Fracture toughness, strength and slow crack growth in a ceria stabilized zirconia – alumina nanocomposite for medical applications
Mechanical properties and slow crack growth (SCG) behavior of a 10Ce-TZP/Al2O3 nanocomposite cur- rently developed as a biomaterial are considered. Fracture toughness is determined for sharp, long (double torsion) and short (indentation) cracks and a good agreement is found between the two types of cracks. The main toughening mechanism in the nanocomposite is the tetragonal to monoclinic phase transformation of the ceria-stabilized zirconia (Ce-TZP) phase. Transformation at the surface of ground specimens leads to surface compressive induced stresses and an increase in strength. Crack velocity curves (V–KI curves) are obtained under static and cyclic fatigue using the double torsion method. The static V–KI curve in air reveals the three stages characteristic of stress corrosion with a threshold KI0w4.5 MPam1/2 and a fracture toughness of 8.8MPam1/2 significantly higher than those of currently used inert bioceramics (i.e. alumina and Y-TZP). A crack growth accelerating effect is shown under cyclic loading, correlated with a decrease in the threshold. However, the cyclic fatigue threshold (4 MPam1/2) still stands above that of current biomedical grade alumina and zirconia.