Deformation behavior and softening mechanism of TiB reinforced near-α titanium matrix composite during hot compression

Abstract

In order to investigate the plastic workability of TiB reinforced near-α high-temperature titanium matrix composite, 3 vol.% TiB/Ti-6Al-4Sn-10Zr-1Mo-1Nb-1W-0.3Si composite were hot compressed over a temperature range of 850–1100 °C and a strain rate range of 0.01–0.5 s−1. Microstructures of the composite after hot compression were observed by scanning electron microscope (SEM), electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The constitutive equations of this composite were calculated and the processing map was established. The results show that the activation energy of (α + β) phase and β phase region were 758550 J · mol−1 and 220510 J · mol−1, respectively. In the stable regions, equiaxed α phase accounting for a high proportion was formed in the matrix at low temperature and strain rate, and became more obvious with increasing of temperature and stain rate. Whereas, in the unstable region the microstructure is mainly characterized by the debonding of TiB closely associated with strain hardening in the matrix, and incomplete recrystallization of β phase in the β phase region at high strain rate. More specially, softening mechanisms in stable during deformation were different under different parameters. The softening mechanism is dominated by the dynamic recrystallization when the process is about 900 °C/0.1–0.01 s−1, but gradually becoming by periodic competition of dynamic recrystallization and dynamic recovery when the processes is 950–1100 °C/0.1 s−1. This difference is mainly attributed to the decreasing of activation energy of at elevated temperature. Finally, the hot deformation processing parameters are optimized as temperature range of 900–950 °C and strain rate of 0.01–0.1 s−1.

Keywords

• Titanium matrix composite
• Processing diagram
• Softening mechanism
• Dynamic recrystallization
• Dynamic recovery