Experimental analysis and numerical simulations of the mechanical properties of a (Ce,Y)-TZP/Al2O3/H6A ceramic composite containing coupled toughening mechanisms.

OBJECTIVES: This study investigates the simulation of the mechanical behavior of a bioceramic composite based on (Ce,Y)-TZP reinforced with equiaxed Al2O3 and platelet-shaped hexaaluminate (H6A) grains using Finit Element Method (FEM). METHODS: A commercial (Ce, Y)-TZP/Al2O3 ceramic powder was compacted into disc-shaped specimens that were sintered at 1500 °C for 2 h. The sintered samples were further subjected to hydrothermal degradation in an autoclave at 134 °C, 0.2 MPa, for 10 h and characterized according to their phase composition, microstructure, and relative density. Their flexural strength values were determined by the piston-on-three-ball test, and Weibull statistics was used to evaluate the results. Their hardness, fracture toughness and elastic parameters were also measured. Numerical simulations of the biaxial strength test were performed using the ABAQUS finite element code. RESULTS: The sintered ceramic composite material presented relative density >99%, high resistance to hydrothermal degradation, average hardness of 1435 ± 35 HV, fracture toughness KIC of 9.7 ± 0.5 MPa m1/2, and average biaxial flexural strength of 952.6 ± 88 MPa. The numerical predictions of the biaxial flexural strength showed a consistently lower average biaxial flexural strength value of 880.9 MPa, ∼10% lower than the average experimental results. CONCLUSIONS: The differences observed are attributed to the complex coupled toughness mechanisms of this material, not included in the finite element simulations.

Mechanical properties of ceramic composites based on ZrO2 co-stabilized by Y2O3-CeO2 reinforced with Al2O3 platelets for dental implants.

OBJECTIVES: The objective of this work was the development and characterization of a ceramic composite based on (Ce,Y)-TZP/Al2O3 aiming an application on dental implants, comparing it with conventional monolithic 3Y-TZP ceramics, currently used for the same type of application. METHODS: Ceramic samples, 3Y-TZP (n = 40) and (Ce,Y)-TZP/Al2O3 (n = 40), were sintered at 1500 °C - 2h and characterized by relative density, X-Ray diffraction (XRD) and microstructure. Then, the samples of both materials were divided into two groups: 1) samples with original (as sintered) surfaces; 2) samples with conditioned, polished, surfaces. All samples were submitted to hydrothermal degradation tests, on an autoclave (134 °C - 2 bar), for 10 h in artificial saliva. The degraded samples were characterized by XRD and the polished group were also characterized by their elastic moduli, Vickers hardness and fracture toughness (Vickers indentation method). Both groups were also submitted to a flexural strength test, 3B-P testing, for which the data were interpreted using Weibull statistics. RESULTS: All sintered specimens presented nearly full densification. After the hydrothermal degradation tests, 3Y-TZP samples presented 16.4% of monoclinic (m)-ZrO2 phase while the composite samples withheld 100% of tetragonal (t)-ZrO2 phase. Both materials presented equiaxial ZrO2 grains with an average size of 0.48 ± 0.17 µm and 0.75 ± 0.22 µm, respectively, for the monolithic and composite ceramics. In the composites, is observed the presence of well distributed Al2O3 grains on the ZrO2 matrix, in two distinct morphologies: equiaxial grains and platelets. The composites (Ce,Y)-TZP/Al2O3 presented average values of elastic moduli, Vickers hardness and fracture toughness of 228.3 ± 6.5 GPa, 1427 ± 46 HV e 11.3 ± 0.4 MPa m1/2, respectively. An inversely proportional relationship is observed between the roughness and the bending strength, since the 3Y-TZP samples presented a average strength of 860.7 ± 81 MPa (as-sintered) and 965.4 ± 93 MPa (polished) while the (Ce,Y)-TZP/Al2O3 composites presented average strength of 810.6 ± 147 MPa (as-sintered) and 952.6 ± 88 MPa (polished). CONCLUSIONS: The composites (Ce,Y)-TZP/Al2O3 showed high resistance to degradation in saliva and adequate properties for use as dental implants. Values of flexural strength (>950 MPa) and Weibull modulus (m > 10) were similar to the conventional 3Y-TZP ceramics. Moreover, its hardness, elastic modulus and fracture toughness were higher than those obtained for 3Y-TZP. The expressive values of KIC obtained for (Ce,Y)-TZP/Al2O3 composites are results of association of different toughening mechanisms acting simultaneously in the material.