Investigating the Grain Refinement Mechanism of Al-Cu Alloys by TiCN Nanoparticles Through In-Situ X-radiography

The grain refinement of Al alloys achieved by inoculation with nanoparticles, such as Al-Ti-B, has been widely acknowledged. However, the practical effects of using inoculant TiCN nanoparticles (TiCNnp) on grain refinement during solidification have yet to be fully elucidated due to the opaque mechanism of the solidification process. This study investigated the influence of TiCNnp on the evolution of a-Al dendrites in Al-13Cu (wt pct) alloy at different cooling rates utilizing in-situ synchrotron X-radiography. Adding TiCNnp significantly reduces α-Al grain size, reaching approximately 324 μm at a cooling rate of 0.2 K/s. At the same time, the grain growth rate has been dramatically decreasing from 43.7 to 8.1 μm/s. Moreover, the dendrite tip radius of TiCNnp is approximately twice that of Al-Cu. This difference can be attributed to the larger dendrite tip with the addition of TiCNnp, leading to a more pronounced solute accumulation ahead of the dendrite tip. Consequently, the decreased undercooling in front of the dendritic tip results in a smaller driving force hindering primary α-Al dendrites' growth. The results reveal that adding nanoparticles increases grain nucleation while restricting dendritic growth, altering the dendritic grain growth morphology. This investigation provides valuable insights into the grain refinement of Al-Cu alloys by TiCNnp.