Characteristic and function of the dynamic Al-AlN core-shell structure in Al-Al2O3 composite at elevated temperature

An Al-AlN core-shell structure with spatial confinement effect is set up in Al-Al ₂O ₃ composite by pre-nitriding at 580 °C in flowing nitrogen. Its detailed characteristic and function evolution was examined over the temperature range from 600 °C to 1500 °C. With the temperature increase, the as formed Al-AlN core-shell structure in the composite undergoes two typical stages. First, from 660 °C to 900 °C, AlN shell is intact and serves as an “eggshell” to localize the molten Al core inside. When the temperature rises above 900 °C, AlN shell begins to crack under thermal stress, and the micronized Al cluster (mixture of droplets and vapor) was extracted out gradually. In this period, AlN shell serves as a slowly-released structure to control the gradual exposure of Al core and their conversion to highly-reactive micronized Al(l) and Al(g). On this basis, the controllable synthesis of AlN-based reinforcements can be realized by adjusting the nitriding path of Al with different states and scales. The detailed analysis of the dynamic Al-AlN core-shell structure at elevated temperature contributes to the better phase and morphology control of the Al-Al ₂O ₃ composite for metallurgy.