Impact of plastic strain amplitude on the cyclic behavior of commercially pure titanium grade 2

• Published in: International journal of fatigue Vol. 182; p. 108192
• Main Authors: Moreira, L.C.M., Radi, A., Oudriss, A., Berziou, C., Cohendoz, S., Lotte, G., Frappart, S., Mathis, A., Millot, T., Bouhattate, J., Feaugas, X.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.05.2024; Elsevier
• Subjects: Crack initiation and propagation; Dislocation and twinning features; Engineering Sciences; Fatigue; Internal stresses; Titanium alloys; Titanium alloys; Fatigue; Dislocation and twinning features; Crack initiation and propagation; Internal stresses
• ISSN: 0142-1123; 1879-3452
• DOI: 10.1016/j.ijfatigue.2024.108192

•Oxygen distribution disorder arises due to the shearing of precipitates during fatigue, and the existence of a cluster of vacancies results in a reduction of effective stress in relation with the possible oxygen trapping process.•Transition from a dipolar dislocation structure to a polarized cell’s structure in polycrystalline α-titanium alloys when increasing plastic strain amplitude.•Stereographic analyses reveal that the initiation of cracks takes place within a twin plane.•A comprehensive examination of striation has been conducted across various levels of plastic strain amplitude to assess crack growth speed, correlated with the size of dislocation cells. The present study focuses on investigating the impact of plastic strain amplitude on the mechanical behavior of T40 (Grade 2) under low cycle fatigue (LCF) at room temperature with a strain rate of 2 × 10−3 s−1. The mechanical behavior is analyzed in terms of effective and back stress evolution, and the relationship between the microstructural observations, based on analyses using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The evolution of stress amplitude as a function of cyclic number highlights a competition between hardening and softening processes. Both effects can be related to a specific evolution of internal stresses with dislocation patterns and dislocation/oxygen interactions. Crack initiation and propagation regimes are studied using the measurement of striation spacing and TEM-FIB samples on the crack surface. Crack initiates along (10–12) twins and propagates with a crack growth rate directly proportional to the dislocation inter-wall spacing.