钛合金α相<c+a>方向变形机制的第一原理研究

钛合金发动机叶片及叶盘使用过程中出现的保载疲劳现象显著降低其使用寿命。保载疲劳源于钛合金密排六角结构α相塑性变形的强烈各向异性，即，锥面<c+a>方向变形能力低于基面及柱面<a>方向。增加<c+a>方向的变形能力是降低保载疲劳敏感性的根本途径。<c+a>方向可能的变形机制为直线位错滑移、双扭折位错滑移及孪晶变形，具体变形机制及变形能力随成分、温度的变化仍不明确。本项目拟采用第一原理方法计算α相<c+a>型直线位错滑移、双扭折位错滑移及孪晶变形的临界分切应力，研究合金成分及温度对临界分切应力的影响及规律，通过比较不同变形机制的临界分切应力，确定不同成分、温度及应力加载方向下的具体变形机制及变形能力，为调控成分及温度以降低合金的保载疲劳敏感性提供理论基础。

Dwell fatigue remarkably reduces the life time of the titanium blades due to the deformation anisotropy for α phase (HCP) with low symmetry, i.e., the <c+a> deformation is harder than <a> deformation. The deformability along <c+a> direction is crucial to decreasing the dwell fatigue susceptibility. The possible deformation mechanisms include the slipping of straight dislocations, double kinked dislocations and twinning, with the influence of composition and temperature still unclear. We propose to calculate the critical resolved shear stresses (CRSS) of <c+a> straight dislocation, double kinked dislocation and twinning in α phase using first principles methods, and study the effect of alloying and temperature. The calculated CRSS are then adopted to determine the mechanism and capability of <c+a> deformation at different temperatures and compositions. Establish a model of the deformation mechanism and CRSS against composition and temperature to provide the theoretical basis for decreasing the dwell fatigue susceptibility through the composition and temperature regulate.