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Please use this identifier to cite or link to this item: http://ntour.ntou.edu.tw:8080/ir/handle/987654321/13615

Title: Ti-4.5Al-3V-2Fe-2Mo與Ti-6Al-6V-2Sn銲件之高溫缺口拉伸性質研究
Notched Tensile Fracture of Ti-4.5Al-3V-2Fe-2Mo and Ti-6Al-6V-2Sn Welds at Elevated Temperatures
Authors: Chung-Liang Hsu
徐鍾良
Contributors: NTOU:Institute of Materials Engineering
國立臺灣海洋大學:材料工程研究所
Keywords: 鈦合金;缺口拉伸試驗;銲後熱處理
Titanium alloy;Notched tensile test;Post-weld heat treatment
Date: 2009
Issue Date: 2011-06-30T07:24:03Z
Abstract: 本研究主要探討Ti-4.5Al-3V-2Fe-2Mo及Ti-6Al-6V-2Sn母材與經不同時效熱處理之銲件,評估兩種鈦合金在不同溫度環境下其缺口拉伸性質之變化情形。 在室溫、150℃、300℃及450℃環境下,對Ti-4.5Al-3V-2Fe-2Mo、Ti-6Al-6V-2Sn母材及經不同時效熱處理之銲件,進行缺口拉伸試驗,結果顯示,Ti-4.5Al-3V-2Fe-2Mo經704℃/1hr時效之銲件與母材,隨測試溫度的升高,其缺口拉伸強度皆隨之下降及延性增加。銲件經482℃/1hr時效後,試件在室溫下具有高缺口脆性,隨著測試溫度上升,其缺口拉伸強度及延性皆隨之增加。當測試溫度達450℃時,原始銲件呈現高缺口脆性效應,此現象歸咎於試件產生時效硬化所致,而銲件經704℃/1hr時效後,其試件具有較粗大的糾結 (interlock) α+β組織,在高溫450℃環境下其缺口拉伸強度優於帶狀α+β組織的原始母材,而由缺口拉伸破斷面顯示,Ti-4.5Al-3V-2Fe-2Mo母材呈現延性細小窩穴狀破裂,隨著測試溫度的升高,有較大且深的窩穴狀破裂特徵,原始銲件室溫下呈現樹枝狀(interdendritic)破裂,隨著測試溫度升高,沿晶窩穴狀破裂特徵隨之遞增,而704℃/1hr時效之銲件,在室溫下可發現穿晶窩穴狀破裂伴隨著沿晶窩穴狀破裂,並於晶界處產生晶界滑移,隨著測試溫度提升,沿柱狀晶破裂的現象越為減少。相較於Ti-6Al-6V-2Sn母材在室溫下有最大的缺口拉伸強度,但在高溫450℃時,強度則降到最低。當測試溫度超過150℃時,所有銲件之缺口拉伸強度皆隨溫度上升而下降。從缺口拉伸破壞面顯示,Ti-6Al-6V-2Sn原始銲件與經482℃/3hr時效之銲件,主要呈現穿晶窩穴狀破裂特徵,而隨測試溫度的提升,晶界滑移的現象越趨顯著。 針對Ti-4.5Al-3V-2Fe-2Mo母材及經593℃/1hr時效之銲件,進行高溫疲勞裂縫成長試驗,結果顯示,300℃與室溫環境下,母材及銲件呈現大體一致的疲勞裂縫成長特性,而在高溫450℃環境下,其裂縫成長速率有稍微提升的現象。觀察破斷面的型態,在室溫下,母材其破裂特徵為穿晶破裂,而銲件破裂特徵較為粗糙,且顯示了受顯微組織的影響,裂縫在不同晶面上成長形成穿晶破壞,並隨著測試溫度升高,以及△K值的提升,兩者的破裂面有次裂縫生成且越趨粗糙的趨勢。
In this study, the influence of post-weld heat treatments (PWHTs) on the notched tensile properties of Ti-4.5Al-3V-2Fe-2Mo (SP700) and Ti-6Al-6V-2Sn (Ti-662) laser welds at different temperatures were investigated. Notched tensile tests of SP700 and Ti-662 welds with distinct PWHTs were carried out at 150, 300, and 450℃. The results were also compared with those from a mill-annealed base metal (MA) tested at the same conditions. The weld with PWHT at 704℃ and MA specimens exhibited a reduced notched tensile strength (NTS) and an increased ductility with increasing temperatures. In contrast, the weld with PWHT at 482℃ (W-482), which revealed severe notch brittleness at room temperature, showed an increase in strength and ductility as the temperature was increased. When tested at 450℃, the as-welded SP-700 specimen was sensitive to notch brittleness due to fast response of age-hardening at the testing temperature. The fracture appearance of the MA specimen exhibited fine dimples which increased in size remarkably with increasing temperatures. For the as-welded and W-482 specimen, the extent of intergranular fracture increased significantly with increasing temperatures. Moreover, all Ti-662 welds had a trend of increasing NTS from room temperature to 150℃, but a gradual decrease in NTS with further rises in temperature. Fatigue crack growth tests of SP700 welds were carried out at 300, and 450℃. The results were also compared with those of the MA specimen tested at the same condition. For both of the MA and welds, the identical fatigue crack growth behavior occurred at room temperature and 300℃. However, a slightly increased in crack growth rate was found at 450℃. The observation of fracture surface revealed that the MA and welds at room temperature exhibited the transgranular fatigue fracture. A pronounced rough fracture surface of the weld resulted from the inherent coarse structures of the weld, which promoted zig-zag crack path.
URI: http://ethesys.lib.ntou.edu.tw/cdrfb3/record/#G0M96550011
http://ntour.ntou.edu.tw/ir/handle/987654321/13615
Appears in Collections:[材料工程研究所] 博碩士論文

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