In Situ Al-TiC Composites Fabricated by Self-propagating High-Temperature Reaction: Insights on Reaction Pathways and Their Microstructural Signatures

Abstract

In this study, we have analyzed the formation mechanisms and processing-microstructure relationships for Al/TiC metal matrix nanocomposites produced in situ via thermite-assisted (e.g., CuO) self-propagating high-temperature synthesis (SHS). Al/TiC composites were created by reacting Al-Ti-C-CuO pellets in an Al melt using a wide variety of processing conditions (e.g., precursor powder amounts, bulk melt temperature, precursor powder size, pellet packing method). As-cast composites were visualized using both 2D (SEM) and 3D (TXM) microscopy techniques, to study TiC particle and secondary precipitate (e.g., Al3Ti) characteristics at the nanoscale. SHS-produced samples reveal complex microstructures consisting of individual and clustered TiC particles, elongated Al3Ti intermetallics, and C-rich regions surrounded by TiC. Based on a thermodynamic analysis and our microstructural observations, we propose three dominant TiC formation pathways, each resulting in a distinct microstructural signature. Finally, we utilize multivariate statistics (canonical correlations) on the full breadth of imaging data to infer the dominant processing variables (i.e., amount of CuO and C) that most strongly influence TiC particle characteristics and the final composite microstructure. We also discuss how the dominant processing variables relate to the proposed formation pathways and how they may inform the rational design of future composites produced via thermite-assisted SHS.