保载效应从近alpha型钛合金（如Ti6242）到近beta型钛合金（如Ti6246）会发生由强到弱的转变，并伴随着塑性应变累积降低，疲劳裂纹数量变少等特征，控制其转变的主导因素和机制目前尚不明确。本项目将基于Ti6242和Ti6246合金中初生alpha相（或alpha晶粒）的化学成分，分别单独制备合金，并根据需要增设对比实验，以研究alpha晶粒尺寸、化学成分以及应变速率对alpha钛合金保载效应的影响。重点考察保载疲劳条件下位错平面滑移行为，表征滑移带间距和厚度。探寻位错平面滑移特征与保载疲劳塑性应变累积、裂纹萌生以及疲劳寿命之间的关系，阐明保载效应影响因素和机制。通过以上研究结果为提升钛合金产品性能，解决制约其工程应用的室温蠕变和保载疲劳问题提供新思路。

From near alpha titanium alloys (eg. Ti6242) to near beta titanium alloys (eg. Ti6246), the dwell effect has a transition from strong to weak, accompanying with the decreasing of plastic strain accumulation and the number of fatigue cracks, however, the dominant factor and specific mechanism accounted for the above transition are still not fully understood. This project would concentrate on the influence of alpha grain size, chemical composition and strain rate on the dwell effect of alpha titanium alloys, which are prepared basing on the chemical composition of primary alpha phases in Ti6242 and Ti6246 alloys. The research emphasis would be placed on characterizing the planar slip behavior including the spacing and thickness of planar slip bands. Moreover, the relationship between the planar slip characteristics and plastic strain accumulation, fatigue crack initiation and fatigue life would be explored. A deeper understanding of the influencing factors of dwell effect and the underlying mechanisms would help to provide new ideas for improving the properties of titanium products and solving the problems, i.e., room temperature creep and dwell effect, which restricted their industry application.