銲前預熱及銲後熱處理，對α＋β型鈦合金銲件缺口拉伸強度及衝擊值有很大的影響。將試件預熱至300℃以降低銲件冷卻速率，實驗結果與無預熱銲件比較，整體上預熱銲件相有較粗大的α＋β組織，在經過不同溫度銲後熱處理，預熱銲件也有較低的時效硬化現象，在相同銲後熱處理條件下，預熱銲件有較低硬度值及延性增加之現象，其結果改善了銲件的缺口脆性及衝擊韌性。SP-700銲件經482℃時效後有最大缺口脆性，而Ti-6Al-6V-2Sn銲件則在經593℃時效後有最大缺口脆性。無預熱原始銲件破斷面呈現樹枝狀破裂特徵，隨著預熱及時效溫度上升，樹枝狀破裂隨之消失。預熱試件整體上破斷面有較具延性之特徵，如窩穴破裂較深較大、沿晶破裂減少，晶界剪變程度上升等現象，銲後熱處理溫度升高使的銲件晶界α粗大化，而有晶界滑移及沿晶窩穴破裂產生。

Notched tensile strength (NTS) and impact toughness of Ti-4.5Al-3V-2Fe-2Mo and Ti-6Al-6V-2Sn laser welds, which were subjected to various post-weld heat treatments (PWHTs) with or without preheating, were determined in this work. Ti-4.5Al-3V-2Fe-2Mo weld with the PWHT at 482℃ had lowest NTS among the welds. However, the lowest NTS was found for the Ti-6Al-6V-2Sn weld with the PWHT at 593℃. Preheated at 300oC could effectively reduce the cooling rate of the welds, and enhanced the formation of coarse α + β structures as compared with the non-preheated welds. Meanwhile, the preheated welds showed slower responses to age-hardening during PWHTs than the non-preheated. The decrease in hardness and increase in ductility resulted in the lowered notch brittleness and improved impact toughness of the preheated welds, relative to the non-preheated welds at the same PWHT. For the non-preheated weld in the as-welded conditions, the fracture surface showed little extent of interdendritic separation. Note that interdendritic separation disappeared for the welds with the PWHT or preheating before welding. Preheating of the weld tended to assist ductile fractures with large and deep dimples, reduced extent of intergranular fracture as well as increase in grain boundary shear. Increasing PWHT temperature, the coarsening of grain boundary α was associated withd grain boundary sliding on the fracture surface.

總 目 錄
第一章 前言 1
第二章 文獻回顧 2
2-1.1 鈦之特性與應用 2
2-1.2 鈦之相分類 2
2-1.3 溶質原子對鈦合金的影響 3
2-1.4 鈦合金的分類 4
2-1.5 SP700性質介紹 5
2-1.6 Ti-6Al-6V-2Sn性質介紹 5
2-1.7 鈦及鈦合金銲結特性 6
2-2 雷射原理 7
2-2.1 雷射銲接 7
2-3 預熱(Preheating) 9
2-4 缺口拉伸試驗 10
第三章 實驗設備及方法 17
3-1 實驗材料 17
3-2 雷射銲接 17
3-3 時效熱處理 18
3-4.1 SEM與OM的觀察 18
3-4.2 TEM的觀察 19
3-5 缺口拉伸試驗 19
3-6 衝擊試驗 20
第四章 結果與討論 30
4-1 SP700金相及顯微組織觀察 30
4-2 SP700硬度試驗及缺口拉伸試驗 36
4-2.1 SP700硬度試驗 36
4-2.2 SP700缺口拉伸試驗 36
4-3 SP700衝擊試驗 45
4-4 Ti-662硬度試驗及缺口拉伸試驗 53
4-4.1 Ti-662硬度試驗 53
4-4.2 Ti-662缺口拉伸試驗 53
4-5 Ti-662衝擊試驗 62
第五章 結論 69
第六章 參考文獻 71

表 目 錄

表2-1 鈦合金主要應用[6] 11
表2-2 SP700之化學成份[9] 12
表2-3 SP700之基本物理性質[13] 12
表3-1 本實驗所選用之試片及其熱處理條件 21

圖 目 錄

圖2.1 α相HCP及β相BCC結晶結構[7] 13
圖2.2 β/α相變與Burger vector 關係[7] 13
圖2.3 β/α相變之Burger vector 關係[9] 14
圖2.4 溶質原子與鈦合金相圖之關係[7] 14
圖2.5 Ti-Al相圖[7] 15
圖2.6 雷射Keyhole銲接示意圖[33] 15
圖2.7 Keyhole內雷射多重反射現象 [34] 16
圖2.8 電漿雲幕生成過程示意圖 [38] 16
圖3.1 雷射銲接系統 22
圖3.2 銲接夾具示意圖 23
圖3.3 雷射銲接保護氣罩(Shielding Device)示意圖 23
圖3.4 高真空系統配置圖 24
圖3.5 HITACHI-4800場發射掃描式電子顯微鏡 25
圖3.6 JEOL 2010穿透式電子顯微鏡 25
圖3.7 微電腦萬能拉伸試驗機 26
圖3.8 缺口拉伸試片之取裁位置與詳細尺寸 27
圖3.9 Charpy衝擊試驗機 28
圖3.10 衝擊試片之取裁位置與詳細尺寸 29
圖4.1 SP700銲件巨觀 32
圖4.2 SP700銲件經不同時效溫度處理之顯微組織 33
圖4.3 SP700銲件經不同時效溫度處理之TEM照片 35
圖4.4 SP700銲件經不同時效溫度下硬度變化曲圖 39
圖4.5 SP700銲件經不同時效溫度下缺口拉伸強度變化曲圖 40
圖4.6 SP700銲件缺口拉伸破斷面巨觀 41
圖4.7 SP700預熱銲件缺口拉伸破斷面微觀 43
圖4.8 SP700銲件經不同時效溫度下衝擊值變化曲圖 48
圖4.9 SP700衝擊試驗破斷面巨觀 49
圖4.10 SP700衝擊試驗破斷面微觀 51
圖4.11 Ti-662銲件經不同時效溫度下硬度變化曲圖 56
圖4.12 Ti-662銲件經不同時效溫度下缺口拉伸強度變化曲圖 57
圖4.13 Ti-662銲件缺口拉伸破斷面巨觀 58
圖4.14 Ti-662預熱銲件缺口拉伸破斷面微觀 60
圖4.15 Ti-662銲件經不同時效溫度下衝擊值變化曲圖 64
圖4.16 Ti-662衝擊試驗破斷面巨觀 65
圖4.17 Ti-662衝擊試驗破斷面微觀 67

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