Laves Phase in Alloy 718 Fusion Zone

Abstract

The gas tungsten arc (GTA) welded fusion zone of alloy 718 has been well investigated on the formation of interdendritic Laves phase. This article deals with the various process control methodologies for minimizing the microsegregation and Laves phase such as the enhanced weld cooling rate in GTA welding (GTAW) process and modification in weld metal chemistry. Even though the high energy density welding processes such as electron beam (EB) and laser beam (LB) welding techniques are proven in minimizing the microsegregation and Laves phase, the requirement of conventional GTA welding process still exists in the aerospace industry due to the complex shapes of the components and the inaccessible conditions for executing the welding process. The enhance- ment in the weld cooling rate and modified weld metal chemistry resulted in the refined fusion zone microstructure and reduced microsegregation. Enhanced weld efficiency on ultimate tensile strength (UTS) and 0.2% YS at 25°C was observed to the tune of 85 to 93% by employing cryogenic cooling in GTA welding process. Similar improvement in weld efficiency at 650°C was observed. However, the evaluated weld efficiencies with cryogenically cooled weld metal were marginally lower than the previous works in EB and LB welds only by 2–3%.