Microstructural Characterization of In Situ Aluminum Matrix Composites with Interconnected Aluminum Nitride Produced by Arc Plasma-Induced Accelerated Volume Nitridation

We present a strategy for fabricating aluminum (Al) matrix composites (AMCs) reinforced with interconnected aluminum nitride (AlN) via arc plasma-induced accelerated volume nitridation. AMCs with 10 vol.% AlN are formed in situ by the reaction between liquid Al alloy and nitrogen gas within 1 min of arc melting, revealing very high formation rate of AlN (3.28 × 10⁻¹ g/min·cm³). The rapid nitridation is attributed to the improved wettability and spontaneous infiltration of the melt, which results in the formation of AlN agglomerates and lamellas. In particular, Al-12Si/AlN composites exhibit over two times higher yield strength (195 MPa) than the Al/AlN composites (70 MPa) when compressed along the longitudinal direction to the lamellas. The coefficient of thermal expansion (CTE) is about 30% lower in the Al-12Si/AlN composites (17.0 × 10⁻⁶/K) than pure Al (23.6 × 10⁻⁶/K). This is attributed to the interconnected AlN architecture and Al–Si eutectic microstructure, which constrain the thermal expansion of the Al matrix. The present AMCs afford an attractive combination of specific thermal conductivity and CTE. These findings would facilitate the development of novel AMCs reinforced with interconnected AlN as cost-effective heat sink materials.