针对我国商用航空发动机大尺寸Ti6242合金压气机盘，开展了峰值应力对其室温保载效应影响的研究。利用Basquin方程式拟合了疲劳寿命与应力的关系，获得了保载效应应力门槛值。采用OM、SEM、XCT、EBSD和TEM等表征和分析了Ti6242合金保载效应强弱变化的失效特征及微观机制。结果表明，保载疲劳易于促使Ti6242合金形成稠密的位错平面滑移带，滑移带易穿越次生α相(α_s)片层，形成长距离滑移；增加应力会使裂纹萌生所需的晶体学条件放宽，使得软、硬晶粒分别在不利角度下启动位错滑移并解理开裂，形成空间取向角范围更大的解理小平面以及更多的疲劳裂纹，并开动难滑移的<c + a>位错和锥面滑移。利用XCT技术量化表征保载疲劳二次裂纹，间接测得Ti6242压气机盘中微织构的平均尺寸约为72 μm。根据断口小平面空间取向角结果，提出了基于EBSD数据识别适于反映保载疲劳性能的特征组织参数方法。

Cold dwell-fatigue failure in titanium components of gas turbine engines has been a concern for over five decades, posing a continuous threat to the safe operation of aircrafts. Owing to the complexity of influencing factors and mechanisms, there has been a lack of complete understanding and effective prevention of cold dwell effect. In this study, the effects of peak stresses on the dwell effect at room temperature were investigated, focusing on a large compressor disc manufactured from Ti6242 alloy, specifically designed for use in commercial aeroengines in China. The relationships between fatigue life and peak stress were fitted by the Basquin equation, and the stress threshold value of cold dwell effect was obtained. A detailed characterization of the fatigue failure characteristics and microscopic mechanisms was performed using OM, SEM, XCT, EBSD, and TEM techniques. The results revealed a progression of dwell fatigue-fracture characteristics in Ti6242 alloy as the peak stress increased from near-threshold value of the dwell effect to the value exceeding the yield strength. The failure characteristics included initiation of surface crack, mixed surface and subsurface crack, subsurface crack, and mixed subsurface crack and tensile dimples. Initiation facets formed due to dwell fatigue loading exhibited decreasing spatial angles with increasing peak stress levels in the range of ~20^o-44^o for the stress levels studied. However, the spatial orientations of the propagation facets formed due to dwell fatigue loading were unaffected by the peak stress and remained at less than ~20^o. Dwell fatigue stimulated the formation of dense dislocation planar slip bands, facilitating their transfer across the secondary α (α_s) lamellae and eventually resulting in long-distance slips. Increasing stress further relaxed the crystallographic conditions necessary for the crack initiation, leading to dislocation sliding and cleavage cracking in unfavorably oriented soft and hard grains. Consequently, at higher stress levels the cleavage facets exhibited a larger spatial orientation range, accompanied by the formation of more fatigue cracks. In the case of dwell fatigue, high-stress levels activated <c + a> dislocations and pyramidal slips. The size and number of fatigue cracks were related to the peak stress. Quantitative characterization of secondary cracks in the dwell fatigue specimens using XCT indirectly showed the average size of macrozones in Ti6242 compressor disc to be approximately 72 μm. The Ti6242 compressor disc exhibited a relatively strong texture, featuring a <\mathrm{11}\overline{\mathrm{2}}\mathrm{0}> partial fiber along the axial direction and a <0001> partial fiber aligned with the radial and transverse directions. Based on the spatial orientation of facets on the fracture surface, a method using EBSD data to identify a microstructural feature parameter indicative of dwell fatigue performance was proposed, i.e., the cluster size of α grains with the c-axes inclined within ~30° to the loading direction.