Interfacial characteristics of dual-phase Si/TiB2 and its crack initiation mechanism in hypereutectic Al-Si alloys

Abstract

Al-17Si-4Cu and 6 wt% TiB2/Al-17Si-4Cu composites are generated using an in-situ reaction in this study. The impact of TiB2 ceramic particles on the morphology, size and distribution of primary Si in the composites and the properties of the composites are studied. Based on the results of transmission electron microscopy, the work of adhesion (Wad), interfacial energy and electronic structure of the TiB2/Si structure are calculated using first-principles calculations. Si-Ti triple bonds are formed at the Ti-terminated stacking model interface, while Si-B double bonds form at the B-termination interface model after structural energy optimization. In the TiB2/Si stacking interface models, the Ti termination model has the highest interfacial bonding strength, a Wad of 2.6 J/m2, the smallest interface distance (d0 = 1.874 Å) and the lowest interfacial energy (0.216 J/m2). The analysis of the interfacial bonding properties indicates the formation of Si-Ti covalent bonds and metal bonds at the Ti-terminated interface. Conversely, weak covalent bonds and ionic bonds are observed at the B-terminated interface model. These findings suggest that the Ti-terminated interface model exhibits significant interfacial stability. The experimental results are verified by first-principles calculations. Finally, in-situ scanning electron microscopy demonstrates that TiB2 can hinder the crack initiation and propagation path change of primary Si in the Al-17Si-4Cu alloy. The modulus and microhardness results show that the addition of TiB2 endows the dual phases of TiB2 and primary Si with a stronger ability to maintain the original morphology and structure, illustrating that they are significantly strengthened by the incorporation of TiB2 particles. This research offers valuable theoretical guidance into the enhancement of ceramic-reinforced aluminum matrix composites.