Factors affecting the mechanical behavior of Y-TZP.

Aim: The aim was to evaluate the influence of sandblasting with various propulsion pressures on the phase transformation, flexural strength and Weibull modulus of a yttria stabilized tetragonal zirconia polycrystalline ceramic (Y-TPZ). In addition, the susceptibility of cyclic loading and low-temperature degradation under two different conditions (chemical and thermal aging) was investigated.

Materials And Methods: The specimens [105bar-shaped specimens (19.3×14.5×1.3mm(3))] were equally divided into seven groups (n=15) according to the test protocols. The specimens in control group received no surface treatment (Group A). Groups B1, B2 and B3 were airborne-particle abraded with 110μm Al2O3 particles at 200kPa, 400kPa and 600kPa (2bar, 4bar and 6bar) pressure, respectively. Group C was submitted to mechanical cyclic loading under 200N 20,000 times sinusoidal loading/unloading at a frequency of 10Hz between 10% and 100% load in distilled water at 37°C. Group D was submitted to thermal degradation in an autoclave at 134°C under additional 200kPa pressure for 5h. Group E was immersed in 4% acetic acid at 80±5°C for 168h as chemical degradation testing. Following each treatment protocols, the three-point flexure test was used to calculate the flexural strength. Additionally, X-ray diffraction analysis was used to estimate the relative amount of monoclinic phase. The reliability of strength was assessed through the Weibull distribution. Statistical analysis was conducted with one-way ANOVA and Tukey׳s pairwise multiple comparisons. The treated and fractured surfaces were observed with SEM.

Results: Statistical analysis revealed that there were significant differences among the flexural strength results of all tested groups (F=4.510, p<0.05). Group B2 demonstrated the highest strength values, whereas Group E showed the lowest (625.86±123.57; 466.56±91.50, respectively). Weibull moduli of all tested groups were statistically significant and ranging from 4.3 to 8.3. A greater amount of monoclinic phase was determined in the specimens of D, E and B3 groups (25.43%, 20.89% and 19.71%, respectively). However, lower amount was observed in groups A, B1 and B2 (10.02%, 13.35% and 15.19%, respectively).

Conclusions: The present study suggested that flexural strength of zirconia was significantly decreased by chemical degradation. In addition, surface conditioning, cyclic fatigue and thermal, chemical degradation conditions significantly changed the structural reliability of the material's strength.