The tensile and fracture toughness properties of a (TiBw + TiCp)/Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe composites after heat treatment

This study investigated the tensile and fracture toughness properties of a new (TiBw + TiCp)/Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe composite subjected to solution treatment at 800 degrees C for 1 h with air cooling followed by aging at 440 degrees C, 480 degrees C, and 520 degrees C for 8 h with air cooling. The composite grains were coarse with distinct boundaries after the solution treatment. As the temperature was increased, alpha(p) merged in triangle boundaries and alpha(s) became finer. The basket two-parallel alpha(s) phase comprised many substructures, which generated many dislocations. Finer alpha(s) corresponded to higher strength and fracture toughness. The ultimate tensile strength and yield strength after the solution treatment decreased by 12.5% and 11.3%, respectively. However, the strength significantly improved after aging heat treatment. The highest ultimate tensile strength of 1521 MPa with a 7.2% elongation was reached after aging at 440 degrees C. The ultimate K-IC value was 65 MPa m(1/2) after aging at 480 degrees C. The (TiBw + TiCp) reinforcements formed a streamline along the deformation direction, which enhanced the strength and fatigue toughness. The reinforcements improves the fracture toughness by hindering crack propagation to extend the expansion path and increase the amount of absorbed impact energy.