Defects characterization of welded specimens by transmission electron microscopy

Austenitic Type 304L stainless steel (SS) and martensitic Alloy EP-823 have been identified as candidate structural materials to contain spallation target for transmutation of nuclear waste. Welded specimens consisting of either or both materials have been evaluated by transmission electron microscopy (TEM) to determine the dislocation density near the heat-affected-zone (HAZ) and the base material. The results indicate that the average dislocation density determined from the TEM micrographs taken at different locations was much higher near HAZ compared to that of the base material. Further, the estimated dislocation density was higher on the Alloy EP-823 side of the weld than that of the Type 304L SS side possibly due to the faster rate of solidification of the martensitic alloy. Higher dislocation density is an indication of enhanced residual stress resulting from the welding operation.