Microstructural correlated damage mechanisms of the high-cycle fatigued in-situ TiB2/Al-Cu-Mg composite

The damage mechanisms during high-cycle fatigue (HCF) process were systematically investigated in the in-situ TiB2/2024 Al-composite. It is found the HCF endurance limit of in-situ TiB2/2024 Al-composite is similar to 360 MPa, which is much higher than the reported ex-situ particle-reinforced composites (similar to 180-300 MPa). A microstructural-based multistage damage in HCF is identified from fracture surface: Stage I (crack initiation), Stage II (stable crack propagation), and Stage III (ultimate fracture). In Stage I, the (S/theta + TiB2) particles generally act as initiation sites inmost cases. The nano or sub-micron TiB2 particles can homogenize stress and reduce dislocations piling-up at grain boundaries (GBs), impeding the crack nucleation from GBs. In Stage II, the GBs, grain orientations and TiB2 particles are the major factors for the damage behaviors. The GB effects depend on their misorientations, geometries and nearby particles. The crack propagation shows crystallographic characteristics of {100} < 001 >, {111} < 110 > and {111} < 112 >, which have different propagation rates. For TiB2 particles, the complex effects on the HCF damage behavior depend on their size and distribution. Considering the microstructural factors, the HCF damage mechanisms was discussed in detail and an energy model of dislocation slipping for nano or sub-micron particle-reinforced metal composites was proposed. (C) 2017 Elsevier Ltd. All rights reserved.