Sintering properties and low-temperature degradation behaviour of Y-TZP ceramics

Y-TZP ceramics has outstanding mechanical properties and has been used for many engineering applications. However, a major drawback of this ceramic is the undesirable ageing-induced tetragonal to monoclinic phase transformation resulting in properties deterioration when exposed to steam environment. In the present work, the effect of sintering temperatures (1200 to 1500°C) on mechanical properties, microstructure and low temperature ageing behaviour of the sintered Y-TZP samples were investigated. The sintered bodies were characterized to determine the bulk density, Young’s modulus, Vickers hardness and fracture toughness. The sintered samples were exposed to superheated steam at 180°C/10 bar vapor pressure and the extent of monoclinic phase development were measured at selected intervals. It was found that the relative density and Young’s modulus of the sintered samples increased with sintering temperature and attained a maximum value of 99% and 211 MPa, respectively at 1400°C. On the other hand, maximum Vickers hardness and fracture toughness of 14.4 GPa and 5.07 MPam1/2 respectively, was measured at 1350°C. X-ray diffraction studies indicated that after 24 h of ageing, no traces of monoclinic phase was found in the Y-TZP having an average grain size of below 0.3 µm. The study found that sintering at 1350-1400°C was optimum to produce sintered bodies having good ageing resistant without sacrificing the mechanical properties

Low-temperature degradation and defect relationship in yttria-tetragonal zirconia polycrystal ceramic

In this work, the relationship between tetragonal to monoclinic phase transformation and photoluminescence spectrum were studied for 3 mol% yttria-tetragonal zirconia polycrystal samples sintered in air and argon atmosphere at 1500 degrees C. A low-temperature degradation study was conducted under autoclave conditions containing superheated steam at 180 degrees C and 10 bar vapour pressure for periods up to 12 hours. Photoluminescence studies were conducted using a photoluminescence spectroscope with helium-cadmium laser at a wavelength of 325 nm as the excitation source, and the phase content in the zirconia samples was measured using X-ray diffractometer. The studies concluded that argon gas sintered samples have higher structural vacancy than air sintered samples; the argon gas sintered sample showed a more rapid phase transformation than the air sintered sample and also showed that the defect associated with oxygen vacancies in the zirconia lattice increases with increasing aging time

Sintering behaviour and properties of manganese-doped alumina

The effect of manganese (0.1, 0.5 and 1.0 wt%) on the sintering and mechanical properties of alumina was studied. Sintering was carried out by the conventional heating method in a box furnace and in a hybrid multimode microwave furnace. XRD analysis revealed the precipitation of a spinel second phase (MnAl 2 O 4 ) in manganese-doped samples as a result of manganese limited solubility in the corundum lattice. The addition of 0.1 wt% manganese was most beneficial in enhancing the densification of alumina (97.5% relative density when compared to 94.2% for the undoped sample), hindered grain growth, and improved the hardness of the ceramic when sintered at 1500 C. The study also revealed that microwave sintering was effective in suppressing grain growth of alumina. In addition, the hardness was dependent on the sintered bulk density and that grain coarsening ensued as the density of the sintered alumina exceeded 95% of theoretical.The authors gratefully acknowledge University of Malaya , Malaysia for the support rendered in carrying out this research.Scopu

Effect of sintering holding time on low-temperature degradation of yttria stabilised zirconia ceramics

Effect of sintering holding time on low-temperature degradation of 3 mol-% yttria stabilised zirconia was investigated. Yttria stabilised zirconia samples were sintered using a two-step sintering cycle. The samples were initially heated to 1500°C with the heating rate of 10°C min−1, held for 1 minute before cooling down to 1200°C and kept at this temperature for varying holding times from 0 to 10 hours. The phase contents of the zirconia samples were measured using X-ray diffractometer, and the microstructural evaluation was evaluated by field emission scanning electron microscope. All the as-sintered samples exhibited 100% tetragonal phase and bulk density of about 6 g cm−3. The low-temperature degradation study was conducted under autoclave condition containing superheated steam at 180°C and 10 bar vapour pressure for periods up to 24 hours. The results showed that the tetragonal to monoclinic phase transformation decreased with increasing holding time up to 3 hours and thereafter it increased. The sample sintered with 3-hour holding time showed better aging resistance than other samples. It was found that the grain size of this sample was the lowest (0·29 μm) when compared to other samples

Effect of microwave sintering on the properties of copper oxide doped Y-TZP ceramics

The effect of various amounts of copper oxide (CuO) up to 1 wt% on the densification behaviour and mechanical properties of 3 mol% yttria-tetragonal zirconia polycrystal (Y-TZP) were studied by using microwave (MW) sintering method. The MW sintering was performed at temperatures between 1100 ?C and 1400 ?C, with a heating rate of 30 ?C/min. and holding time of 5 min. The beneficial effect of MW in enhancing densification was also compared for the undoped and 0.2 wt% CuO-doped Y-TZP when subjected to conventional sintering (CS) method. The results showed that significant enhancement in the relative density and Vickers hardness were observed for the undoped Y-TZP when MW-sintered between 1100 ?C and 1250 ?C. It was revealed that the 0.2 wt% CuO-doped Y-TZP and MW sintered at 1250?1300 ?C could attain ? 99.8% of theoretical density, Vickers hardness of about 14.4 GPa, fracture toughness of 7.8 MPam1/2 and exhibited fine equiaxed tetragonal grain size of below 0.25 ?m. In contrast, the addition of 1 wt% CuO was detrimental and the samples exhibited about 50% monoclinic phase upon sintering coupled with poor bulk density and mechanical properties. The study also revealed that the addition of 0.2 wt% CuO and subjected to conventional sintering produced similar densification as that obtained for microwave sintering, thus indicating that the dopant played a more significant role than the sintering method.The authors thank University of Malaya for the financial support (PPP Grant No. PG091-2015A ) in carrying out this research.Scopu

Effect of microwave sintering on the properties of copper oxide doped Y-TZP ceramics

The effect of various amounts of copper oxide (CuO) up to 1 wt% on the densification behaviour and mechanical properties of 3 mol% yttria-tetragonal zirconia polycrystal (Y-TZP) were studied by using microwave (MW) sintering method. The MW sintering was performed at temperatures between 1100 °C and 1400 °C, with a heating rate of 30 °C/min. and holding time of 5 min. The beneficial effect of MW in enhancing densification was also compared for the undoped and 0.2 wt% CuO-doped Y-TZP when subjected to conventional sintering (CS) method. The results showed that significant enhancement in the relative density and Vickers hardness were observed for the undoped Y-TZP when MW-sintered between 1100 °C and 1250 °C. It was revealed that the 0.2 wt% CuO-doped Y-TZP and MW sintered at 1250–1300 °C could attain ≥ 99.8% of theoretical density, Vickers hardness of about 14.4 GPa, fracture toughness of 7.8 MPam1/2 and exhibited fine equiaxed tetragonal grain size of below 0.25 µm. In contrast, the addition of 1 wt% CuO was detrimental and the samples exhibited about 50% monoclinic phase upon sintering coupled with poor bulk density and mechanical properties. The study also revealed that the addition of 0.2 wt% CuO and subjected to conventional sintering produced similar densification as that obtained for microwave sintering, thus indicating that the dopant played a more significant role than the sintering method