Effects of reinforcement volume fraction on tensile behaviors of laminated Ti-TiBw/Ti composites

A range of laminated Ti-TiBw/Ti composites composed of Ti layer and TiBw/Ti composite layer with different volume fractions of TiB whisker (TiBw) were successfully fabricated by diffusion welding. TiBw reinforcement exhibits different morphologies, such as needle-like, self-joining, claw-like and cluster structures due to the increasing volume fractions of TiB. The elastic modulus and yield strength of the laminated composites with different volume fractions of TiB are consistent with the HT equation and shear lag model, respectively. The ultimate tensile strength of the laminated composites with 5 vol%, 8 vol%, 10 vol% and 12 vol% TiBw/Ti composite layer is 604 MPa, 689 MPa, 744 MPa and 789 MPa, along with tensile elongation of 19.7%, 14.1%, 10.4% and 5.5%, respectively. The fracture characteristics of the laminated composites reveal a ductile to brittle transition (DBT) behavior with the increase of TiB volume fraction: fractograph in TiBw/Ti composite layer changes from tortuous into flatter, and Ti layer changes from ductile fracture accompanying with many dimples into brittle fracture with many lath-like fracture morphologies, which are attributed to the decreasing size of plastic zone at the tunnel crack tip.