Impact of structure and flow-path on in situ synthesis of AlN: Dynamic microstructural evolution of Al-AlN-Si materials

The Al-AlN-Si composites were prepared in the gas-in-liquid in situ synthesized flow-reaction-system, which was implemented by a powder metallurgy and reaction sintering route. The experimental results showed that Al-AlN-50Si^B material (prepared by ball-milling powders) and Al- AlN-50Si^M material (prepared by mixing powders) exhibited the semi-continuous Si structures and the isolated Si islands, respectively. Subsequently, the Al-AlN-50Si materials were selected as the model materials by phase identification and microstructure analysis. The dynamic microstructural evolution of Al-AlN-50Si materials was investigated using the computational fluid dynamics (CFD) method. Mathematical models and simulation results showed that the in situ synthesis of AlN was strongly influenced by the structure and the flowpath ((cg,N2/lg,N2)+(cs,AlN/ls,AlN)). The flow paths of Al-AlN-50Si^B material were restricted by the semi-continuous Si. These Si structures can promote the formation of the strong turbulence with gradually weakened fluctuation, so that the in situ synthesis of AlN was interconnected and surrounded by an interpenetrating Si network. In contrast, the flow paths of Al-AlN-50Si^M material can easily pass through the isolated Si due to its mild turbulence with linear relationship. As a result, AlN was separated by the isolated Si and agglomerated in the matrix. Overall, the present work provides new insights into dynamic microstructural evolution in in situ reaction sintering systems.