Direct correlations between fracture toughness and grain boundary segregation behavior in ytterbium-doped magnesium aluminate spinel

The effect of ytterbium (Yb) on magnesium aluminate spinel (MgAl2O4) grain boundary structure and strength has been evaluated using mechanical testing and electron microscopy. Bicrystal specimens were prepared by hot pressing. Certain interfaces were doped with Yb prior to bonding. Interfaces were characterized using atomic-resolution high-angle annular dark-field imaging. Interface fracture toughness was determined using a microscale cantilever beam test. A 30% increase in fracture toughness was found to correlate with grain boundary Yb segregation.