Single pass carbon dioxide laser joining of indium 718 superalloy with filler

Laser beam welding is an attractive joining technique for fabrication and repair of service damaged aerospace gas turbine engine components made from nickel-based superalloys. A major factor that, however, limits the weldability of superalloys is the formation of cracking both during welding and post weld heat treatment. Previous studies have shown that weld cracking in superalloys can be significantly influenced by welding parameters and material pre-weld heat treatment. In the present work, CO2 laser beam welding, with the use of filler wire, one of the most widely used nickel based superalloy, IN 718, subjected to different pre-weld heat treatments was studied. The use of filler alloy during welding resulted in a crack-free fusion zone but grain boundary liquation cracking occurred in the heat affected zone (HAZ). The cracking was observed to increase with increased laser beam power and welding speed, and by post weld heat treatment. A pre-weld heat treatment was found in the study to be beneficial in preventing the HAZ cracking both during welding and post weld heat treatment. The effectiveness of the pre-weld heat-treatment is attributable to a combined effect of minimized grain boundary segregation of melting point depressant element, boron, and inhibition of thermally induced grain growth.