TEM observation of the heat-affected zone in electron beam welded superalloy Inconel 713C

The paper presents results of microstructural observations and phase analysis of electron-beam-weldedfusion zones in superalloy Inconel 713C using transmission electron microscopy. In the fusion zone, a 90% fraction of fine-grained gamma ' precipitates was found, with sizes up to 30 nm. No dislocations were observed in the precipitates or at the gamma-gamma ' interface. Primary, undissolved inclusions of gamma ' were found in the heat-affected zone (HAZ). In the HAZ, a very high concentration of dislocations was found at the gamma-gamma ' boundaries, as well as inside the gamma ' particles and in the gamma solid solution. The increased dislocation density indicates loss of coherence of that phase and the creation of a semi-coherent boundary, and is related to dissolution of the particles and intensified diffusion through the interphase gamma-gamma ' boundary. The lattice misfit coefficient Delta a/a between the gamma ' particles and gamma solution in the HAZ indicates negative values from -0.20% to -0.06%. The presence of semi-coherent boundaries and the negative lattice misfit coefficient leads to dislocation locking and can result in cracking in the HAZ. (C) 2007 Elsevier Inc. All rights reserved.