Piza Mariana M T, Bergamo Edmara T P, Campos Tiago M B, Carvalho Laura F, Goulart Celso A, Gutierres Eliezer, Lopes Adolfo C O, Benalcazar Jalkh Ernesto B, Bonfante Estevam A
Department of Prosthodontics and Periodontology, University of São Paulo, Bauru School of Dentistry, Bauru, SP, Brazil.
Department of Prosthodontics and Periodontology, University of São Paulo, Bauru School of Dentistry, Bauru, SP, Brazil.
Dent Mater. 2023 Nov;39(11):1022-1031. doi: 10.1016/j.dental.2023.09.005. Epub 2023 Sep 27.
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.
Disc-shaped specimens were obtained through uniaxial pressing of a commercial ATZ powder comprised of 80%ZrO / 20%AlO, with a particle size of 50 nm and 150 nm, respectively. Sintering was performed at 1500ºC 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 ºC 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.
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.m. 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.
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 nanocomposite was susceptible to hydrothermal degradation. Further studies are required to evaluate its degradation kinetics at low temperatures.
制备氧化铝增韧氧化锆（ATZ）纳米复合材料，并表征其在两种不同人工老化方法前后的晶相、微观结构、残余应力、力学性能和光学性能。
通过对由80%ZrO/20%AlO组成、粒径分别为50nm和150nm的商用ATZ粉末进行单轴压制获得圆盘形试样。在1500ºC下烧结2小时。根据老化方案分为即刻组（ATZ-I）以及在高压釜（ATZ-A）或水热反应器（ATZ-R）中于134ºC、2.2巴下老化20小时的组。分别通过X射线衍射（XRD）和扫描电子显微镜（SEM）评估晶相和微观结构。通过拉曼光谱评估残余应力。计算对比度（CR）和透明度参数（TP）以表征光学性能。通过维氏显微硬度、断裂韧性和双轴弯曲强度测试分析力学性能。
两种老化方案的XRD光谱均显示存在单斜氧化锆（20-31%），其中在水热反应器中老化后观察到更高的相变。光学性能评估显示高不透明度（CR：0.99）和遮盖能力（TP：0.26），老化后无显著差异。拉曼光谱证明老化组中存在残余压应力，ATZ-R组（-215.2MPa）显著更高。烧结后的试样显示硬度约为12.3GPa，断裂韧性约为1.9MPa·m。ATZ-I组的特征强度为740MPa，ATZ-A组为804MPa，ATZ-R组为879MPa，组间存在显著差异。威布尔模量范围为16.5至18.8。所有组在高达500MPa应力任务下均表现出高可靠性（99-100%），老化后无显著差异。
实验性ATZ纳米复合材料具有高不透明度和高威布尔模量。虽然老化产生了导致特征强度增加的内部压应力，但该纳米复合材料易受水热降解影响。需要进一步研究以评估其在低温下的降解动力学。
