- 期刊
Dynamic Flow Behaviour and Microstructural Evolution of Pure Titanium during Hot Deformation
純鈦在熱變形下之動態變形行為與微觀結構分析
摘要
The dynamic flow behaviour and microstructural evolution of pure titanium are investigated at strain rates of 1x10^3 s^(-1), 3x10^3 s^(-1) and 5x10^3 s^(-1) and temperatures of 25℃, 400℃, 800℃ and 1000℃ using a compressive split-Hopkinson pressure bar (SHPB) system. The results show that the flow stress, strain rate sensitivity, temperature sensitivity and work hardening coefficient increase with increasing strain rate or decreasing temperature. In addition, it is shown that the flow behaviour of pure titanium can be adequately described using the Zerilli-Armstrong hcp constitutive equation. Transmission electron microscopy observations reveal that the dislocation density decreases with increasing temperature or decreasing strain rate. The loss of flow resistance under elevated deformation temperatures can be attributed to a greater annihilation rate of the dislocations. Finally, the flow stress increases linearly with the square root of the dislocation density and obeys the Bailey-Hirsch relationship.
並列摘要
純鈦具有優異的機械及生醫性能，已被廣泛應用在航太與醫學植入材之應用。本研究利用哈普金森高速撞擊試驗機，研究純鈦在熱變形下之動態塑變行為與微觀結構特徵。變形時應變速率控制在1x10^3～5x10^3 s^(-1)之間，溫度則為25～1000℃的範圍。結果顯示，純鈦之流變應力、加工硬化率、應變速率敏感性係數與溫度敏感性係數皆隨應變速率的增加而增加，但隨溫度的上升而降低。實驗所得之塑性變形行為可藉Zerilli-Armstrong hcp 組構方程來準確的描述。差排結構分析顯示，差排密度隨應變速率的增加而增加；但隨溫度的上升而降低。其流變阻抗的降低可歸因於差排隨溫度的快速衰減所致。而流變應力與差排密度呈線性關係， 並遵循Bailey-Hirsch的關係。