Densification Behaviour and Mechanical Properties of Aluminium Oxide and Cerium Oxide-Doped Yttria Tetragonal Zirconia Polycrystal Ceramics Using Two-Step Sintering
The densification behaviour, mechanical properties, and microstructure of high-purity Al2O3 and CeO2-doped Y-TZP with different weight percentage varied from 0.3 to 1？wt% were investigated. The samples were pressed uniaxially at 200？MPa into rectangular bars and discs and pressureless-sintered at temperature ranging between 1250°C and 1450°C for 2？h while the microstructure was characterized with a scanning electron microscope (SEM). Two-step sintering process works well for temperature higher than 1400°C and it created most tetragonal phase arrangement for stable structure to delay ageing through phase transformation. The mechanical properties in terms of bulk density, Young’s modulus, Vickers hardness, and fracture toughness were also measured. The results indicate that the addition of dopants accelerated the densification parameters and reinforced and toughened the obtained bodies. The maximum values for the mechanical properties of the Al2O3 and CeO2-doped Y-TZP ceramics were 6.01, 220？GPa, 13.8？GPa, and 7？MPa for density, Young’s modulus, Vickers hardness, and fracture toughness, respectively, which are higher than those of the doped samples. 1. Introduction Yttria-stabilised tetragonal zirconia polycrystalline ceramics (Y-TZP) are becoming popular engineering materials due to their excellent mechanical properties, studied and used in many engineering applications, such as engine parts, valves, cutting tools, and moulds, due to their good fracture toughness, high strength, elastic modulus, and wear resistance [1–3]. In recent years, yttria-tetragonal zirconia polycrystals (Y-TZP), with their superior combination of mechanical properties and chemical inertness, have been employed in the biomedical field as an implant material [4–9]. In general, when a restricted number of ZrO2 particles undergo the transformation during cooling from the sintering temperature, the accompanying volume expansion would cause the development of a fine distribution of microcracks in the ceramic matrix. These microcracks would increase the toughness by interacting with a propagating crack, causing deflection and blunting of the crack. Due to this nature, the engineering application of pure ZrO2 proves to be nonviable as the sintered body would crumble to pieces upon cooling from the sintering temperature [10, 11]. To overcome this undesirable phase transformation, stabilisers such as magnesia (MgO), calcia (CaO), ceria (CeO2), and yttria (Y2O3) have been added in various quantities in zirconia. In general, alloying zirconia with these oxides reduces the change of chemical
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