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 (TiCN np ) on α-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% TiCN np notably reduced α-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 α-Al with the addition of TiCN np (18.2 μm) was approximately twice as large as that without nanoparticles (9.8 μm). Concurrently, the primary dendrite growth rate of α-Al without nanoparticles exceeded that with TiCN np by approximately 15 times. This discrepancy can be attributed to the coarser dendrite tip of α-Al induced by TiCN np , 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 TiCN np was only one-tenth of that observed with Al–5Ti–1B. Consequently, the incorporation of TiCN np 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 TiCN np in Al–Si alloys.