Ceramic particles, such as SiC and Al2O3, have been used to reinforce Al alloys to improve their strength and wear-resistance. However, previous studies mainly dealt with either relatively large hard particles (from tens to hundreds of micrometers in diameter) or nanometer-sized particles with low volume fractions (a few percent). In this study, near-fully-dense (97–99%) Al2O3-Al nanocomposites with higher particle concentrations (5–15 vol%) were processed using mechanical alloying and hot isostatic pressing. Transmission electron microscopy revealed very high dislocation density in aluminum matrix for these Al2O3-Al nanocomposites. High strength (σ0.2%: ∼500 MPa) and encouraging tribological properties have been observed. The Al2O3(15 vol%)-Al nanocomposites performed unexpectedly well when sliding against 52100 bearing steel. The friction coefficient of the nanocomposite was 55%, 37%, and 55% lower and the wear-resistance was 1500X, 30X, and 120X higher than those of pure Al, cast Al 319 alloy, and conventional Al2O3-Al composites, respectively. Wear scar examination showed severe adhesive wear on the conventional Al alloy and micro-composite surfaces; however, only mild abrasive wear was observed on the nanocomposite surfaces. It was observed that the particle concentration had to exceed a critical level (10–15 vol%) to exhibit superior wear-resistance, even though a lower level (e.g. 5 vol%) resulted in a significantly improved tensile strength.

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