本文之研究主要是利用霍普金森高速撞擊試驗機，來探討以田口方法所燒結出之三種不同相對密度Fe-2Ni粉末冶金件於高速撞擊下之塑性變形行為。實驗測試於室溫25℃，以不同的應變速率條件分別為2.5x103s-1、4.0x103s-1、6.0x103s-1及8.1x103s-1下進行。並且利用OM及SEM技術對材料進行微觀分析，更進一步討論應變速率對不同相對密度Fe-2Ni粉末冶金件的動態機械特性及相對微觀組織變化之影響。並引用一合適之材料構成方程式，來描述Fe-2Ni粉末冶金件的常溫高速之塑變行為，以做為工程模擬與分析之用。

　　實驗結果顯示，應變速率、應變量及相對密度對Fe-2Ni粉末冶金件的機械性質影響甚鉅。在相同應變量下，應變速率增加，其塑流應力值、應變速率敏感性係數及理論溫升量隨著應變速率的增加而上升，而加工硬化率及熱活化體積則有相反的趨勢。在相同應變速率下，隨著密度的增加，其塑流應力、應變速率敏感性係數及理論溫升量皆隨著應變速率的增加而上升，而加工硬化率及熱活化體積亦呈相反的趨勢。由微觀組織觀察，來瞭解不同製程條件所燒結出之Fe-2Ni粉末冶金件之微觀組織對整體試件在高應變速率作用下之影響。發現本實驗的三種密度試件，在應變速率超過4.0x103s-1時，會有絕熱剪切帶的破壞形貌產生。絕熱剪切帶的生成表示試件局部溫升量的大量上升，因此可觀察到局部區域有動態再結晶的現象。最後，藉由Khan-Huang-Liang模式之構成方程式，其可以很精確的來描述相對密度85%至95%範圍內之Fe-2Ni粉末冶金件於常溫高速撞擊下之塑變行為。

　This study uses the split-Hopkinson bar to investigate the plastic deformation behaviour of Fe-2Ni sintered alloys under high strain rate loading. The Taguchi method is used to design the sintering process factors such that the Fe-2Ni alloy specimens have different densities. The loading tests are performed at room temperature under strain rates ranging from 2.5x103s-1 to 8.1x103s-1. OM and SEM techniques are used to analyze the microstructureal characteristics of the deformed specimens in order to identify the correlating between the mechanical and microstructural properties of Fe-2Ni sintered alloys with different sintering densities. The experimental results indicate that the mechanical properties of the Fe-2Ni sintered alloys depend significantly on the strain rate, strain and sintering densities. Under constant strain, the flow stress, strain rate sensitivity and theoretical raised temperature increase with increasing strain rate, while the work hardening rate and activation volume decrease. At a constant strain rate, the flow stress, strain rate sensitivity and theoretical raised temperature increase with increasing relative density, while the work hardening rate and activation volume decrease. Microstructural obsernations reveal that the sintering process factors influence the effect of dynamic loading on the microstructures of the sintered alloys. Microstructural analysis reveals that adiabatic shear bands are formed when the strain rate exceeds 4.0x103s-1. The formation of these adiabatic shear bands suggests that localized regions of extremely high temperature are generated. It is observed that the local high temperature causes a dynamic recrystallization effect. Finally, applying the Khan-Huang-Liang constitutive equation with the experimentally determined specific material parameters provides accurate predictions of the plastic flow behaviour of Fe-2Ni sintered alloys with relative densities ranging from 85% to 95% under the current test conditions.

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