本研究是利用霍普金森撞擊試驗機，測試AISI 4140合金鋼在不同溫度及應變速率條件下之巨觀機械性質與微觀結構分析。實驗參數為溫度25℃、0℃、-150℃及應變速率2600s-1、4000s-1、5200s-1、6000s-1，分析材料在不同實驗條件下之撞擊塑性變形行為。根據實驗結果顯示，材料之巨觀機械性質會隨著溫度、應變速率、應變量的改變而有所差異。在固定溫度條件下，塑流應力值、加工硬化率、應變速率敏感性係數皆隨著應變速率提升而增加，而熱活化體積則會下降。在固定應變速率條件下，塑流應力值、加工硬化率、應變速率敏感性係數則會隨著實驗溫度下降而上升，熱活化體積則會下降。微觀結構分析部分，OM光學顯微鏡之結果可觀測出回火麻田散鐵組織以及絕熱剪切帶與裂縫形貌，而在TEM穿透式電子顯微鏡下，則有差排結構、微滑移帶、雙晶結構的出現並與實驗條件相關。透過差排密度與塑流應力值之連結，顯示材料之巨觀機械性質以及微觀結構之變化有密切的關係。最後，藉由Zerilli-Armstrong構成方程式，可精準的模擬AISI 4140合金鋼在不同溫度與應變速率條件下之塑性變形行為，並可提供未來產業上的實際應用。

關鍵字 : AISI 4140、霍普金森撞擊試驗機、應變速率、塑流應力、剪切帶、微滑移帶、雙晶

In this study, the split-Hopkinson pressure bar system was used to test the mechanical properties and microstructure analysis of AISI 4140 alloy steel under different temperature and strain rate conditions. The experimental examinations were performed at temperatures of 25℃, 0℃, -150℃ and strain rates of 2600s-1, 4000s-1, 5200s-1, 6000s-1, respectively. The experimental results indicate that the mechanical properties of AISI 4140 alloy steel are related to temperature, strain rate, and strain. Under constant temperature, the flow stress, work hardening rate, and strain rate sensitivity coefficient all increase with the increase of the strain rate, while the thermal activation volume decreases. For a fixed strain rate, the flow stress, work hardening rate, and strain rate sensitivity coefficient increase with the decrease of the temperature, but the thermal activation volume decreases. In the microstructure analysis, the optical microscope(OM) observation shows that both the tempered martensite structure and the crack within the adiabatic shear band are observed. Transmission electron microscope(TEM) observations found that the dislocation structure, micro-slip, and twinning appear on the deformed specimens. The flow stress varies with the square root of the dislocation density in accordance with the Bailey-Hirsch model. Finally, the impact deformation behavior is well described by the Zerilli-Armstrong constitutive equation.

Key words: AISI 4140, split-Hopkinson Pressure Bar, strain rate, flow stress, shear band, micro-slip, twinning.

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