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-welded fusion zones in superalloy Inconel 713C using transmission electron microscopy. In the fusion zone, a 90% fraction of fine-grained γ′ precipitates was found, with sizes up to 30 nm. No dislocations were observed in the precipitates or at the γ–γ′ interface. Primary, undissolved inclusions of γ′ were found in the heat-affected zone (HAZ). In the HAZ, a very high concentration of dislocations was found at the γ–γ′ boundaries, as well as inside the γ′ particles and in the γ 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 γ–γ′ boundary. The lattice misfit coefficient Δa/a between the γ′ particles and γ 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.