臺灣博碩士論文加值系統

　　本研究主要是利用霍普金森高速撞擊試驗機，討論燒結密度對316L不�袗�粉末冶金件撞擊性能的影響。實驗中，各密度試件之製程參數由田口式分析法設計；而撞擊試驗過程於25℃進行，將相對密度93%、88%及83%試件於應變速率3×103 s-1、5×103 s-1、7×103 s-1、9×103 s-1下進行衝擊試驗，再將所得數據及微觀結果(OM、SEM)進行分析，以釐清燒結密度及應變速率對動態荷載下之塑性變形行為及微觀組織的影響。並於最後引用一材料構成方程式來描述316L不�袗�粉末冶金件於各燒結密度及應變速率條件下之塑變行為，以做為工程模擬分析之用。

　　研究結果顯示，316L不�袗�粉末冶金件之動態機械性質受到燒結密度及應變速率的影響甚鉅。針對相同密度的試件而言，其塑流應力及應變速率敏感性係數皆隨著應變速率的增加而上升，熱活化體積及加工硬化係數則呈現相反的趨勢；而在同一應變速率下，塑流應力值及應變速率敏感性係數隨燒結密度的增加而上升，而熱活化體積及加工硬化係數則隨燒結密度的增加而下降。最後，將各實驗條件下之塑流應力值在轉換為von Mises微觀等效應力後，藉由Khan-Huang-Liang模式之構成方程式並加入理論溫升量的修正項，可以很準確的用來描述各密度之316L不�袗�粉末冶金件於高速撞擊下之塑變行為。

　　由破壞形貌觀察，可知316L不�袗�粉末冶金件在高速變形下，破壞的模式由絕熱剪切帶主導，材料的破壞乃由主裂縫及次裂縫之絕熱剪切帶相互結合而成；另於壓縮過程中，在試件外緣之圓周表面處亦因孔洞聚集，使材料表面延性降低而導致表面裂縫的出現。其中，材料之主裂縫分佈與應變速率有關，而試件的密度則對於材料的表面延性有直接的影響。此外，在破斷面的觀察上，可以發現主要是以韌窩組織形貌為主的延性破壞形貌，而韌窩組織的形貌亦會隨著燒結密度及應變速率條件而有所不同。

　　This study uses the split-Hopkinson pressure bar to investigate the influence of sintering density on the dynamic impact properties of Type 316L sintered stainless steel. The Taguchi method is used to design the sintering process factors such that the sintered specimens have densities ranging from 83% to 93%. Mechanical testing is performed under strain rates between 3×103 s-1 and 9×103 s-1. OM and SEM microscopy techniques are used to analyze the fracture and microstructural characteristics of the deformed specimens to determine the relationship between the mechanical and microstructural properties. The experimental results show that the sintering density, strain and strain rate all influence the mechanical properties of the Type 316L stainless steel. At a constant sintering density, the flow stress and strain rate sensitivity increase with increasing strain rate, but the activation volume and work hardening coefficient decrease. Under a constant strain rate, the flow stress and strain rate sensitivity increase with increasing sintering density, while the activation volume and work hardening coefficient decrease. Fractographic analysis reveals that the crack distribution depends strongly on the strain rate and shows that the surface ductility decreases with decreasing sintering density. The OM and SEM fracture feature observations indicate that adiabatic shear band formation is the dominant fracture mechanism. The shear bands form along the direction of maximum shear stress. Furthermore, dimple characteristics are observed on the fracture surfaces. The depth and density of the dimples are found to decrease as the strain rate is increased. Finally, applying the Khan-Huang-Liang constitutive equation with the experimentally determined specific material parameters provides accurate predictions of the flow behaviour of Type 316L sintered stainless steel under the current test conditions.

中文摘要 I
ABSTRACT II
誌謝 III
總目錄 IV
表目錄 VIII
圖目錄 X
符號說明 XVIII

第一章 前言 1

第二章 理論與文獻回顧 4
2-1 不�袗�概述 4
2-2 粉末冶金製程 5
2-2-1 粉末整備 5
2-2-2 鋼模冷壓成形技術 6
2-2-3 粉末燒結 7
2-2-4 影響316L不�袗�粉末冶金件性質之參數 8
2-3 動態塑性變形相關理論 10
2-3-1 塑性變形機構 10
2-3-2 塑性變形行為之機械測試類別 13
2-3-3 一維波傳理論 14
2-3-4 霍普金森桿之原理 16
2-4 孔隙材料之塑性變形 18
2-4-1空孔對材料機械性質的影響 19
2-4-2微觀及巨觀性質 20
2-5 材料變形構成方程式 21
2-6 田口式品質設計法 23
2-6-1 田口式直交表 23
2-6-2 信號雜訊比 24
2-6-3 變異分析 24

第三章 實驗方法與步驟 34
3-1 試件製備 34
3-1-1 製程參數設計 34
3-1-2 粉料性質與整備 38
3-1-3 粉末加壓成形 38
3-1-4 生胚燒結 38
3-1-5 後加工處理 39
3-2 實驗儀器與設備 39
3-2-1 粉末成形油壓機 39
3-2-2 混粉機 39
3-2-3 燒結氣氛爐 40
3-2-4 霍普金森動態撞擊試驗機 40
3-2-5 訊號處理裝置 41
3-2-6 壓縮試驗機 41
3-2-7 微小硬度試驗機 41
3-2-8 光學顯微鏡(OM) 41
3-2-9 掃描式電子顯微鏡(SEM) 41
3-3 實驗方法與步驟 42
3-3-1 動態衝擊實驗 42
3-3-2 靜態壓縮試驗 43
3-3-3 金相觀察(OM) 43
3-3-4 破斷面觀察(SEM) 44

第四章 實驗結果與討論 54
4-1 應力-應變曲線圖之討論 54
4-2 加工硬化之討論 55
4-3 應變速率效應 56
4-4 熱活化體積 58
4-5 理論溫升量 59
4-6 材料構成方程式 60
4-7 材料整體破壞形貌觀察 63
4-7-1 主破壞機構 63
4-7-2 鼓脹區之表面裂縫 64
4-8 金相組織觀察 65
4-8-1 端面及縱剖面金相組織 65
4-8-2 絕熱剪切帶 66
4-9 SEM破壞形貌分析 68
4-9-1 圓周表面之絕熱剪切帶 68
4-9-2 破斷面組織分析 69

第五章 結論 138

參考文獻 140

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