Interplay between solidification microsegregation and complex precipitation in a ?/?? cobalt-based superalloy elaborated by directed energy deposition

This study examines the segregations and the precipitation appearing during the solidification path of a Co-Ni-Al-W-Ta-Ti-Cr gamma/gamma' cobalt-based superalloy processed by directed energy deposition (DED). Observations reveal characteristic elements partitioning in the liquid during additive manufacturing. Due to this microsegregation, complex multiphase precipitation occurs and the various precipitates are identified and characterized in a cobalt -based superalloy fabricated by DED. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are used to investigate the spatial distribution and nature of the various phases detected in the as -fabricated microstructure. Energy dispersive X-ray spectrometry (EDS), wavelength dispersive X-ray spectrom-etry (WDS), and electron energy loss spectroscopy (EELS) are coupled with a fine analysis of the diffraction patterns to identify the different phases decorating the interdendritic regions. These characterizations allow the identification of different submicronic precipitates: Al2O3, (Ta,Ti)(N,C), HfO2, Cr3B2 and (Ti,Zr,Hf)2SC. The solidification sequence is discussed at light of the experimental results. This work provides a first understanding of the interplay between solidification segregations and the formation of second phase precipitation in a cobalt -based superalloy processed by DED.