Nanoscale carbide precipitation in the recast layer of a percussion laser-drilled superalloy

The microstructure of the recast layer formed during percussion laser drilling of a powder-metallurgy Ni-based superalloy has been studied using electron microscopy in conjunction with focused ion beam serial section tomography. It is shown that the dendritic microsegregation of Ti in the supersaturated gamma recast grains reported previously is accompanied by the formation of nanoscale precipitates in the regions between the dendrite arms. Transmission electron microscopy analysis of extraction replicas has shown that the precipitates are Ti-rich MC-type carbides.