Cyclic Fatigue Behaviour of Glass-Infiltrated Ceramics Under Different Environments

Objective: Determine the cyclic fatigue behavior of glass-infiltrated alumina-based (IA- In-Ceram Alumina) and zirconia-reinforced (IZ- In-Ceram Zirconia) ceramics under dry and wet environments.

Methods: IA and IZ specimens were fabricated according to the ISO6872 standard and manufacturer's instructions and polished through 1µm alumina abrasive. The initial strength was determined by fracturing the samples in a 3-point bending setup. The cyclic fatigue was examined in dry and wet conditions by applying a sinoidal stress at 10Hz and a constant maximum stress of 264MPa and 316MPa for the IA and IZ samples, respectively.

The subcritical crack growth (SCG) parameters at cyclic conditions were obtained from the strength (σ_c)and lifetime Weibull distributions of IA and IZ specimens. The fatigue behavior was described using Wohler diagrams that show the effect of the maximum stress applied during loading (σ_max) on the number of cycles to failure (N_f).

Results: Subcritical crack growth occurs at higher maximum stress intensity factors (K_Imax) for IZ as compared to IA samples. For IZ specimens, subcritical crack growth was greater when tested in water.

Based on the initial strength and the calculated fatigue data for all specimens, we estimate an average lifetime of, respectively, 1.57 x 10⁸, 1.70 x 10⁷, 1.75 x 10⁶ and 8.70 x 10⁵ cycles for the IZ dry, IZ wet, IA dry and IA wet specimens if a maximum stress of 150 MPa is applied.

Conclusions: The lifetime under cyclic loading of IZ ceramics decreases significantly in water, which supports the concept of avoiding contact of the IZ material with water. The higher K_Imax needed to promote subcritical crack growth in the IZ samples indicates that zirconia-reinforced ceramics are less prone to failure due to fatigue under cyclic loading conditions.