臺灣博碩士論文加值系統

本研究以雷射表面處理(Laser Surface Treatment, LST)對用於核電廠覆銲融填的鎳基合金Alloy 52進行表面修整。研究利用熱處理模擬不當銲接或長時間使用後，材料晶界劣化造成抗腐蝕能力下降，再以不同能量密度的雷射光束對覆銲層進行雷射表面重熔(Melting)處理。觀察雷射處理前後金相組織變化，並以高速鑽孔法量測表面殘留應力，抗腐蝕能力測試則採用改良惠式試驗法(Modified Huey Test)及雙環動電位再活化法(Double Loop-Electrochemical Potential-kinetics Reactivation, DL-EPR)，藉以評估其耐蝕能力提升程度。
實驗結果顯示，當試件劣化時，晶界將生成富Cr碳化物，枝晶間則有Ti析出物與細微Cr碳化物顆粒偏析，造成整體抗腐蝕能力下降。雷射重熔則將析出物重熔回基地，重熔區內組成為緻密枝晶結構，大幅提升抗腐蝕能力，熱影響區內則因析出物未完全熔融而仍有輕微孔蝕情形。然經由雷射表面重熔後將引入額外殘留張應力，其中較高能量密度之殘留張應力最高達到238.79MPa，仍小於材料降伏應力。電化學腐蝕試驗中顯示，在經過雷射重熔後敏化值(Ir/Ia)明顯降低，整體抗腐蝕能力皆優於原始銲件，故雷射表面重熔為此材料有效恢復及提升抗腐蝕能力之方式。

Laser Surface Treatment (LST) is used to repair the surface of overlaid nickel based metal Alloy 52 in this study. In simulating of welding decay by aging heat treatment, chromium carbide had precipitated in grain boundary, caused the decrease of corrosion resistance. Laser Surface Melting (LSM) is now considered to be a solution of grain boundary segregation. In addition to the investigation of metallurgic, Modified Huey Test and DL-EPR were applied to evaluate the improvement of corrosion resistance. Surface Residual Stress was examined by High-Speed Hole-Drilling strain gauge method.
In comparison with As-Welding (AW), the tensile residual stress had decreased after 650℃ aging heat treatment. LSM had increased the surface tensile residual stress that the highest tensile residual stress reached to 238.79MPa, but still lower than its own yielding stress. Metallurgic showed that chromium and titanium carbide were resolved and redistributed in melting zone, which made the intergranular and interdendritic corrosion markedly improved. However, the un-melted carbide in the heat effect zone lowered the corrosion resistance and pitting was discovered. The DL-EPR results revealed that the sensitization value (DOS, Ir/Ia) which was elevated after aging heat treatment had reduced by LSM, indicated the higher corrosion resistance. Laser surface treatment was proven to be an effective technique for the welding decay of Alloy 52 weldment surface.

摘要 I
Abstract II
目錄 IV
圖目錄 VI
表目錄 XI
第一章 前言與文獻回顧 1
1.1前言 1
1.2文獻回顧 5
第二章 相關理論 9
2.1銲道凝固理論 9
2.2雷射製程 12
2.3沿晶應力腐蝕理論 15
2.4 銲接殘留應力 17
2.5 應變規鑽孔法量測殘留應力 20
2.6 動電位再活化法原理 27
第三章 研究方法與實驗流程 30
3.1銲材 32
3.2 GTAW覆銲及銲後熱處理 33
3.3 雷射表面處理(LST)製程 35
3.4金相及微結構觀察 37
3.5 Modified Huey test抗腐蝕測試 39
3.6 雙環動電位再活化測試法 40
3.7 高速鑽孔法量測殘留應力 42
第四章 結果與討論 44
4.1覆銲組織觀察 44
4.2 熱處理後組織觀察 47
4.3 雷射表面處理形貌觀察 54
4.4雷射表面處理殘留應力 58
4.5 Modified Huey Test測試結果 64
4.6 DL-EPR測試結果 70
第五章 結論 77
第六章 參考文獻 78

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