本文主要是利用霍普金森扭轉試驗機來研究鎳基718超合金受動態剪切荷載下之塑性變形與破壞行為。扭轉試片分別於溫度-150℃ 、25℃ 、300℃及應變速率1×103 s-1、1.5×103 s-1、3.2×103 s-1條件下進行剪切變形測試。藉由巨觀性質與破壞特性來探討應變與應變速率兩者於動態剪切變形下對材料塑變行為之影響與關係；並引用一構成方程式來描述鎳基718超合金於高速動態剪切行為。
實驗結果顯示鎳基718超合金機械性質受剪應變速率、溫度及剪應變量之影響甚鉅，在固定溫度條件下，其塑流剪應力值、破壞剪應變量、加工硬化率、降伏剪強度、加工硬化係數、應變速率敏感性係數與溫度敏感性係數皆會隨著剪應變速率的提升而增加，而活化能則隨應變速率增加而減少；另外，在固定剪應變速率條件下，其塑流剪應力值、加工硬化率、降伏剪強度、加工硬化係數、應變速率敏感性係數、與溫度敏感性係數皆會隨著測試溫度的提高而下降，而破壞剪應變量與活化能則隨著溫度的提高而增加。藉由Kobayashi & Dodd模式之構成方程式能準確地描述鎳基718超合金在不同溫度及應變速率下的剪切塑變行為。而掃描式電子顯微鏡(SEM)與光學顯微鏡(OM)之破壞形貌與金相組織分析顯示，破斷面韌窩形貌隨應變速率與溫度的提高，有越來越密且深的趨勢；而破斷區域之金相組織隨溫度與應變速率的增加，其破斷面處晶粒扭曲更加劇烈，且塑性變形區域有越來越擴大之趨勢。

A split-Hopkinson torsional bar system is employed to conduct a comprehensive investigation into the dynamic shear deformation behaviour and fracture characteristics of Inconel 718 superalloy. The investigations commence by examining the mechanical response of the alloy under shear strain rates of 1×103 s-1, 1.5×103 s-1and 3.2×103 s-1, respectively, at temperatures of -150℃, 25℃ and 300℃.
The experimental results indicate that the shear strain, shear strain rate and temperature all have a significant influence on the mechanical properties of Inconel 718 superalloy. For a constant temperature, the flow shear stress, fracture shear strain, work hardening rate, yielding shear strength, work hardening coefficient, strain rate sensitivity and temperature sensitivity all increase with increasing strain rate, while the activation energy decreases. Conversely, for a constant strain rate, the flow shear stress, work hardening rate, yielding shear strength, work hardening coefficient, strain rate sensitivity, temperature sensitivity all decrease with increasing temperature, while the fracture shear strain and activation energy increase. The fracture surfaces are characterized by a dimple-like structure, which is indicative of a ductile failure mode. The appearance and density of these dimples are strongly related to the applied strain rate and temperature conditions. Optical microscopy observations reveal that grain structure of the fracture surfaces are twisted most severely. It is found that the high strain rate shear plastic behaviour of Inconel 718 superalloy can be accurately predicted using the Kobayashi and Dodd constitutive equation.

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