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题名: Ti-6Al-4V合金之氣態充氫晶粒細化製程研究
Grain Refinement of Ti-6Al-4V Alloy by Gas Phase Hydrogenation
作者: J. P. Wu
吳榮賓
贡献者: NTOU:Institute of Materials Engineering
國立臺灣海洋大學:材料工程研究所
关键词: Ti-6Al-4V
日期: 2006
上传时间: 2011-06-30T07:23:11Z
摘要: 以往傳統觀念認為氫在一般材料中被視為一種有害的元素,現在已可經由在氫環境中利用不同熱處理而改善並提升鈦合金機械性質,主要是利用鈦與鈦合金對氫元素之間具有很高的親和力,而氫在鈦合金中主要是以形成固溶氫或形成脆性氫化物的形式存在,再利用氫原子與鈦之間的可逆性,氫原子很容易在高溫高真空的除氫製程中將氫除去,因而達到晶粒細化的成效。 本研究首先利用物理氣態充氫的方式將氫固溶至鈦合金中,在不同充氫條件下其影響參數包含:溫度、氫氣分壓以及充氫時間,探討這些參數對於充氫的影響性,研究結果顯示隨著充氫後氫含量的增加提供大量的氫化物分解位置因而促使鈦合金晶粒細化程度的提升,但也由於過高的氫含量導致裂縫的生成並且不利於往後共析分解反應的進行,因此氫含量控制在1 wt%左右可獲得最佳細化效果。再來針對Froes等人在1990年研究開發的熱化學氣態充氫製程TCT(thermochemical treatment)以及近幾年所開發的熱氫製程THP(thermohydrogen processing),加以探討其顯微組織的變化情形以及比較晶粒細化後機械性質的提升差異性。研究結果顯示,TCT熱化學氣態充氫製程主要以細化α相為主,其細化後仍就維持著層狀組織;THP熱氫製程則主要以細化β相為主,所得到的細化組織類似等軸α相晶粒的結構。就機械性質來看以THP熱氫製程細化後硬度值較TCT熱化學製程細化後所得到之硬度值高。最後利用THP熱氫製程進行循環細化,用以探討不同次數循環下其顯微結構的細化程度,研究結果顯示循環次數的增加有助於晶粒細化後機械性質的提升,但也由於過多裂縫的生成因而無法進行多次循環。
Hydrogen was regarded as a harmful element for some general metallic materials in traditional concepts, but it can enhance the mechanical properties of titanium alloys through different thermochemical procedures . By the presence of hydrogen, hydrogen diffuses into titanium to form solid solution or hydride. Titanium and titanium alloys have large affinity for hydrogen and dissoluted hydrogen can be easily to removed by vacuum annealing. The dissolving and removing processes of hydrogen in titanium alloy is reversible, as a results grain refinement of their alloys. In this study, that hydrogenation in several effective parameters has been discussed, including: temperature, hydrogen pressure and hydrogenation time, by gas phase hydrogenation. The results indicates that it can supply large hydride dissolution site increasing with hydrogen concentration after hydrogenation, as a results enhance the efficiently of grain refinement, it has the best efficiency under the hydrogen concentration about 1 wt%. TCT(thermochemical treatment) was developrd by Froes in 1990s and then renamed and modified as THP(thermohydrogen processing). It can be evaluated through the microstructure variation and enhance the mechanical processability of titanium alloys by grain refinement. The results indicates it mainly refine the α phase and its microstructure still maintain Widmanstatten structure after TCT procedure;the THP procedure can refine the β phase and its microstructure likes equi-axed α phase. For mechanical property, the hardness of THP procedure is higher than TCT procedure. Finally, we developed a cyclic thermohydrogen processing(CTHP) to refine the microstructure by different cycles of hydrogenation -dehydrogenation and significant improvement on mechanical properties of titanium alloys have been obtained. The results indicates it can enhance its mechanical property after a cyclic thermohydrogen processing increase with cycle times, but it can not have many cycles owing to many cracks.
URI: http://ethesys.lib.ntou.edu.tw/cdrfb3/record/#G0M94550011
http://ntour.ntou.edu.tw/ir/handle/987654321/13571
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