Alumina-toughened zirconia nanocomposite: Aging effect on microstructural, optical, and mechanical properties

Author(s)

Piza, Mariana M. T. ; Bergamo, Edmara T. P. ; Campos, Tiago M. B. ; Carvalho, Laura F. ; Goulart, Celso A. ; Gutierres, Eliezer ; Lopes, Adolfo C. O. ; Jalkh, Ernesto B. Benalcazar ; Bonfante, Estevam A.

• Document type: Journal article
• Source: Dental Materials; v. 39, n. 11, p. 10-pg., 2023-10-14.

Abstract

Objectives: To process an alumina-toughened zirconia (ATZ) nanocomposite and to characterize its crystalline phases, microstructure, residual stress, mechanical and optical properties before and after two different artificial aging methodologies. Methods: Disc-shaped specimens were obtained through uniaxial pressing of a commercial ATZ powder comprised of 80%ZrO2 / 20%Al2O3, with a particle size of 50 nm and 150 nm, respectively. Sintering was performed at 1500 degrees C for 2 h. Groups were established according to the aging protocol as immediate (ATZ-I) and aged either in autoclave (ATZ-A) or hydrothermal reactor (ATZ-R) at 134 degrees C for 20 h at 2.2 bar. Crystalline phases and microstructure were assessed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Residual stress was evaluated by Raman spectroscopy. Contrast Ratio (CR) and Translucency Parameter (TP) were calculated to characterize optical properties. Mechanical properties were analyzed through Vickers microhardness, fracture toughness, and biaxial flexural strength test.Results: XRD spectra of both aging protocols revealed the presence of monoclinic zirconia (20-31%), where higher phase transformation was observed after aging in hydrothermal reactor. Optical properties evaluation demonstrated high opacity (CR: 0.99) and masking ability (TP: 0.26), with no significant differences after aging. Raman spectroscopy evidenced the presence of residual compressive stresses in the aged groups, being significantly higher for ATZ-R (-215.2 MPa). As-sintered specimens revealed hardness of-12.3 GPa and fracture toughness of-1.9 MPa.m1/2. Characteristic strength was 740 MPa for ATZ-I, 804 MPa for ATZ-A, and 879 MPa for ATZ-R, with significant differences between groups. Weibull modulus ranged from 16.5 to 18.8. All groups demonstrated high reliability up to 500 MPa stress missions (99-100%), with no significant differences after aging.Significance: The experimental ATZ nanocomposite presented high opacity and a high Weibull modulus. While aging created internal compressive stress responsible for an increase in characteristic strength, the nano-composite was susceptible to hydrothermal degradation. Further studies are required to evaluate its degradation kinetics at low temperatures. (AU)

• FAPESP's process: 12/19078-7 - Development and processing of Al2O3-ZrO2 translucent composite for CAD/CAM monolithic prostheses: the effect of aging on biaxial flexural strength
• Grantee: Estevam Augusto Bonfante
• Support Opportunities: Research Grants - Young Investigators Grants
• FAPESP's process: 19/14798-0 - Development of pre-sintered ZTA 80% Al2O3/20% ZrO2 composite blocks for milling in CAD/CAM system
• Grantee: Adolfo Coelho de Oliveira Lopes
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 16/18818-8 - Multi-User Equipment approved in grant 2012/19078-7: ElectroPuls E3000 Linear-Torsion All-Electric dynamic test instrument package
• Grantee: Estevam Augusto Bonfante
• Support Opportunities: Multi-user Equipment Program
• FAPESP's process: 21/08018-2 - Nanomechanical layer characterization of graded ATZ and ZTA composites
• Grantee: Edmara Tatiely Pedroso Bergamo
• Support Opportunities: Scholarships abroad - Research Internship - Post-doctor
• FAPESP's process: 20/12874-9 - Infiltration graded by glass in an experimental composite based on whiskers of alumina and zircônia: development, microstructural characterization and optical and mechanical properties
• Grantee: Tiago Moreira Bastos Campos
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 19/08693-1 - Experimental glass-infiltrated alumina-zirconia composites: characterization of microstructure, optical and mechanical properties.
• Grantee: Edmara Tatiely Pedroso Bergamo
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 22/07157-1 - Physical and mechanical characterization of a multilayered system using recycled zirconia
• Grantee: Ernesto Byron Benalcazar Jalkh
• Support Opportunities: Scholarships in Brazil - Post-Doctoral