Investigation on the thermodynamic stability of phases evolved in Al-based hybrid metal matrix composite fabricated using in-situ stir casting route

Abstract

The objective of this study is to investigate the thermodynamic stability of different phases evolved during fabrication of Al-12wt%Si-(TiB2 + Al2O3) hybrid composite using in-situ stir casting technique. The hybrid composite was fabricated using an approach that involved exothermic reactions between K2TiF6 and H3BO3 salts with the aluminium melt. Microstructural characterization and thermodynamic analysis of the fabricated composite was successfully carried out to confirm and investigate the evolution of phases in the composite respectively. The investigation of the reaction mechanism in the (Aluminium-Titanium-Boron) ternary and (Aluminium-Titanium-Boron-Silicon) quaternary systems was conducted by utilizing the Wilson model and Extended Miedema model to evaluate the excess Gibbs free energy. TiB2 was found out to be the most stable phase in the study followed by AlB2. Silicon being used as alloying element was found to largely hinder the formation of Al3Ti and to some extent also for AlB2. Incorporating silicon caused the excess Gibbs free energy for Al3Ti to become positive after reaching a temperature of 1070 K, which effectively prevented the formation of Al3Ti at higher temperatures. The formation of TiB2 was seen to be unaffected by the addition of silicon in the aluminium melt. The findings from this investigation may be helpful in the development of processing parameters to optimize the microstructure and properties of the composite and can also provide valuable information about specific temperatures at which reactions occur. This can simplify the experimental process and may result in saving of time and resources.