Microstructural and mechanical characterization of ceria-stabilized tetragonal zirconia/alumina composites produced through a segregated-network approach for ceramic bushing applications

Abstract

The aim of this study was to develop ceramic bushings used in automotive engineering. To achieve this, 12 mol% ceria (CeO2)-stabilized tetragonal polycrystalline zirconia (12Ce-TZP)/10-20 wt% alumina (Al2O3) composites were designed by using a segregated-network approach. They were subsequently produced by wet-mixing, cold isostatic pressing (CIP), computer numerical control (CNC) machining, binder burnout, and sintering at 1550-1600 degrees C for 1-3 h. Physical, mechanical, and microstructural properties of 12Ce-TZP/Al2O3-sintered composites were characterized using the Archimedes' principle, Vickers hardness (HV), indentation fracture toughness (K-Ic), flexural strength (sigma), X-ray diffraction (XRD), ultra-high-resolution scanning electron microscopy (UHR-SEM), and energy-dispersive X-ray spectroscopy (EDX) analyses. According to the overall results, 12Ce-TZP/Al2O3 composites were sintered up to 99.5% of theoretical density, when sintering temperature and dwell time were increased. 12Ce-TZP/10 wt% Al2O3/1600 degrees C/2 h composite, showing high mechanical properties in HV = 9.52 +/- 0.09 GPa, K-Ic = 15.44 +/- 0.15 MPa m(1/2), and sigma = 955.41 +/- 15 MPa, was considered the most appropriate composition for ceramic bushing production. XRD analyses indicated that 12Ce-TZP/Al2O3 composites consisted of tetragonal zirconia (t-ZrO2) and corundum (alpha-Al2O3) phases, while 12Ce-TZPs were found to contain only t-ZrO2 phase with no trace of monoclinic zirconia (m-ZrO2). UHR-SEM investigations revealed that the microstructural evolution of 12Ce-TZP/Al2O3 composites was observed as an interpenetrated intragranular-type through the formation of a segregated-network structure. In addition, energy-absorbing mechanisms, i.e., crack propagation hindrance, crack blunting, crack bridging, crack deflection, and stress-induced t-ZrO2 -> m-ZrO2 phase transformation were seen to govern the enhancement of mechanical properties. It is thought that results presented herein are also significant for new commercial applications of 12Ce-TZP/Al2O3 composites rather than other biomaterials.