In-situ quantitative investigation of the growth inhibition effect of TiCN nanoparticles on primary α-Al in Al-Cu-Si alloys

In-situ synchrotron X-radiography studied the impact of TiCN nanoparticles (TiCNnp) on alpha-Al dendrite morphology and growth in Al-13Cu-7Si alloys. Comparative experiments were conducted without nanoparticles and with the addition of Al-5Ti-1B. Despite Al-5Ti-1B had almost no refining effect, 0.5% TiCNnp notably reduced alpha-Al grain size of Al-Cu-Si alloys, especially at higher cooling rates. When cooled at a rate of 0.2K/s, the dendrite tip radius of alpha-Al with the addition of TiCNnp (18.2 mu m) was approximately twice as large as that without nanoparticles (9.8 mu m). Concurrently, the primary dendrite growth rate of alpha-Al without nanoparticles exceeded that with TiCNnp by approximately 15 times. This discrepancy can be attributed to the coarser dendrite tip of alpha-Al induced by TiCNnp, which led to a greater solute accumulation in front of the tip. Furthermore, the area growth rate of both grain and solute suppressed nucleation zone (SSNZ) with addition of TiCNnp was only one-tenth of that observed with Al-5Ti-1B. Consequently, the incorporation of TiCNnp resulted in a significantly smaller nucleation-free zone, facilitating the activation of a greater number of nucleation sites within the melt. This study sheds light on the growth inhibition mechanism of TiCNnp in Al-Si alloys.