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Please use this identifier to cite or link to this item: http://ntour.ntou.edu.tw:8080/ir/handle/987654321/42737

Title: Ti-15V-3Cr-3Al-3Sn合金於熱氫製程下之顯微結構演變與機械性質變化研究
Authors: CHANG, YUNG-JU
張詠茹
Contributors: NTOU:Institute of Materials Engineering
國立臺灣海洋大學:材料工程研究所
Keywords: Ti-15V-3Cr-3Al-3Sn;液態熱氫製程;晶粒細化
Ti-15V-3Cr-3Al-3Sn;liquid thermohydrogen process;grain refinement
Date: 2016
Issue Date: 2017-05-24T08:17:43Z
Abstract: 本論文研究主要針對Ti-15V-3Cr-3Al-3Sn合金(簡稱Ti-15-3)先經液態熱氫製程(thermohydrogen process,簡稱THP)處理之後,研究合金顯微組織在液態熱氫製程各階段的變化演進,並探討其與機械性質變化之關係。另外,為了進一步細化晶粒以及提升對機械性質的影響,而嘗試在熱氫製程前先進行滾軋,藉由結合熱機與熱氫製程的方式,探究細化晶粒之程度與合金之機械性質變化。結果發現Ti-15-3合金於液態滲氫階段(分別滲氫5、10、15、20、25及30小時),在電解充氫時間超過10小時後,過程中因足量的氫原子滲入合金內而擠壓晶格,內應力誘使β相晶粒內會產生ω過渡相之滯熱相轉換(athermal transformation)。液態電解滲氫20小時後,此相轉換之特徵更形明顯,由於氫原子進至β相内充當間隙原子,形成β相溶有過飽和氫原子(βH),並誘發產生相(β+H2→βH+),導致β晶粒內有類似雙晶平行晶界特徵之金相顯微形貌。經由TEM分析,ω相於β相次晶粒內與β相形成交替層狀結構,而且存有(111)β//(0001)ω之方位關係。 Ti-15-3合金液態熱氫製程,在電流5 mA,滲氫20小時後,經760C,5小時氫化處理,最後經780C,1.5小時後,由於晶粒細化以及細長α相於β相晶粒內交錯分布,使其有最佳表面硬度及拉伸強度。此外,Ti-15-3合金以冷加工百分率50%結合熱氫製程之機械性質,由於再結晶使晶粒細化,合金的表面硬度值為307 Hv、抗拉強度為812 MPa。其微觀破斷面中明顯的出現頸縮現象以及韌窩狀組織,這些均為典型塑性破斷特徵。結果,合金材料呈現具高硬度、較佳的拉身強度與延展性。
The research mainly aims to study the microstructural evolution of Ti-15V-3Cr-3Al-3Sn(so-call Ti-15-3) during a liquid thermohydrogen process (so-called THP) as well as the dependence of microstructure and mechanical properties. Besides, in order to further refine grain and enhance the effect on the mechanical properties, cold work rolling before being liquid thermohydrogen processed was also triedout.The effect of combination of thermomechanical plus THP on the degree of grain refinement and the variant of mechanical properties were discussed as well. As Ti-15-3 alloy was carried out liquid THP separately at various hydrogen-charging time (5, 10, 15, 20, 25 and 30 h), the results show that an athermal transformation of ω transitionappeared near the hydrogen-charging surface Ti-15-3 alloy after electrolysis hydrogen-charging was executed over 10 h, in which plenty of hydrogen atoms diffused into the lattice of β phase and then distorted the lattice leading to the stress-inducedωtransition. Following 20 h of electrolysis hydrogen-charging, the feature of the transformation showed much apparently.Because a great deal of hydrogen atoms diffused into the lattice and served as the interstitials, the β phase (βH) dissolving plenty of hydrogen atomsformed and resulted in the stress-induced ω transition (β+H2→βH+). Consequently, the metallography shows the twin-like features, where the parallel subgrain boundaries appeared in the β grains. From TEM analysis, ω phase existed in the subgrain of β phase and formed the alternating layer structure with β phase.Furthermore, there is an orientation relation of (111)β//(0001)ω in the subgrain. The liquid THP of T-15-3 alloy carried out 20 h electrolysis hydrogen-charging with 5 mA current, followed by 760C hydrogenation treatment for 5 h and then dehydrogenation at 780C for 1.5 h can attain the excellent surface hardness and tensile strength due to the back-weave-like morphology and the grain refinement after the liquid THP. In addition, as forthe Ti-15-3 alloy carried out cold work rolling before being liquid THP, it displayed the surface hardness of 307 Hv and the ultimate tensile strength of 812 MPa due to the grain refinement of recrystallization resulting from the combination effect of thermomechanical process and THP. The macro- and micro-scopic fractographs apparently show the necking and the dimple morphology, which are the distinctive feature of plastic fracture. The processed Ti-15-3 alloyconsequently exhibited high hardness, good ultimate tensile strength and ductility.
URI: http://ethesys.lib.ntou.edu.tw/cgi-bin/gs32/gsweb.cgi?o=dstdcdr&s=G0010355017.id
http://ntour.ntou.edu.tw:8080/ir/handle/987654321/42737
Appears in Collections:[材料工程研究所] 博碩士論文

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