Very high cycle fatigue behavior of TC4 titanium alloy: Faceting cracking mechanism and life prediction based on dislocation characterization

• Published in: International journal of fatigue Vol. 190; p. 108640
• Main Authors: Deng, Hailong, Liu, Jie, Kang, Heming, Guo, Yupeng, Song, Liming, Yu, Huan
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.01.2025
• Subjects: Blunting effect; Failure mechanism; Fatigue life prediction; TC4 titanium alloy; Very high cycle fatigue; Failure mechanism; Blunting effect; TC4 titanium alloy; Very high cycle fatigue; Fatigue life prediction
• ISSN: 0142-1123
• DOI: 10.1016/j.ijfatigue.2024.108640

•Interior failure result from α grain cleavage fracture influenced by dislocation slip.•Crack blunting promotes dislocation initiation and movement.•Construct slip cleavage competition failure model based on maximum intensity factor.•Proposed life model considering failure mechanism, crack blunting effect, Kc and R.•Test data verified the accuracy of the life prediction model by maximum defect size. This research analyzes the very-high-cycle-fatigue behavior of TC4 titanium alloy through fatigue tests at R = −1, −0.3, and 0.1. The results show that the S-N curves are all bilinear and exhibit three failure modes as surface slip failure, surface cleavage failure and interior cleavage failure. Transmission electron microscopy analysis reveals the dislocation structure in interior cleavage failure and suggests that the deformation mechanism of faceting cracking involves both anti-phase boundary shearing and stacking fault shearing mechanisms. It concludes that interior failure results from cleavage fracture of α grains due to dislocation slip. Based on the stress intensity factor of the maximum defect, a slip-cleavage competitive failure model was developed by considering factors such as control volume, defect size, external loading, and grain content, with good predictive results. Additionally, on the basis of the failure mechanism and crack propagation rate model, considering the coupled effects of crack tip blunting, stress ratio, Vickers hardness, and material fracture toughness on crack propagation, the crack propagation life prediction model is constructed. The life prediction model is further modified to be more conservative and accurate in predicting life by consideration the maximum defect size, providing important theoretical support and practical guidance for engineering applications.