Effect of Nd:YAG laser welding on microstructure and mechanical properties of Incoloy alloy 800

Abstract

Incoloy alloy 800 is a superalloy particularly suited to aggressive corrosive environments. Both weld quality and productivity may be enhanced when joining parts by laser beam welding (LBW). The current paper describes joining of Incoloy alloy 800 plates (4 mm thickness) by laser welding (Nd:YAG). The laser scan speed was varied between 0.5 and 2 m/min for a constant power input (laser). The evolution of the microstructure was investigated utilizing both traditional and advanced microscopic techniques. The results indicated an hourglass shaped fusion zone which was slightly larger on the top surface. Elongated columnar but fine equiaxed dendrites were present in the fusion zone. Significant phase transformation occurred because of a higher cooling rate that is typical with laser welding. An uneven and planar distribution of dislocations associated with subgrain boundaries were observed adjacent to Laves phases. The formation of Laves phases at the lowest scanning speeds reduced the mechanical properties. Mechanical testing showed that the joints failed in the weld zone at the lower scanning speeds because of the presence of the Laves phases. Ductile fracture was demonstrated at the higher scanning speeds whereas brittle fracture occurred at the lower scanning speeds.