臺灣博碩士論文加值系統

Inconel 718鎳基超合金擁具有良好之高溫強度、耐高溫腐蝕等優異性質，同時亦具備優良之鑄造性、加工性及銲接性。然在使用結構體組裝完成後，原材會經過反覆熱處理，而銲道會經過鏟修、反覆銲接與熱處理等製程。本研究主要在反覆熱處理對Inconel 718機械性質之研究基礎上，針對其機械性質擁有特殊變化之試片，進行微觀結構觀察，探討固溶時效反覆熱處理對微觀組織與機械性質之影響。
實驗結果顯示，M4{2次（980℃*1h/980℃*1h/720℃*8h/620℃*10h）}顯微組織在晶界之δ相連續，且大量長入晶粒，M10{4次（980℃*1h/980℃*1h/720℃*8h /620℃*10h）}晶界δ相不連續，且無長入晶粒，應是受反覆熱處理影響，M10δ相到達溶解臨界點，不再和M4相同隨反覆熱處理次數增加而累積析出，轉而大量融回基地，之後M13{5次（980℃*1h/980℃*1h/720℃*8h/620℃*10h）}δ相溶解溫度恢復超過固溶溫度，δ相又累積，強度降低，回到接近M1{1次（980℃*1h /980℃*1h/720℃*8h/620℃*10h）}的拉伸強度值，顯有循環回歸之趨勢。
M11{4次（1065℃*1h/1065℃*1h/720℃*8h/620℃*10h）}在晶界上有許多顆粒狀NbC及少量NbC薄膜，M14{5次（1065℃*1h/1065℃*1h/720℃*8h/620℃*10 h）}晶界顆粒狀NbC及大量NbC薄膜並存，抵抗晶界滑移，導致M14伸長率及衝擊韌性大幅提昇，而M9{3次（1065℃*1h/1065℃*1h/760℃*10h /650℃*10 h）}顯微結構，晶界之顆粒狀NbC比M11更密集，雖較多晶界顆粒NbC能提昇延展性，但仍和M11、M14有同樣問題，較多的晶界顆粒狀NbC或大量晶界NbC薄膜於銲接時，極有可能在熱影響區增加微裂縫生成機會，不排除此為造成銲件提前破裂的原因。

The Inconel 718, a nickel-based superalloy with its high strength and high corrosion resistance at elevated temperature, becomes a popular superalloy for high high temperature application in the past decades. It has good castability, workability, and weldability enabling it being widely used to produce aero-parts and as structural material. This research is based on the mechanical properties of Inconel 718 after cyclic heat treatment. In accordance with the special changes of the testing pieces on its mechanical properties, the cyclic heat treatment has significantly affected the microstructure and the mechanical property.
The results of M4 condition {twice heat treatment （980℃*1h/980℃*1h/ 720℃ *8h/620℃*10h）} show that the δ phase precipitate significantly on both grain boundary and within the grain with the needle shape. At M10 condition {4 times heat treatment（980℃*1h/980℃*1h/720℃*8h /620℃*10h）}. δ phase does not continuiously precipitate on grain boundary and the amount of δ phase are significantly decreased in the grain interior. It suggests that at M10 condition δ phase may reach the critical point of dissolution, which differs from M4 with lots of δ phase accumulated. In other words, once the critical point of dissolution is reached, further cyclic heat trement would not produce extra precipitated δ phase may also result in the precipitates dissolve into the matrix.
At M13 condition {5 times heat treatment（980℃*1h/980℃*1h/720℃*8h /620℃*10h）} the dissolving temperature of δ phase is hogher than that operating temperature of solution treatment, δ phase may significantly precipitate, loading to its decreased of M13 to a value close to the M1 condition {1 time heat treatment（980℃*1h/980℃*1h/720℃ *8h /620℃*10h）}. Obviously, it had a similar trend of circulating.
At M11 condition {4 times heat treatment（1065℃*1h/1065℃*1h/720℃*8h /620℃*10h）}, many NbC particles and a few NbC films are found. At M14 condition {5 times heat treatment（1065℃*1 h/1065℃*1h/720℃*8h/620℃*10 h）} , it appears significantly amount of NbC particles as well as NbC films present on the grain enhancing the resistance of grain boundary sliding , therefore its ductily and toughness. At M9 condition {3 times heat treatment（1065℃*1h/ 1065℃*1h /760℃*10h/650℃*10 h）},the NbC particles are more intensity presitipated at grain boundary than that M11 condition, althougth the presence of NbC particles may enhance the ductily of Inconel 718. However,similar problem as M11 and M14 may occur when welded. The significantly amount of NbC particles and NbC films at grain boundary may possibily produce microfissuring in HAZ, which is a possible reason for unexpected earlier fracture.

誌謝 ii
摘要 iii
ABSTRACT iv
目錄 vi
表目錄 viii
圖目錄 ix
1.前言……………… 1
2.文獻回顧 2
2.1簡介 2
2.2鎳基超合金發展背景 2
2.3鎳基超合金種類、特性 3
2.4鎳基超合金Inconel 718 4
2.4.1Inconel 718發展及應用 4
2.4.2Inconel 718成分及合金元素的影響 5
2.4.3Inconel 718顯微組織及其影響 7
2.4.4Inconel 718強化機構 10
2.4.5Inconel 718熱處理 12
2.4.6Inconel 718銲接及龜裂 13
3.實驗方法與步驟 31
3.1實驗規劃 31
3.2實驗步驟 31
3.2.1實驗材料 31
3.2.2顯微組織分析 31
3.2.3耐蝕性分析（動態極化） 33
4.結果與討論 49
4.1金相顯微結構觀察 49
4.2XRD觀察分析 52
4.3SEM顯微結構觀察 53
4.4TEM顯微結構觀察 60
4.5耐蝕性測試（動態極化） 61
5.結論 91
參考文獻 93

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