A TEM Study of Cobalt-Base Alloy Prototypes Fabricated by EBM

A novel microstructural architecture consisting of Cr23C6 carbide spatial columns was created in solid components of Co-26Cr-6Mo-0.2C fabricated from powder by additive manufacturing using electron beam melting. These columns of carbides extended in the build direction and are formed by the x-y rastering of the electron beam to pre-heat and melt powder layers using CAD models. These microstructural architectures are similar to rapidly solidified/unidirectionally solidified structures created by heat extraction in the direction perpendicular to the build plane. These columnar carbide architectures were observed by optical metallography and transmission electron microscopy (TEM) and compared with intrinsic stacking fault microstructures observed in annealed components. The TEM analysis allowed the details of the carbide crystal structure and corresponding cubic morphology to be observed.