雷射表面處理修補衰化之Alloy 82覆銲層效果研究

Rejuvenation of Weld Decayed Alloy 82 by Laser Surface Treatment

本研究採雷射表面處理（Laser surface treatment, LST），對衰化之Alloy 82覆銲層進行重熔修復，探討其耐蝕能力恢復機構，藉惠氏腐蝕測試法觀察修復範圍，並透過雙環動電位再活化法量化修復效果。實驗結果顯示，LST試件之重熔區及熱影響區未發現枝晶間孔蝕。原因為雷射掃描過程中，重熔區鉻、鈮析出物重新熔回鎳基地，消除局部缺鉻而恢復耐蝕性能。熱影響區雖未熔融，但由微觀結構可見其枝晶間富鈮組織在高溫熱歷程中亦固溶回枝晶內部。此外原基地中碳化鈦、碳化鈮等具強化作用之顆粒狀析出物在熱影響區中仍存在，故熱影響區在機械性能上應優於重熔區。在電化學腐蝕測試中，雷射處理試件之重熔、熱影響區皆測得較衰化試件低之敏化值（Ir/Ia），由此確認LST能夠有效修補衰化Alloy 82覆銲層。

Laser surface treatments were studied for their feasibility in repairing the decayed Alloy 82 weldment where the weld decayed zone is rejuvenated and corrosion resistance is recovered. Modified Huey test was employed to reveal the width of rejuvenated area, and double loop-EPR test was employed to evaluate the corrosion resistance of each specimen. The experimental results showed that interdendritic pitting resistance of laser treated specimens was remarkably improved both in melted zone and heat affected zone where Nb-rich phases were resolved. However, TiC/NbC or (Nb,Ti)C particles remained unresolved in the heat affected zone. As a consequence, heat affected zone had a superior mechanical strength than melted zone. The DL-EPR results revealed that laser treated areas with lower reactivation current and degree of sensitization values (DOS, Ir/Ia) indicated higher corrosion resistance. Hence, laser surface treatment is proven to be a practical technique for repairing the decayed Alloy 82 weldment.