On the mechanism of Si-promoted destabilization of TiC x particles in Al alloys

TiC x is an excellent composite strengthening particle and grain refiner for Al alloys. However, the stability of TiC x is poor when solute Si exists in Al alloy melts, which significantly depresses its strengthening and grain refining effects. In this work, the destabilization mechanisms of the TiC x particles in Al-Si alloy melt with a composition of Al-7Si-7.5TiC were explored via experiments, first-principles calculations and thermodynamic calculations. The experimental results show that Si atoms diffuse into TiC x and Ti atoms are released into the Al melt to form a Ti-rich transition zone during the insulation of TiC x in Al-Si melt, and the TiAl y Si z and Al 4 C 3 phases are solidified in the Ti-rich zone and at Ti-rich zone/TiC x interface, respectively. The first principles calculations show that the low formation energy of C vacancies facilitates the rapid diffusion of Si atoms in TiC x , while the doping of Si atoms reduces the energy barrier of diffusion of Ti atoms in TiC x and promotes the formation of Ti-rich zones. The thermodynamic calculations show that the wide crystallization temperature range of the destabilized product TiAl y Si z phase is the key to continuous decomposition of TiC x particles. In addition, the driving force of the main destabilization reaction of TiC x in the Al-Si alloys is about 44 times higher than that in the Al alloys without Si addition. This indicates that the presence of solute Si remarkably promotes the subsequent decomposition process of TiC x in the Al-Si alloy melts. & COPY; 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.