Microwave plasma-produced Al/Al₂O₃ microparticles as precursors for high-temperature high-strength composites

A modern urgent task is to increase the upper limit of peak and operating temperatures of Al-based composites above 400 degrees C, which, due to the combination of low weight and high strength, are in demand in various power units and elements of load-bearing structures. To address this important problem, Al-based composites reinforced with 1, 3, 5, and 10 wt% of submicron Al2O3 particles were spark plasma sintered (SPS) using Al/Al2O3 composite microparticles obtained in microwave argon-plasma. When a mixture of submicron Al and Al2O3 particles is fed into the plasma reactor, the native oxide film on the Al surface is destroyed, Al melts, melt drops merge, and Al2O3 particles, the surface of which is cleaned of contamination by Ar+ ions, are captured by the melt, forming heterogeneous Al/Al2O3 microparticles with a strong Al/Al2O3 interface, which then become structural elements of SPS composites. The introduction of Al2O3 leads to a significant improvement in chemical, mechanical and tribological properties. With the addition of 10 wt% of Al2O3, hardness increases by 90% and ultimate compressive strength (UCS) by 143% (25 degrees C) and 111% (500 degrees C) while maintaining a high strain to failure of approximately 21.5%. Compared to the Al-Al2O3 composite sintered from the non-plasma treated powder, the UCS increases by 16% (25 degrees C) and 33% (500 degrees C). The Al-10%Al2O3 material shows significantly improved tribological characteristics due to the formation of an oxide-based tribofilm, which prevents intensive Al adhesion to the counterbody. In addition, due to the high density of Al2O3 particles, impact wear resistance increases by 2-3 times, the corrosion potential in a chloride-containing medium positively shifts by 110 mV, and the corrosion current density decreases by a factor of three. Achieving a UCS of 423 MPa at 500 degrees C while improving chemical and tribological properties can expand the high-temperature application of Al-based composites.