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Please use this identifier to cite or link to this item: http://ntour.ntou.edu.tw:8080/ir/handle/987654321/9556

Title: Ti-15-3合金應用研究---Ti-15-3合金板材及銲件機械及疲勞裂縫成長特性研究
Mechanical and Fatigue Crack Growth Behaviors of Ti-15-3 Alloys and Welds
Authors: 蔡履文
Contributors: NTOU:Institute of Materials Engineering
國立臺灣海洋大學:材料工程研究所
Date: 2009-08
Issue Date: 2011-06-28T07:09:31Z
Publisher: 行政院國家科學委員會
Abstract: 摘要:鈦合金基本上分為α、nearα、α-β及β四大類,其中α-β及β型 鈦合金可經由熱處理來改變其顯微組織,因而其機械性能隨著產生變化, 而β型鈦合金由於其穩定之結構,且經未時效處理前有良好之成型性,而 時效後其強度則可大幅提升,因此β型鈦合金之用量呈現快速成長,其中 以Ti-15V-3Cr-3Al-3Sn 為典型代表合金。但一般β 型鈦合金添加大量合 金元素,因此銲接性較其他鈦合金差。本多年期研究為針對Ti-15-3 合金, 評估板材及銲件經不同時效處理後,其機械及疲勞裂縫成長特性,探討不 同顯微組織對阻擋裂縫成長之效益。 第一年 將原始板材,使用二氧化碳雷射,進行不加填料雷射銲接,將銲後銲 件及板材施行不同條件之時效處理,實驗進行試件硬度量測、拉伸試驗及 觀察各試件之顯微組織,並將板材及銲件獲致之結果相互比較。不同時效 之板材及銲件,在大氣環境中,於不同應力比條件下,進行疲勞裂縫成長 試驗,實驗各不同試件以穿透式電子顯微鏡觀察細微組織,掃描式電子顯 微鏡觀察各不同試件之破壞特微。 第二年 從以往觀念均認為鈦合金極易生成鈦-氫化物而產生脆化,但最近研究 結果顯示,α-β型鈦合金,包括SP-700 或Ti-6-4,在氣態氫環境中,並未 產生明顯氫致疲勞裂縫成長加速現象,在相同測試條件下,發現304 不銹 鋼或高強度鋼均有十分顯著之氫加速裂縫成長情形。廣泛蒐集以往發現之 文獻,發現無論使用動態疲勞負載或靜態拉伸測試,被測物鈦合金均是已 經具備相同高濃度之氫含量,某些試件其氫含量高達5000 ppm。β型鈦合 金對氫有很高固溶度,高固溶度亦伴隨低氣態氫脆性,本研究為延續先前 研究成果,探討Ti-15-3 鈦合金在氣態氫環境下,評估不同時效板材或銲 件,其疲勞裂縫成長特性,同時依據吳教授氫滲試驗結果,瞭解氫擴散特 性對不同形式鈦合金之影響。 第三年 本年度研究是利用本研究群體先前研究成果,子計畫吳台一教授以先 行充氫再脫氫方式,來達成鈦合金晶粒細化之目的,利用此計劃的發展之 技術,來細化鈦合金雷射銲道組織,進而評估這些細化組織之缺口強度及 疲勞裂縫成長特性,並與粗大銲道特性進行比較。本年度研究有助於此研 究群體之橫向研究整合及設備整合。
abstract:Titanium alloys can be mainly divided into four groups, i.e., α, near α, α-β, and βtitanium alloys. In case of α-βand βalloys, the microstructures can be altered through heat treatment hence the mechanical properties will behave great changes depending on the inherent microstructures. The high forming ability together with high strength after aging treatment make βtitanium alloys increase its applications in different industries. The typical βtitanium alloy can be Ti-15V-3Cr-3Al-3Sn (Ti-15-3). The demand of this alloy in certain aircraft is even over Ti-6Al-4V, one of the most widely used α-βtitanium alloys. However, the high alloy contents of βtitanium alloy are found to deteriorate its inherent weldability. In this work, the fatigue crack growth behaviors of Ti-15-3 alloy plate and welds, with and without postweld heat treatment or ageing treatment, will be evaluated, especially pay attention to the effects of aging conditions on the mechanical properties of the specimens. The detail microstructures of various specimens will be examined by transmission electron microscope (TEM). Moreover, the variation in fatigue crack growth behaviors will be correlated with the microstructures in distinct specimens. The first year of the project will focus on the influence of aging conditions on the tensile and fatigue crack growth properties of the alloy plate and welds. The effect of stress ratio on the enhanced crack growth rate of the postweld-heat-treated welds will be determined and compared with the counterpart base metal. Hydrogen has been regarded as a candidate to replace fossil fuel. However, most of the structural materials are found to be sensitive to hydrogen embrittlement. The βtitanium alloys are reported to be more tolerate and have high hydrogen solubility. It may make this alloy resistant to gaseous hydrogen embrittlement. The second year of the project will pay attention to the effect of hydrogen on the enhanced crack growth rate of the Ti-15-3 alloy and welds. The test will cope with the work of hydrogen permeability performed by professor Wu. Microstructural effects on the hydrogen permeasion will be related with hydrogen-accelerated crack growth. Coarse structures are known to damage the mechanical properties of Ti-15-3 alloy in comparison with the fine grained one. In the third year of the investigation, a special hydrogen-charging procedure developed by Professor Wu will be used to refine the coarse microstructure of the welds. The influence of coarse solidified microstructures on the fatigue crack growth rate of various specimens will be compared with the counterpart specimens with fine grained size. Fatigue fracture appearance of various specimens were examined by scanning electron microscopy (SEM) to identify typical fracture features and correlated with fatigue crack growth characteristics.
Relation: NSC98-2221-E019-008
URI: http://ntour.ntou.edu.tw/ir/handle/987654321/9556
Appears in Collections:[材料工程研究所] 研究計畫

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