High fatigue performance and microscopic mechanisms of in-situ TiB₂/7050Al composite at different temperatures

In this work, the fatigue properties of in-situ TiB₂ particle-reinforced 7050 Al-matrix (TiB₂/7050Al) composites at room temperature (RM), 100 ℃ and 150 ℃ were studied, respectively, and the microstructure changes, fatigue fracture characteristics and fracture mechanism were analyzed. The results indicate that when the fatigue temperature increased, the amount of S phase precipitation along grain boundaries increases, forming a banded distribution with TiB₂ particles near the grain boundary regions. The RM fatigue limit of the composite is high up to 307.5 MPa. Under the same fatigue strength, TiB₂/7050 composites can withstand fatigue cycles far greater than 7050Al alloy. With the increase of temperature, the fatigue performance of the composite gradually decreased, and unlike at RM and 100 ℃, the use of Weibull three-parameter model is necessary to obtain a satisfactory S-N curve at 150 ℃. In some locations of the steady-state crack propagation stage, the direction and spacing of fatigue striations were influenced by grain orientation, grain boundaries and TiB₂ particle bands. Therefore, the effects of TiB₂ particles, grain boundaries, and precipitations on the fatigue processes were analyzed to reveal the strengthening mechanisms of the composite.