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題 名 | Brittle-to-Ductile Transition Temperature and Its Controlling Mechanism in Ti-47 Al-2Mn-2Nb Alloy=Ti-47 Al-2Mn-2Nb合金之脆性與延性轉換溫度與其控制機理 |
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作 者 | 林棟樑; 王瑜; 劉俊亮; 傅崇隆; | 書刊名 | 中國工程學刊 |
卷 期 | 22:1 1999.01[民88.01] |
頁 次 | 頁55-60 |
分類號 | 440.39 |
關鍵詞 | TiAl合金; 拉力性質; 脆性與延性轉換溫度; 應變率; TiAl alloy; Tensile properties; Brittle-to-ductile transition temperature; Strain rate; |
語 文 | 英文(English) |
中文摘要 | 近薄層微結構之雙相 Ti-47 Al-2Mn-2Nb 合金以 10 �笐疆� 10�笐臃�笐謊傅亄v 在不同溫度之拉力性質評估其脆性與延性轉換( BDT )溫度( T �滿慼^。拉斷面採用掃瞄 式電子顯微鏡觀察及以穿透式電子顯微鏡研究變形次結構, 實驗中所找到之 T �滿憮�之定 義為相對於 7.5% 延伸率之溫度,當應變率由 10 �笐羹W加至 10 �笐� s �笐螳氶A T �滿� 由 1023K 增加到 1373K 以上。 T �滿撒P應變率之關係,配合 Z ener-Hollomon 係數,得 到視活化能 324KJ/mol,此值約為γ - TiAl 相之自擴散及相互擴散之活化能。 在 T �滿� 溫度之下及上之主要破斷面分別是貫晶式破裂與酒渦狀破裂。 在 T �滿撥贖蛌�近,最普及 之 1/2<110] 正常差排開始攀爬。 以上實驗結果,可採用 Nabarro 模式理論證實,並結論 此合金之 BDT 由差排攀爬主控。 |
英文摘要 | Brittle-to-ductile transition (BDT) temperature (TBD) has been evaluated according to temperature dependence of tensile properties under different strain rates from 10 �笐� to 10 �笐� s �笐� in a two-phase Ti-47AI- 2Mn-2Nb alloy with near lamellar microstructure. Tensile fractography was observed using a scanning electron microscope while deformation substructures were investigated using a transmission electron microscope. It was found that TBD. when defined as the temperature corresponding to 7.5% elongation, increases from 1023K to more than 1373K, the strain rate increases from 10 �笐� to 10 �笐� s �笐�. Based on the strain rate dependence of T□ (and using the Zener-Hollomon factor) an apparent activation energy of 324kJ/mol was obtained, which is approximate to the self- and inter-diffusion activation energies in the γ -TiAl phase. Transgranular fracture and dimple fracture were found to dominate in fracture surfaces below and above TBD. respectively. Furthermore, the most popular 1/2<l 10] ordinary dislocations were found to begin to climb around TBD. All this evidence, as well as a theoretical calculation using the Nabarro Model, add up to a conclusion that the BDT of the alloy is controlled by dislocation climbing. |
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