Effect of Copper Powder Morphology on Microstructure, Densification, and Mechanical Properties of Al2O3-Cu-Ni Composites Fabricated by Spark Plasma Sintering

To investigate the influence of copper particle morphology and size on microstructure, densification, and mechanical properties, Al2O3-Cu-Ni ceramic-metal composites containing 15 vol.% metallic phase (7.50 vol.% Cu and 7.50 vol.% Ni) were fabricated by spark plasma sintering (SPS). Two composite Series were produced using either spherical copper powder (Sigma-Aldrich) or dendritic copper powder (Createc), while keeping all other processing parameters constant. Both composites exhibited high densification when sintered at 1300 °C. However, the spherical Cu powder achieved a near-theoretical density of 99.99%, while the dendritic Cu powder yielded a slightly lower relative density of 99.13%. This difference is attributed to less efficient packing and locally trapped porosity. Microstructural analyses (SEM, STEM, and EDS) revealed that spherical Cu particles promoted fine, homogeneous dispersion of compact Cu-Ni-rich regions within the Al2O3 matrix. In contrast, dendritic Cu particles led to irregular, elongated, and partially interconnected metallic networks. These differences significantly affected mechanical behavior. Series I (spherical Cu) exhibited higher Vickers hardness (15.60-16.20 GPa) and a stable increase in fracture toughness from 4.74 to 5.62 MPa m0.5 with increasing load. Series II (dendritic Cu) showed lower hardness (12.60-14.70 GPa) but exhibited enhanced load-dependent toughening. Fracture toughness increased to 5.09 MPa m0.5 at the highest load. Compression tests revealed a significant morphology effect. Spherical Cu powder (Series I) produced a stable force-displacement response and a peak force of 2.25 kN. In contrast, dendritic copper powder (Series II) resulted in delayed load bearing, unstable post-peak behavior, and a maximum force of 1.10 kN, which is approximately half that of Series I. These results demonstrate that the morphology of copper powder is a key parameter for tailoring the balance between hardness and fracture toughness in SPS-processed Al2O3-Cu-Ni composites.