Effects of stress state, strain rate, and temperature on fracture behavior of in situ TiB2/2024 Al composite

To gain insights into the relationship between the fracture behavior and the unique microstructure of the in situ TiB2/2024 Al composite, systematic experiments were conducted over wide ranges of temperature (298–673 K), strain rate (0.001–4000/s), and stress triaxiality (−0.82–1.03). The results showed that the strengthening mechanism of the composite was related to Orowan strengthening and coefficient of thermal expansion (CTE) mismatch strengthening. Owing to the smaller particle size and sturdy interfacial bonding, the tensile strength of the in situ nano/submicron TiB2/2024 composite was higher than that of the ex situ composite and the in situ micron composite. Through a morphologic study by scanning electron microscopy (SEM), the microstructural deformation and crack propagation path were found to be largely dependent on the stress state, strain rate, and temperature. The melted matrix precipitated in the dynamic tensile fracture surface can hinder the crack propagation and is considered the determining factor that improves the ductility at room temperature. Furthermore, a 3D fracture locus in the space of the fracture strain, stress triaxiality, and the Lode angle parameter was formed. Finally, a new fracture criterion that considers the Lode angle parameter, the stress triaxiality cutoff value, and the coupling effect of strain rate and temperature was developed. The developed criterion exhibited a robust and accurate capability to describe the fracture behavior of the in situ TiB2/2024 Al composite.