Spark plasma sintered Al-based composites reinforced with BN nanosheets exfoliated under ball milling in ethylene glycol

Herein we demonstrate the promise of hexagonal BN nanosheets (BNNSs) as fillers in metal matrix composites (MMCs). Al-based MMCs with 1, 5 and 10 wt% of BNNSs were obtained by spark plasma sintering using BNNSs (approximately 300 × 600 nm² and 20–50 nm thick) exfoliated under ball milling in ethylene glycol. Particular attention was paid to the optimisation of ball milling process in various media to achieve a high yield of high-quality BNNSs. The resulting Al-BNNSs composites consisted of Al grains separated by BN layers with a widely varied width from 20 nm to 1–2 µm. Within these layers, individual h-BNNSs, approximately 5–10 nm thick and up to 200 nm long, were mostly oriented in parallel to the Al grain boundaries. The maximum tensile strength of 152 MPa was obtained for a sample with 1 wt% of BNNSs, hereby demonstrating a 69% increase compared to pristine Al. Thorough structural investigation showed that Al grains and BN layers had exhibited strong cohesion to each other and withstood high applied loads. Using SEM and high-resolution TEM analysis of fractured surfaces direct experimental evidence of BNNSs involvement into the deformation process through taking over most of the load was obtained.