Table 1. The average grain size in the UFG pure titanium samples annealed at different temperatures Annealing temperature (oC) 25 300 400 500 600 Average grain size (μm) 0.1 0.2 0.2 3 7 Microstructural observation showed that the average grain size slightly increased when the annealing temperature was less than 400oC. However, the grain size dramatically increased when the annealing temperature was higher than 500oC, as shown in Fig 3. When the annealing temperature is below 400oC, grain size remains constant; however, the distortion and defects in crystal lattice disappear leading to a decrease of the internal stress. When the annealing temperature was higher than 500oC the recrystallization took place in the deformed UFG pure Ti. As a result, the dislocation density remarkably decreased and well-developed grain growth occurred. Figure 3. Average grain sizes in UFG pure Ti annealed at different temperatures. The effect of annealing temperature on texture in UFG titanium is showed in Fig 4. The XRD curve in the initial UFG pure Ti shows that the highest peak is {0002} as shown in Fig 4(a). With increasing annealing temperature to 500°C, the highest peak becomes {10-10}, as shown in Fig 4(b). It means that the lattice rotation took place in UFG titanium during recrystallization. Figure 4. XRD curves of UFG pure titanium annealed at different temperatures Based on microstructural observation with OM and TEM, it is demonstrated that the microstructure (b) (a)
RkJQdWJsaXNoZXIy MjM0NDE=