On the banded microstructures in CoCrMo-Ni in-situ alloyed through laser powder bed fusion

Heterogenous banded microstructure was observed throughout a compositionally graded CoCrMo-Ni alloy using mixed CoCrMo and Ni powders and the laser powder bed fusion (LPBF) technique. Such a banded structure is a result of the melt pools having large depth-to-width aspect ratio, which favors grain growth towards its center. A continuous alignment of the growing grains towards the temperature gradient makes them appear to be 'chasing' the trailing edge of the melt pool. Therefore, the observed grain morphology varies with the viewing direction, which, in combination with the scan rotation of 67, results in the appearance of an alternating grain morphology along the build direction. These findings bring attention to the new possibility of tailoring heterogeneous grain structures that can enhance the mechanical properties of the AM parts. This approach can be readily applied to other types of alloys, thereby enriching the alloy design tools available for microstructural engineering.