Compressive behaviors and mechanisms of TiB whiskers reinforced high temperature Ti60 alloy matrix composites

The hot deformation behaviors of TiB whiskers reinforced Ti60 alloy matrix composites with network microstructure were investigated by hot compression tests in the temperature range of 900-1050 °C and strain rate range of 0.001-1 s−1. The flow stress curves exhibited obvious flow softening phenomenon at low strain rates in the α+β phase region, which was mainly attributed to the globularization of α phase. The apparent activation energy of the composite was calculated to be 681 kJ/mol in α+β phase region, which is much higher than that of Ti60 alloy due to the network distribution of TiBw reinforcement. The constitutive equation for the composites in α+β phase region was also established. The processing maps of the composites exhibit one peak efficiency of power dissipation at 950 °C/0.03 s−1 about 57%, which corresponded to globularization or dynamic recrystallization of lamella α phase. The equiaxed α grain preferably formed at TiBw-rich region (network boundary), which indicated that the TiBw can promote globularization of lamella α phase. In the instability region, inhomogeneous deformation and macroscopic crack can be observed. Additionally, the EBSD results reveal that the large equiaxed α grains contain lots of low angle grain boundaries (LAGBs), which indicates that globularization of lamella α phase is attributed to the continuous dynamic recrystallization (CDRX) mechanism. In single β phase region, the fraction of LAGBs is decreased with decreasing the strain rates, which indicates that DRX of β phase occurs at low strain rate.