臺灣博碩士論文加值系統

雙相鈦合金Ti-6Al-4V 與 β-rich SP700為本論文之主要材料。兩種材料具有相近的機械性質，於本論文中，將分別比較兩種鈦合金在500℃及100 MPa下的高溫變形潛變行為及鑽石鍍膜對銲接殘留應力之影響。
本論文研究發現β-rich SP700的抗潛變性較Ti-6Al-4V 優越。在經過160個小時潛變後β相之體積分率增加5%，而負潛變則相對只增加2%。在應力遽降後之潛伏期間(incubation period)其晶粒會成長且此時之晶粒尺寸會大於定應力潛變。穩態潛變為造成動態再結晶的細晶粒消散於變形晶粒基質中主要成因。
此研究以實驗與模擬兩種鈦合金於相同輸入熱下的銲接殘留應力分佈。Ti-6Al-4V有較SP700大的殘留張應力歸因於較低的熱傳導係數、熱擴散係數及相對較高的熱膨脹係數。有限元素模擬結果皆與量測實驗值相符。以陰極電弧鍍DLC鑽石薄膜於銲接過的鈦合金板材上，會降低及釋放某種程度上的銲接殘留應力。

Two kinds of duplex titanium alloys, Ti-6Al-4V and β-rich SP700, are investigated in this research. The high temperature deformation of creep of both titanium alloys and under 500℃ and 100 MPa are investigated in this research. The effect of DLC on welding residual stress is another topic of this research.
The creep resistance of β-rich SP700 is superior to that of Ti64. The volume fraction of the β phase shows a 5% increase for 160 hours of creep, in contrast to a 2% increase for negative creep. The grain growth occurs during the stress drop incubation period, and the grain size is larger than that of constant creep. The dynamic recrystallized fine grains dispersed in the matrix of deformed grains are attributed to the steady creep.
The distribution of welding residual stress in Ti64 and SP700 alloy plate are measured and calculated under the same heat input. Ti64 alloy exhibits a higher residual tensile stress than the SP700 alloy due to the low thermal conductivity and thermal diffusivity of the Ti64 alloy in addition its high thermal expansion coefficient. The simulation results correspond to the measurements. Diamond like carbon (DLC) thin film deposited on the as-welded titanium alloy plates reduces and relaxes the magnitude of welding residual stress by using the cathodic arc PVD process

Chapter 1 Introduction 1
Chapter 2 Literatures Review 3
2.1 Properties of titanium alloys Ti-6Al-4V and SP700 3
2.2 Creep behavior of titanium alloys 7
2.3 Diamond like carbon (DLC) coating and welding residual stress 10
Chapter 3 Experimental procedures 17
3.1 Materials 17
3.1.1 Round bar for creep test 17
3.1.2 Thick plate for welding 17
3.2 Tensile test 18
3.3 Creep test 20
3.4 Optical microstructure observation 22
3.5 SEM microstructure observation 22
3.6 TEM microstructure observation 22
3.7 pulsed gas tungsten arc welding 25
3.8 welding thermal cycle measurement 27
3.9 Residual stress measurement 27
3.10 DLC coating 29
Chapter 4 Results and Discussion 30
4.1 The creep and stress-drop incubation behavior of titanium alloys Ti-6Al-4V and SP700 30
4.1.1 The optical microstructure of as-received Ti64 and SP700 30
4.1.2 The creep behavior of Ti64 and SP700 31
4.1.3 The volume fraction change in Ti64 and SP700 33
4.1.4 High resolution microstructure observation of crept Ti64 and SP700 34
4.2 Diamond like carbon (DLC) films relaxing the welding residual stress for duplex titanium alloys 51
4.2.1 The residual stress distribution of Ti64 and SP700 weld 51
4.2.2 Stress released by DLC coating on the Ti64 and SP700 weld 53
Chapter 5 Conclusions 63
References 65
Vita 70

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