Creep behavior and effect factors of a TiAl–Nb alloy at high temperature

The effect of solution treatment on the microstructure and creep properties of forged TiAl–Nb alloys was investigated. The results showed that the microstructure of forged alloy mainly consisted of γ/α₂ lamellar colonies and fine equiaxed recrystallized γ/α₂ grains. During the solution treatment the microstructure of the alloy transformed into a fully lamellar structure due to the lamellar colonies growth by consuming equiaxed grains. Compared with the forged alloy the creep life of the solution treated alloy at 800 ?°C/220 ?MPa increased from 116 ?h to 339 ?h. The better creep resistance may be attributed to the transform of fine equiaxed γ/α₂ grain to the lamellar colonies with serrated grain boundaries due to the solution treatment. The deformation mechanism of the solution treated alloy during creep is considered to be dislocation slipping within the lamellar γ/α₂ phases, and the dislocation movement may be hindered by the γ/α₂ interface and the formation of dislocation tangles. The interaction of the dislocations with the tangles may increase the resistance of the dislocation motion and hence improve the creep resistance of the alloy. It was found that during the creep of the forged alloys the cracks mainly initiated at the equiaxed grain, and in the solution treated alloy the cracks initiated at the grain boundaries. As creep continued the cracks propagated and connected to each other, leading to the damage and rupture of the forged and solution treated alloys.     

一类二阶具多偏差变元微分方程的周期解

主要讨论了一类二阶具多偏差变元的泛函微分方程周期解的存在性,利用重合度理论和关于周期函数的最佳不等式,得到了文中的若干结论．     

网约车平台两阶段定价研究

平台在不同的发展阶段所面临的效应并不相同，必须采取针对性的定价策略。现有文献对两阶段定价策略和临界情况的研究比较有限。本研究依据网约车平台发展周期，研究了“扩张+盈利”两阶段的模式背后的定价机理。研究表明：扩张阶段只存在交叉网络外部性的情况下，网约车平台对双边用户的最优定价与交叉网络外部性和盈利阶段所面临的组内网络外部性正相关。盈利阶段同时存在交叉网络外部性和组内网络外部性的情况下，最优定价与交叉网络外部性正相关，与组内网络外部性负相关。本研究还探讨了网约车平台快速积累用户实现“烧钱”向“盈利”模式转变的影响因素，并给出相应的管理启示。     

高含CO2油田腐蚀环境下16Mn管线钢电化学腐蚀行为

油田开发生产中，高CO2环境会引起集输管线严重腐蚀。为了给高CO2环境腐蚀防护方案提供技术依据，通过动电位极化扫描和电化学阻抗测试研究了温度、溶解O2对16Mn管线钢在高含CO2腐蚀环境下电化学腐蚀行为的影响。结果表明：随着温度的升高，16Mn钢的腐蚀电位减小，腐蚀倾向性增强，但腐蚀电流密度大大减小，表现出较好的抗温耐蚀性能；同样温度下，16Mn钢在饱和O2环境中相比不含O2时极化曲线的腐蚀电流密度减小，交流阻抗谱的电荷传递电阻大大增加，且低温时更显著，表现出较好的低温抗氧耐蚀性能。