摘 要
高鋁鈦含量的Inconel 738LC為一不易銲補，但廣泛應用在能源、國防等領域的鎳基超合金，本研究嘗試利用Inconel 738LC合金粉末進行雷射熔融沉積，藉由調整雷射功掃描速率，觀察不同製程參數下的顯微組織形成機制，透過製程的優化與基板的選擇改善沉積層與基板間的裂縫的產生與其延伸。由金相組織觀察顯示，裂紋容易發生在高角度晶界上，後續再穿晶延伸，並且在裂縫邊緣可以觀察到碳含量的富集，顯示裂紋是碳化物和熱應力共同引發的液化裂紋；隨著雷射功率與能量密度的提高，其晶粒以柱狀晶為主，沉積層與基板間的裂縫也跟著增加。而降低雷射功率則可以觀察到裂紋逐步消失，但取而代之的是由於能量密度不足導致粉末未熔融，產生孔洞或氣體捲入產生之氣孔，其晶粒則以等軸晶為主。本研究優化了熔融之參數與顯微組織，決定出Inconel 738LC合金的理想製程空間，可望應用到耐高溫、具複雜形狀的Inconel 738超合金零組件上，如渦輪葉片銲補之場域當中。關鍵詞：雷射金屬沉積、Inconel 738LC、液化裂紋、銲補
ABSTRACT
Inconel 738LC is widely used in energy, defense, and other applications. It is a nickel-based superalloy containing high aluminum and titanium concentration which makes it difficult to weld. The current study attempts to use Inconel 738LC alloy powder for Laser Metal Deposition (LMD) by adjusting laser power and scan speed. Microstructures and macro-defects were observed with different process parameters. By optimizing LMD process parameters, the formation of cracks and pores can be reduced. Metallographic structures show that cracks tend to initiates with carbon enrichment and extend along high-angle grain boundaries, forming liquation cracks due to local carbide formation and thermal stress. With the increase of laser power and energy density, the grains are mainly columnar grains, and the cracks are present to initiate from the interface of weldment and base metal. By reducing the laser power and scan speed, number of cracks decreased, however lack of fusion and pores are observed in the structures due to insufficient energy density. The weldments are dominated with equiaxed crystals. In this study, the LMD parameters and microstructure were optimized, and the ideal process window of Inconel 738LC alloy was determined. The LMD processes is shown applicable for repairing high-temperature components, such as turbine blades.Keywords: Laser Metal Deposition, Inconel 738LC, Liquation Crack, Welding Repair