Role of filler alloy composition on laser arc hybrid weldability of nickel-base IN738 superalloy

Laser arc hybrid weldability study was performed on nickel-base IN738 superalloy using nickel-base filler alloys of various compositions. Propensity for heat affected zone (HAZ) intergranular liquation cracking in the weldments was observed to vary depending on the Al+Ti+Nb+Ta concentration of the weld metals produced by the different filler alloys. Detailed study, including SEM and TEM analyses, thermodynamic calculations and microhardness evaluation revealed that variation in HAZ cracking susceptibility of IN738 superalloy when different filler alloys are used during laser arc hybrid welding can be attributed to variation in the extent of precipitation hardening produced in the weld metals. Additionally, shrinkage, and the consequent volumetric changes, due to γ′ precipitation in the weld metals could have contributed to excessive tensile loading of the crack susceptible HAZ and aided intergranular liquation cracking.