Refitting of Zirconia Toughening into Open-Cellular Alumina Foams by Infiltration with Zirconyl Nitrate

• Main Authors: Ulf Betke, Marcel Scheunemann, Michael Scheffler
• Format: Article
• Language: English
• Published: MDPI AG 2019-06-01
• Series: Materials
• Subjects: cellular ceramic; ceramic foam; reticulated porous ceramic (RPC); transformation toughening; zirconia-toughened alumina (ZTA); hollow strut infiltration; metal salt infiltration
• Online Access: https://www.mdpi.com/1996-1944/12/12/1886

The present work describes the combination of the well-established dispersion infiltration of the hollow struts in reticulated porous ceramics (RPCs) and the salt solution infiltration of the remaining strut porosity. This approach is applied on alumina foams, which are loaded subsequently with a dispersion of sub-micrometer alumina particles and a ZrO(NO₃)₂ solution. The zirconyl nitrate is converted into a ZrO₂ transformation toughening phase during the final sintering step. As a consequence of the complex microstructure evolution during the consecutive infiltration cycles, the reinforcement phase concentrates selectively at the weak spots of RPC structures—namely, the hollow strut cavities and longitudinal cracks along the struts. As a consequence, a severe improvement of the compressive strength is observed: The average compressive strength, normalized to a porosity of 91.6 vol.%, is 1.47 MPa for the Al₂O₃/ZrO₂ infiltrated foams, which is an improvement by 40% with respect to alumina-only loaded foams (1.05 MPa) or by 206% compared to uninfiltrated alumina RPCs (0.48 MPa). The compressive strength results are correlated to infiltration parameters and the properties of the infiltration fluids, for example the rheological behavior and the size of the Zr solute species in the respective ZrO(NO₃)₂ solution.