Metallurgical modeling of intergranular HAZ liquation cracking during laser welding newly developed crystallography-dependent aerospace materials. Part I: Spontaneous microcrack repair of microstructure development

Abstract

Metallurgical modeling of microcrack self-repair during laser welding of nickelbased superalloys has been properly established. Metallurgical mechanism of crystallographic control self-repair intergranular liquation cracking of heat-affected zone (HAZ) through spontaneous feed of interdendrite liquid beneath the surface is proposed. Self-repair of arterial crack network with dendrite substructure of backfill enables crack resistance amelioration and is dependent on alloying element and heat input. Microstructure development and solidification behavior are controlled to minimize the severe liquation cracking near the fusion boundary by optimization of laser welding conditions through numerical analysis. Liquid healing of incipient cracking in the HAZ through available feeding fluid flow due to accessible to weld pool are sensitive to grain size and weld pool geometry to metallurgically suppress liquation crack, stabilize the primary solidification path and improve the weld integrity, simultaneously. It is revealed that optimum low heat input is favored to reduce liquation cracking. Theoretical predictions are in satisfactory agreement with microanalysis of measurement result indirectly. In addition, this metallurgical modeling is also applicable to other nickel-based superalloys with similar metallurgical properties.