Direct evidence of the formation mechanisms of TiC nanoparticles and Al3Ti intermetallics during synthesis of an Al/TiC metal matrix nanocomposite

Microstructure control of in situ metal matrix nanocomposites (MMNCs) poses a barrier to their large-scale production. Here, we interrogate in unprecedented detail the formation mechanisms, morphologies, and microstructures of an in situ Al/TiC MMNC processed via salt flux reaction. Through synchrotron-based X-ray nanotomography (TXM) and scanning and transmission electron microscopy, we visualize in over five orders-of-magnitude of length-scale the TiC nanoparticles, Al 3 Ti intermetallics, and their co-locations. 3D reconstructions from TXM revealed a surprising variety of Al 3 Ti morphologies, including an orthogonal plate structure. By combining our experimental results with phase-field simulations, we demonstrate that this growth form originates from the intermetallic nucleating epitaxially on a TiC particle which is larger than a critical size at a given undercooling. Yet TiC particles that are too small to nucleate Al 3 Ti can also impact the growth of the intermetallic, by splitting the intermetallic plates during solidification. These insights on the divalent roles of the nanoparticles offer general guidelines for the synthesis and processing of MMNCs.