Microstructural investigations of electron beam welded alloy 718

Abstract

Electron beam welding is used to join components where welding distortions have to be minimized and good weld integrity is a must. This paper reports the results of microstructural investigations carried out on Alloy 718 welded in the aged condition. A region of width 200 μm at a distance of 500 μm from the fusion zone interface in the heat affected zone (HAZ) showed extensive deformation bands. Micro-hardness measurements showed softening in the HAZ region close to the fusion zone interface and hardness values the same as that of region far away from the weld zone in the rest of the areas including the deformed region. The influence of post weld heat treatments on integrity of weld was carried out. Profuse faulting and twinning and planar arrangement of dislocations were observed in the deformed region and in the areas close to fusion interface in the HAZ, dissolution of γ″ particles has occurred. The present observations are rationalized in terms of the temperature seen in the HAZ zone and also the residual strain generated due to heating and microstructural changes during welding.