reoxidation step 相似文献
996.
997.
Howerton M.M. Moeller R.P. Bulmer C.H. Burns W.K. 《Photonics Technology Letters, IEEE》1992,4(10):1127-1129
Stable operation of an integrated optic modulator is demonstrated using a 1.3 μm doubly polarized laser as a depolarized source in conjunction with a long run of ordinary fiber. The laser is found to be unusually susceptible to feedback due to gain competition between the polarization modes. The resulting low-frequency polarization noise is significantly reduced by the addition of fiber isolators to the system 相似文献
998.
999.
The unloaded Q -factor of a dielectric resonator is degraded due to conductor loss when it is placed in an MIC environment. The authors report approximate but quite accurate closed form expressions for the Q -factor due to conductor loss. The results obtained are in good agreement with those of rigorous numerical methods. The effect of geometrical parameters on the useful tuning range of the structure is studied. Finally, an explicit relationship between the resonant frequency sensitivity factors and the conductor Q -factor is derived 相似文献
1000.
Pursuing optimal solutions for large scale transmission network planning problems is a formidable task due to their combinatorial nature and also due to the nonconvexities involved. Successful approaches using hierarchical Benders decomposition incur in a high computational cost mainly due to the need to solve a large integer program (the investment sub-problem) for every Benders iteration. In this work the authors propose to use heuristics within the decomposition framework, therefore avoiding to solve to optimality each integer sub-problem. The global computational effort is substantially reduced, and allows coping with large problems that would be intractable using classical combinatorial techniques. Case studies with the 6 bus Garver test system and a reduced Southeastern Brazilian power network are presented and discussed 相似文献