钛合金保载疲劳的成分及温度依赖性的第一原理研究

保载疲劳显著降低飞机燃气涡轮发动机上钛合金叶片及叶盘等组件的使用寿命。为对钛合金进行合理的成分及工艺设计以提高叶片及叶盘等组件的使用寿命，亟需了解钛合金保载疲劳敏感性的成分及温度依赖性的机理及规律。根据保载疲劳的Stroh位错堆积模型，本项目提出钛合金保载疲劳成分及温度依赖性决定于成分及温度对密排六角结构alpha相位错滑移临界剪切应力及其各向异性的影响。基于这一设想，拟采用第一原理方法计算alpha相各滑移系广义层错能随成分及温度的变化，进而采用离散变分P-N模型计算各滑移系位错运动临界剪切应力，系统研究合金成分及温度对alpha相位错运动临界剪切应力及其各向异性的影响，揭示其电子结构机理及规律性；结合实验测量得到的钛合金保载疲劳敏感性数据，建立成分/温度与保载疲劳敏感性间的关系模型，为低保载疲劳敏感性钛合金的设计提供理论基础。

Dwell fatigue of titanium alloys reduces significantly the life-time of the blades and disks of gas turbine engine in a jet aircraft. The dwell fatigue susceptibility of titanium alloy depends highly on the alloy composition and temperature. Understanding the mechanisms and determining the regularities underlying such dependences are demanded for the rational design of the composition and process of titanium alloys so as to improve the service life-time of the blades and disks. According to the Stroh dislocation pile-up model of the dwell fatigue, we consider that the composition and temperature dependences of the dwell fatigue are mainly determined by the effects of the composition and temperature on the anisotropy of the critical shear stress (CSS) for the dislocation glide in the hcp alpha-titanium phase. In this regards, we propose to investigate the influences of composition and temperature on the CSS and its anisotropy and to explore the underlying mechanisms and regularities in the project. This will be achieved by calculating the generalized stacking fault energies (GSFEs) of various slip systems of alpha phase against the composition and temperature using accurate first-principles methods. The CSSs are then evaluated with the GSFEs by using the semi-discrete variational P-N model. Together with the experimentally measured dwell fatigue susceptibility, the calculated CSSs will be adopted to establish a predictive model of the dwell fatigue susceptibility against the alloy composition and temperature, which will hopefully help the design of titanium alloys with low dwell fatigue susceptibility.