An interesting phenomenon of dual S-N fatigue behavior is investigated in a metastable β titanium alloy, Ti-7Mo-3Nb-3Cr-3Al notched cylindrical specimens with an elastic stress concentration factor of K_t = 3. Fractographic studies revealed all specimens, and irrespective of lifetime, failed from the specimen surface because of stress concentration occurs at the notch root. Typically, the short-life-distribution is usually associated with surface-failure-without-facets and the long-life-distribution generally occurs due to surface-failure-with-facets. This competing failure leads to increasing the variability in fatigue lifetime and further facilitates the difficulty in prediction of fatigue lifetime. Crack-initiation area characterization was conducted by using mechanical grinding, focused ion beam milling and subsequent electron back-scattered diffraction (EBSD) analysis of the 2D section across faceted grains. Results show that the α_p particles (especially the elongated α_p particles) well-oriented for basal slip activation is a preferential fatigue-critical microstructural configuration. Additionally, the β+α_s matrix has a higher KAM value than the α_p particles in fatigued microstructures and significant dislocation activity in the form of dislocation tangles is observed in α_p boundaries.

双重的一个有趣的现象小号- ñ处于亚稳β型钛合金的疲劳特性进行了研究，的Ti-7Mo-3NB-3CR-3AL缺口圆柱形试样用的弹性应力集中系数ķ_吨=3。分形研究表明，由于应力集中在缺口的根部，所有标本，无论寿命长短，均从标本表面失效。通常，短寿命分布通常与无面的表面故障有关，而长寿命分布通常是由于具有小面的表面故障而发生的。这种竞争性失效导致疲劳寿命的可变性增加，并且进一步促进了疲劳寿命的预测困难。通过使用机械研磨，聚焦离子束铣削和随后的多面晶粒二维截面的电子背散射衍射（EBSD）分析，进行了裂纹起始区域的表征。结果表明，α _p颗粒（尤其是细长的α _p取向良好的基底滑移激活是一种优先考虑的疲劳关键型微观结构。另外，+α的β_小号基质具有更高KAM值比α _p在疲劳的微观结构和位错缠结的形式显著错位活性颗粒在α观察到_p边界。