Preparation, microstructure and mechanical property of double-layered metal-ceramic hollow spheres

Abstract The novel double-layered metal-ceramic hollow spheres made of 316L stainless steel powder and Al2O3 hollow spheres were sintered by powder metallurgy method at 1100 °C, 1150 °C and 1200 °C for 3h under vacuum condition in this study. The characteristics of double-layered metal-ceramic hollow spheres were investigated by X-ray diffractometer (XRD), optical microscope (OM) and a field emission scanning electron microscopy (FE-SEM) equipped with an energy dispersive spectroscopy (EDS). And the mechanical properties of hollow spheres were carried out via uniaxial compressive tests. The experimental results showed that metal-ceramic hollow spheres with smooth surface macrograph were prepared under 1200 °C sintering temperature and the interface between metal and ceramic layers was well combined without obvious gap. The porosity of metal layer decreased with increasing sintering temperature. Secondary phases, such as σ phase, carbide and NbS, formed in 316L stainless steel metal layer during supersolidus liquid phase sintering process at 1200 °C sintering temperature. Compressive engineering stress-stain curve of hollow spheres with optimal preparation process showed platform area and the compressive strength of this hollow sphere was 9.84 MPa. The deformation mechanism of metal-ceramic hollow spheres sintered at 1100 °C and 1150 °C was brittle shear fracture, while that of hollow spheres sintered at 1200 °C was plastic deformation. Correspondingly, the failure modes of hollow spheres changed from shear fracture to plastic deformation and densification of hollow shell structures as sintering temperature rose. The fracture characteristics of hollow spheres were also discussed.