Effect of alumina particle size on densification kinetics and thermal expansion of Cu–Al 2 O 3 composites processed by powder metallurgy

Abstract The influence of reinforcement particle size on the densification behavior, mechanical performance, and thermal expansion of Cu–Al 2 O 3 composites processed by powder metallurgy is systematically investigated in this study to elucidate its role in densification kinetics and thermomechanical performance. Although ceramic-reinforced copper composites have been widely studied, the combined effect of particle size across micron- to nanoscale regimes on densification kinetics and thermal expansion remains insufficiently understood. In this work, alumina particles with average sizes of 40 µ m, 1 µ m, and 50 nm were incorporated into spherical copper powders at volume fractions ranging from 3 to 10%. The mixtures were compacted at 500 MPa and sintered at 1000 °C under a reducing atmosphere. Densification was evaluated using geometric measurements and dilatometry, while microstructural features were analyzed by scanning electron microscopy, and mechanical performance was assessed by compression testing. The results demonstrate that particle size critically governs densification mechanisms and final properties. Composites reinforced with coarse alumina particles exhibited higher densities and more homogeneous microstructures, whereas submicron and nanometric particles promoted agglomeration, limiting particle rearrangement, reducing shrinkage, and increasing residual porosity, which in turn decreased the densification rate. Additionally, the coefficient of thermal expansion was reduced by up to approximately 40% compared to pure copper for composites reinforced with coarse particles. These findings highlight that the use of reinforcement particles comparable to or larger than the matrix powders is a key processing strategy to enhance densification and achieve balanced thermomechanical performance in Cu–Al 2 O 3 composites.