臺灣博碩士論文加值系統

鎳基超合金一般含有活性元素，故於澆鑄之後常氧化形成夾渣物，此時需將夾渣物加以挖除，並配合手工惰氣鎢極電弧銲加以修補，然鎳基超合金由於合金元素複雜，經銲接修補後易於銲道與熱影響區生成缺陷，主要為銲接熱裂紋；且於消除銲後殘留應力的熱處理中，於熱影響區形成裂紋，被稱為再熱裂紋。本實驗為採用惰氣鎢極電弧銲配合鎳基超合金Rene41 銲線在鎳基超合金Rene 77 上進行銲接修補，並於銲接後進行於1163℃持溫兩小時之熱處理A 或於1080℃持溫一小時之熱處理B，針對預熱溫度、基材狀況、銲接電流以及冷卻方式進行探討裂紋的生成原因，並比較其顯微結構的差異。銲補完成之試片，分別進行XRD 結晶結構分析、TEM顯微結構鑑定、金相觀察、SEM 顯微結構分析與EDS 半定量分析。
實驗結果顯示，Rene 77 與Rene 41 主要組成的相為γ基地相與γ’析出強化相，主要析出之碳化物為MC 型的TiC。在銲道內部所析出之碳化物，較為細小，主要析出於柱狀晶間，而基材的碳化物，因其於鑄造時析出故較為粗大，主要析出於樹狀晶間。當銲件經熱處理A 或熱處理B 後，基材的γ’相由立方體的邊界開始向四周成長，並有二次的γ’相以圓形析出，銲道則均勻析出圓形的γ’相。在實驗參數方面而言，基材Rene 77 經熱處理A 後，並無法將析出物有效固溶回基材之中，故基材是否經熱處理對於銲接結果並無明顯影響；就金相觀察可以發現，未預熱的試片相對於經預熱的試片而言，在銲接後將出現較大的熱影響區；選用的銲接電流越小，越不易於銲道內部形成裂紋，且減少熱輸入量將可降低銲後之殘留應力；銲後以保溫冷卻的方式冷卻可以減少急冷所造成的殘留應力的影響。但是，利用惰氣鎢極電弧銲進行銲補時，易於熱影響區中產生液化裂紋。銲補之試片經銲後熱處理後，於熱影響區有裂紋產生，此裂紋為應變時效裂紋。若於銲接後熱影響區即存在裂紋，則裂紋將沿著晶界往銲道與基材擴展。

Generally speaking, Nickel-base superalloys contained activity elements.As a result, they are found defects easily as slag entrapment in it. In this situation, we can use melt-in fusion weld to repair these defects and increase the service life of weld piece. However, the elements of nickel-base superalloys are complex, and those elements are harmful during welding. For this reason, it might cause the occurrence of post-weld cracking in welding
bead and heat-affected zone. And because of the residual stress in weldment, it would induce reheat cracking during post-weld heat treatment. The welding repair of Rene 77 Nickel alloy was performed using GTAW with Rene 41 welding wire in this investigation. After welding, two heat treatments were employed in this investigation. Heat treatment A was heated to 1163℃ and holding for 2 hrs, and heat treatment B was heated to 1080℃ and holding for 1
hr. The purpose of this study is to discuss the formation of cracking for preheating temperature, condition of base metal, welding current and cooling method. The weldments of welding repair were tested using X-ray diffraction, TEM, OM, SEM, and EDS analysis.
Experimental results indicated that the primary phase in Rene 77 and Rene 41 is γ and γ’ phase, respectively and the major precipitate carbide is TiC. The carbides in welding bead were small, and they precipitated at the grain
boundary of columnar structure. Because the carbides in base metal precipitated in casting, they were bigger than the carbides in welding bead. And they precipitated in the grain boundary of dendritic structures.
After heat treatment A or B, the γ’ phase in base metal would transfer from cube to surrounding the octodendrite, and the secondary γ’ phase would precipitate as sphere. In welding bead, γ’ phase would precipitate as sphere. Regarding to experimental parameters, the precipitates could not dissolve to base metal after heat treatment A, so the pretreatment of base metal indicated
a slight influence after welding. It exhibited a wider heat-affected zone for without preheating of specimens than with preheated samples. As the welding current was smaller, it would less susceptible to crack in welding bead. And the decrease of heat input could reduce the residual stress in welding. After welding, the slow cooling rate can decrease the residual stress which occurred in rapid cooling. However, it would cause liquation cracking in heat- affected zone using GTAW repair. After post-weld heat treated, it would lead to crack in heat-affected zone. This kind of cracking called as strain-age cracking. If the cracks exist in heat-affected zone after welding and they will propagate
from heat-affected zone to welding bead and base metal along grain boundaries.

中文摘要................................................. i
英文摘要................................................ ii
目次.................................................... iv
表目錄.................................................. vi
圖目錄................................................. vii

第一章 前言.............................................. 1

第二章 文獻回顧.......................................... 4
2-1 鎳基超合金........................................... 4
2-1-1 鎳基超合金Rene77................................. 12
2-1-2 鎳基超合金Rene41................................. 17
2-2 銲接熱裂紋.......................................... 19
2-2-1 凝固裂紋......................................... 22
2-2-2 液化裂紋......................................... 26
2-2-3 再熱裂紋......................................... 30

第三章 實驗方法......................................... 34
3-1 實驗流程............................................ 34
3-2 實驗材料............................................ 35
3-2-1 鎳基超合金Rene 77................................ 35
3-2-2 鎳基超合金實心銲線Rene 41 ....................... 36
3-3 實驗參數............................................ 37
3-3-1 銲接參數......................................... 37
3-3-2 熱處理參數....................................... 37
3-4 試片前處理.......................................... 40
3-5 SEM 顯微組織分析.................................... 40
3-6 XRD 結晶構造分析.................................... 40
3-7 TEM 相鑑定.......................................... 40

第四章 結果與討論....................................... 41
4-1 銲補參數之選擇與分析................................ 41
4-1-1 銲補參數之選擇對於裂縫之影響..................... 41
4-1-2 金相觀察分析..................................... 45
4-2 顯微組織觀察分析.................................... 46
4-2-1 XRD 結晶結構分析................................. 46
4-2-2 TEM 觀察......................................... 47
4-2-3 SEM 觀察......................................... 51
4-2-3-1 母材之SEM 觀察................................ 51
4-2-3-2 銲補區之之SEM 觀察............................ 58
4-3 銲補之缺陷成因分析.............. ................... 65
4-3-1 銲接後........................................... 65
4-3-1-1 銲道裂紋...................................... 65
4-3-1-2 熱影響區裂紋.................................. 70
4-3-2 熱處理後......................................... 76
4-3-2-1 再熱裂紋...................................... 76

第五章 結論............................................. 80

第六章 參考文獻......................................... 81

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