Investigation of Dendritic Growth and Liquation Cracking in Laser Melting Deposited Inconel 718 at Different Laser Input Angles

Nickel-baresulting in the higher sed Inconel 718 (IN718) superalloy is deposited on a polycrystalline substrate by laser melting deposition. The effects of the laser input angle on the dendritic microstructure, crystal orientation and heat-affected zone (HAZ) liquation cracking tendency are studied by optical microscopy, scanning electron microscopy, and electron backscatter diffraction. Larger laser input angles improve the lateral temperature gradient, enhance growth of secondary dendrites, and establish firm interconnections among secondary dendrites in the interdendritic regions, resulting in the formation of a “cross-band” morphology inside the grains, especially laser input angles of 10° and 20°. Larger laser input angles also improve the homogeneity of heat dissipation flow during solidification in laser deposition as well as the resulting in the higher crystal orientation. The enhanced interdendritic bonding improves the cracking resistance of the crystal inner grain and attributed to the decrease in the grain boundary misorientation, the stability of liquation film at the grain boundaries reduces. Owing to these two reasons, the susceptibility to HAZ liquation cracking is effectively depressed when using larger laser input angles in laser deposition.