High cycle fatigue fracture mechanism of in-situ TiB₂/7050Al matrix composite

During the service of TiB₂/7050 aluminum-matrix composites, high cycle fatigue (HCF) is the main failure mode, so it is crucial to study the HCF fracture mechanism of the composites. In this work, the room-temperature HCF performance and fatigue fracture mechanism of the in-situ synthesized submicron TiB₂ particle reinforced 7050 Al-matrix composites were studied. The results indicate that, when the stress ratio R = −1 and the specified fatigue fracture life is 3 × 10⁷ cycles, the conditional fatigue strength of the composite is 220 MPa, which is much higher than the matrix 7050 aluminum alloy. The reason why the addition of TiB₂ improves the fatigue properties of the material is attributed to two aspects: the refinement of the matrix grains, and the significant increase in dislocation density in the matrix caused by the difference in elastic modulus and thermal expansion coefficient between the reinforcement and the matrix. By analyzing the microstructure parameters of the longitudinal section near the fracture surface of fatigue specimens, it is found that the grain orientation, dislocation density near the crack source, Schmid factor, and Taylor factor have the most significant correlations with the magnitude of stress levels.