From ceramic core to metal rich surface: functionally graded Al2O3-Ni composites fabricated by centrifugal gel casting

Abstract

Functionally graded Al2O3-Ni composites were fabricated by centrifugal gel casting using a suspension with a total solid loading of 55 vol.% and a metallic phase content of 10 vol.% Ni. The applied centrifugal field induced a pronounced radial redistribution of the metallic phase, resulting in a three-zone microstructure consisting of a Ni-rich outer region, a transition zone, and a ceramic-dominated inner region. Archimedesʼ measurements revealed a high relative density of 99.24 ± 0.74%, low open porosity of 3.54 ± 0.52%, and minimal water absorption of 0.79 ± 0.10%, confirming effective densification. Linear shrinkage after sintering at 1400°C in an Ar/H₂ atmosphere was 13.67% in the axial direction and 13.30% in the radial direction, corresponding to a volumetric shrinkage of 35.24%. Quantitative image analysis showed a local nickel volume fraction of up to 23% in the outer zone and approximately 1% in the inner zone. The mean equivalent diameter of Ni particles ranged from 1.77 to 2.08 μm, depending on the radial position. The alumina matrix exhibited a fine-grained microstructure with a mean grain size of 0.43 ± 0.21 μm. EDS analyses confirmed a smooth compositional gradient and chemical stability of the Al2O3-Ni interfaces without secondary phase formation. These results demonstrate that centrifugal gel casting is an effective method for producing dense, chemically stable, and functionally graded ceramic-metal composites with a controlled microstructural architecture.