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991.
Effect of different alloyed layers on the high temperature oxidation behavior of newly developed Ti2AlNb-based alloys 总被引:1,自引:0,他引:1
Hongyan Wu Pingze ZhangHaofeng Zhao Ling WangAigen Xie 《Applied Surface Science》2011,257(6):1835-1839
The application of titanium aluminide orthorhombic alloys (O-phase alloys) as potential materials in aircraft and jet engines was limited by their poor oxidation resistance at high temperature. The Ti2AlNb-based alloys were chromised (Cr), chromium-tungstened (Cr-W) and nickel-chromised (Ni-Cr) by the double glow plasma surface alloying process to improve their high temperature oxidation resistance. The discontinuous oxidative behavior of Cr, Cr-W and Ni-Cr alloyed layers on Ti2AlNb-based alloy at 1093 K was explored in this study. After exposing at 1093 K, the TiO2 layer was formed on the bare alloy and accompanied by the occurrence of crack, which promoted oxidation rate. The oxidation behavior of Ti2AlNb-based alloys was improved by surface alloying due to the formation of protective Al2O3 scale or continuous and dense NiCr2O4 film. The Ni-Cr alloyed layer presented the best high-temperature oxidation resistance among three alloyed layers. 相似文献
992.
993.
J. Arghavani F. Auricchio R. Naghdabadi A. Reali S. Sohrabpour 《International Journal of Plasticity》2010
This paper presents a new phenomenological constitutive model for shape memory alloys, developed within the framework of irreversible thermodynamics and based on a scalar and a tensorial internal variable. In particular, the model uses a measure of the amount of stress-induced martensite as scalar internal variable and the preferred direction of variants as independent tensorial internal variable. Using this approach, it is possible to account for variant reorientation and for the effects of multiaxial non-proportional loadings in a more accurate form than previously done. In particular, we propose a model that has the property of completely decoupling the pure reorientation mechanism from the pure transformation mechanism. Numerical tests show the ability to reproduce main features of shape memory alloys in proportional loadings and also to improve prediction capabilities under non-proportional loadings, as proven by the comparison with several experimental results available in the literature. 相似文献
994.
The electronic structures of most semiconductor alloys are smooth functions of their composition. Binary alloys of group IV semiconductors are usually easy to prepare at any concentration, but this is not the case for the Ge1-xSnx alloy. Homogeneous alloys as required for nano- and optoelectronics device applications have proved difficult to form for x above a temperature-dependent critical concentration, above which Sn exhibits the tendency to segregate in the metallic cubic β phase, spoiling the semiconducting properties. The underlying mechanism for this segregation and critical concentration was not known.Through previous accurate ab initio local defect calculations we estimated the scale of energies involved in the immediate environment around a large number of Sn defects in Ge, the relaxed configurations of the defects, and the pressure directly related to the elastic field caused by the defects. This detailed information allowed us to build a simple statistical model including the defects most relevant at low x, namely substitutional α-Sn and non-substitutional β-Sn (in which a single atom occupies the centre of a Ge divacancy). Our model enables us to determine at which concentration β defects, which exhibit a tendency to segregate, can be formed in thermal equilibrium. These results coincide remarkably well with experimental findings, concerning the critical concentration above which the homogeneous alloys cannot be formed at room temperature. Our model also predicts the observed fact that at lower temperature the critical concentration increases. 相似文献
995.
996.
997.
Aditya M. Vora 《Journal of Non》2011,357(10):2039-2045
The theoretical investigations of the superconducting state parameters (SSP) viz. electron-phonon coupling strength λ, Coulomb pseudopotential μ?, transition temperature TC, isotope effect exponent α and effective interaction strength NOV of (Ni33Zr67)1 − xMx (x = 0, 0.05, 0.1, and 0.15, M = Cu) ternary amorphous superconductors have been reported using Ashcroft's empty core (EMC) model potential. Five local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru-Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) are used in the present investigation to study the screening influence on the aforesaid properties. The TC obtained from Sarkar et al. (S) local field correction function is found in excellent agreement with available theoretical data. Quadratic TC equation has been proposed, which provides successfully the TC values of ternary amorphous alloys under consideration. Also, the present results are found in qualitative agreement with other such earlier reported data, which confirm the superconducting phase in the superconductors. 相似文献
998.
A thermodynamic assessment of the ternary Cu‐Mg‐Si system was made in its copper‐rich region in relation with the development of a thermodynamic database for Cu‐Mg alloys. The adjustable parameters of the binary end‐systems (Cu‐Mg, Cu‐Si and Mg‐Si) were taken from the literature and those of the Cu‐Mg‐Si system were optimized using experimental thermodynamic and topological data. For the sake of simplicity, the solution phases were described with the substitutional solution model and the intermetallic compounds were treated as plain semi‐stoichiometric phases ((A,B)pCq‐type). The assessment developed is applicable for magnesium contents up to 20 wt% (i.e. magnesium mole fractions ≈0.4) and silicon contents up to 16 wt% (i.e. silicon mole fractions ≈0.3). (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
999.
《Physics and Chemistry of Liquids》2012,50(4):562-570
Shear viscosity measurements were performed for liquid Co–Sn alloys over a wide temperature range above the respective liquidus temperatures. A high temperature oscillating-cup viscometer was used. It was found experimentally that viscosity as a function of temperature obeys an Arrhenius law. The data were compared with calculated values, obtained from different thermodynamic approaches. A good agreement was found between experimental results and calculated ones by the Budai–Benkö–Kaptay model. 相似文献
1000.
《Physics and Chemistry of Liquids》2012,50(3):245-259
Thermodynamic and surface properties of Ge–Ga and Ge–Sb liquid alloys have been studied using statistical mechanical formulations based on complex formation and that based on the concept of layered structure near the interface. The study showed that low level of complex formation of the form Ge 2 Sb exists in Ge–Sb toward the Ge-rich end of the concentration range and the surface properties of Ge–Ga are almost equal to their corresponding bulk equivalent. 相似文献