Revealing the interplay between element mixing, intermetallics, and microcracks in multi-material laser additive manufacturing

Abstract

Additive manufacturing (AM) of multiple metallic materials suffers from microcracks at the dissimilar material interface due to brittle intermetallic compounds (IMCs). While avoiding IMCs through specialized composition design is a conventional approach, the interdependence between molten pool material mixing, IMC characteristics, and microcracks are not well understood. In this work, we compared typical process conditions for laser powder bed fusion of aluminum alloy substrate and Inconel particles. We revealed that the insufficient dissimilar material mixing under the lower energy density condition can exacerbate element clustering, IMC concentration, and cracking. High-speed synchrotron X-ray imaging shows that Ni-rich clusters can abruptly plunge into the molten pool to cause localization of IMCs and microcracks. In the high energy density case, the keyhole oscillation can disperse the Ni-rich clusters and suppress cracks but lead to keyhole porosities. Microstructural characterization and multiphysics simulations support the X-ray imaging observations. We propose that control of molten pool flow to enhance mixing while preventing porosities is the key to crack-free AM of metallurgically incompatible dual alloys.