本論文主要是利用霍普金森高速撞擊試驗機並配合低溫裝置，來研究Ti-6Al-4V合金在低溫高應變速率下之塑性變形行為，訂溫度-150℃、0℃和25℃以及應變速率1000 s-1、3000 s-1和4300 s-1為實驗之條件，之後分析實驗所得之數據，並與微觀觀察(OM、SEM、TEM)做比較，以獲取兩者間之關連性。
　　實驗結果顯示，溫度與應變速率對Ti-6Al-4V合金的機械性質影響甚鉅。在相同溫度條件下，其塑流應力值、加工硬化率與應變速率敏感性係數均會隨應變速率之增加而上升，但熱活化體積會變小。在相同應變速率條件下，其塑流應力值、加工硬化率與應變速率敏感性係數則會隨溫度之增加而下降，不過熱活化體積會變大。另外，我們可以藉由Combined Johnson-Cook and Zerilli-Armstrong構成方程式，來精確的預測描述Ti-6Al-4V合金的塑性變形行為。
　　由光學顯微鏡觀察，可知Ti-6Al-4V合金中有絕熱剪切帶形成，其寬度隨著應變速率和溫度的上升而增加，而剪切帶中之裂縫生成與結合，正是導致材料破壞的主要原因。從掃描式電子顯微鏡的破壞形貌分析中，可發現大量韌窩組織，表示Ti-6Al-4V合金是屬於延性破壞模式，且在較高的應變速率和溫度下，會有較密且深的韌窩組織。另外，以穿透式電子顯微鏡分析微觀結構，可發覺差排數量會隨著應變速率上升而增加，但隨著的溫度上升，數量反而減少。

　　This study uses a split-Hopkinson bar to investigate the plastic deformation behavior of Ti-6Al-4V alloy at the strain rates of 1000 s-1, 3000 s-1 and 4300 s-1 and the temperatures of -150℃, 0℃and 25℃, respectively. The experimental results indicate that the effects of temperature and strain rate on mechanical properties of Ti-6Al-4V alloy are significant. At constant temperature, the flow stress, work hardening rate and strain rate sensitivity increase with increasing strain rate, but the activation volume decreases. For a constant strain rate, the flow stress, work hardening rate and strain rate sensitivity decrease with increasing temperature, but the activation volume increases. The Combined Johnson-Cook and Zerilli-Armstrong constitutive equation can be used to describe the plastic deformation of Ti-6Al-4V alloy. The error between the predicted flow stress and the measured stress is found to be less than 5%.
　　Optical microscopy (OM) observations reveal that adiabatic shear bands form during the high strain rate deformation of Ti-6Al-4V alloy. The width of shear bands is found to increase with the increase of strain rate and temperature. Microvoid nucleation and growth within the shear bands are evident in the material fracture process. Scanning electron microscopy (SEM) fractographic observations show that the fracture features are characterized by transgranular dimpled structure, indicating that Ti-6Al-4V alloy has an excellent ductility. The density of the dimples increases with increasing strain rate and temperature. Transmission electron microscopy (TEM) observations show that the dislocation density increases with increasing strain rate, but decreases with increasing temperature. Based on the macroscopic analysis and microscopic observations, the correlations between mechanical properties and microstructure were established.

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