Characterization of C795 alumina ceramic hollow spheres and their Cu modified and Cu coated versions

This study compares the structural characteristics and single-particle compression behavior of four hollow-sphere filler types, including commercial C795 alumina ceramic hollow spheres (CHSs, >95 wt% Al 2 O 3 ), Cu-modified ceramic hollow spheres (MCHSs), and their Cu-coated versions (CuCHSs and CuMCHSs), from the viewpoint of metal matrix syntactic foam (MMSF) filler design. The structural and mechanical properties of the hollow spheres were analyzed using SEM-EDS, XRD, single-particle compression tests, and Weibull analysis of hollow sphere strength. The results show that increased wall thickness (t) and relative wall thickness (t/D) of the Cu-coated hollow spheres increase their absolute crush force. Compared to the uncoated samples, the average crush force (F crush ) of CuCHSs and CuMCHSs increased by approximately 31% and 40%, respectively. However, these single-particle results should be interpreted as filler-level indicators rather than direct predictors of the bulk compressive response of MMSFs, because the latter is also controlled by particle packing, inter-particle interaction, matrix constraint, load sharing and interface quality. XRD results show additional peaks that can be assigned to CuAl₂O₄, suggesting the possible formation of a copper aluminate spinel-related phase during the commercial modification process. The results provide an experimental basis for selecting and designing hollow-sphere fillers for MMSFs.