Structural Synergy of NanoAl₂O₃/NanoAl Composites with High Thermomechanical Properties and Ductility

Achieving a combination of high strength and ductility in metal-based composites is still a difficult task, and it is especially challenging in a wide temperature range. Here, nanoAl₂O₃/nanoAl composites with high tensile and compressive strength and excellent ductility at 25 and 500 °C were obtained using Al and Al₂O₃ nanopowders via a combination of high-energy ball milling (HEBM) and spark plasma sintering (SPS). Being about three times lighter than conventional high-strength steel (with a density of 2.7 g/cm³ vs. that of 7.8 g/cm³ for steel), the nanoAl₂O₃/nanoAl materials demonstrated tensile strength and elongation before failure comparable with those of steel. The nanoAl₂O₃/nanoAl composites were strengthened with two types of Al₂O₃ NPs, in situ formed, and introduced into the powder mixture. The resulting materials had a bimodal microstructure consisting of Al with micron and submicron grains surrounded by an Al/Al₂O₃ framework whose structural components were all in the size range of 20–50 nm. Among the studied compositions (0, 1, 2, 3, 4, 5, 10, and 20 wt.% of Al₂O₃), the Al-3%Al₂O₃ material showed the best thermomechanical properties, such as a tensile strength of 512 MPa and 280 MPa and a compressive strength of 489 MPa and 344 MPa at 25 and 500 °C, respectively, with an elongation to failure of 15–18%. These results show the promise of nanoAl₂O₃/nanoAl composites for use as small items in the automotive and aviation industries.