Nano-size solidification microconstituents in electro-spark deposited Ni-base superalloy

The microstructure of electro-spark deposited IN 718 was investigated by analytical transmission electron microscopy. The analysis shows in contrast to general assumption, extreme rapid cooling rates involved in electro-spark deposition (ESD) did not produce partitionless solidification, devoid of second phase microconstituents in the material. Nanosized Laves and MC carbide particles were formed in the interdendritic regions of IN 718 electro-spark weld deposit, which indicate the occurrence of segregation-induced phase formation during solidification of the weld. The formation of Laves phase particles, which is known to be deleterious to the mechanical properties of IN 718, requires adequate consideration in the application of IN 718, and possibly other Nb-bearing nickel-base superalloys, processed by ESD.