Papers by Keyword: Zirconia-Toughened Alumina (ZTA)

Abstract: This study investigates the tribological behavior of composites based on Al₂O₃–ZrO₂ stabilized with 3 mol. % Y₂O₃ (ZTA – zirconia-toughened alumina), prepared using spark plasma sintering (SPS) technology. The composites were characterized in terms of microstructure, mechanical properties, and wear resistance in a dry ball-on-flat configuration. SEM analysis confirmed a homogeneous and fine-grained microstructure without porosity, with Al₂O₃ grain sizes of 200–400 nm and ZrO₂ grain sizes of 100–200 nm. Measurements revealed high Vickers hardness (1566.7 ± 133.6 MPa), fracture toughness (6.4 ± 0.29 MPa·m¹ᐟ²), nanoindentation hardness (25.94 ± 2.35 GPa), and Young’s modulus (365.9 ± 18.2 GPa). The coefficient of friction ranged from 0.40 to 0.53 depending on the load, and the specific wear rate was extremely low (4.81 × 10⁻⁷ to 5.08 × 10⁻⁷ mm³/Nm). Analysis of the wear track revealed predominantly abrasive wear without significant fragmentation or delamination. The results demonstrate that optimized microstructure, proper phase stabilization, and a high degree of densification enable the preparation of composites with an excellent combination of hardness, toughness, and tribological resistance. These materials are suitable for demanding applications in industry, energy, and biomedicine.

Abstract: The effects of CaCO₃ and CeO₂ additions on structural, microstructural and mechanical properties of zirconia-toughened alumina (ZTA) foams were investigated. The foams were fabricated via the sponge replication technique and sintered for 4 hours. The CaCO₃ decomposition and elongated hibonite grains produced micropores. The compressive strength for both ZTA foams after adding CaCO₃ and CeO₂ was higher than the rest of the foams, respectively. The addition of CeO₂ triggered larger yttria-stabilized zirconia (YSZ) grains, which significantly improved the compressive strength of ZTA.

Abstract: The purpose of this study is to develop ZTA-MgO-MWCNT cutting insert with enhanced properties and excellent tool performance that is suitable for high-speed machining. The effects of MWCNT addition on the physical properties of ZTA-MgO composites were investigated. The samples were fabricated using 80:20 composition (80 wt.% of Al2O3: 20 wt.% of YSZ) with fixed amount of MgO at 1.1 wt.% and MWCNT ranging from (0.1 – 0.5 wt.%) as secondary additives. The CNT was pre-treated in ethanol for 1 hour using an ultrasonic homogenizer before mixing and ball milled with Al₂O₃, YSZ and MgO compositions for 24 hours. The mixture is then pressed at 100 MPa into round-shaped cutting inserts mold after being dried at 100°C for 24 hours. The pressed samples were sintered at 1600 oC for 4 hour soaking time. XRD, density, porosity and shrinkage analysis performed on the samples. The XRD analyses indicate the presence of major phases were α-Al₂O₃, ZrO₂, Zr_0.963Y_0.037O_1.982 and MgAl₂O₄. The effect of MWNT addition on density, porosity and shrinkage of ZTA-MgO shows that density (4.210 g/cm3) and percentage of shrinkage (8.05%) obtained the highest value by 0.2 wt.% MWCNT compared with samples without CNT additives which is only 4.020 g/cm3 and 7.05% respectively. High density value indicates that the shrinkage percentage is also high, which corresponds to the densification of the composites. Poor dispersion of MWCNT within the matrix is highly accounted for agglomeration around Al₂O₃ grain boundaries and decreases in densification.

Abstract: The ZTA-TiO₂-Cr₂O₃ ceramic cutting tool is a new cutting tool that possesses good hardness and fracture toughness. Yet, the performance of the ZTA-TiO₂-Cr₂O₃ cutting tool is still unknown and needs further study. In this research, the comparison of the ZTA-TiO₂-Cr₂O₃ and Kennametal ceramic cutting tool is investigated. The turning process by using ZTA-TiO₂-Cr₂O₃ and Kennametal commercial ceramic cutting tools is performed on the Bridgeport ROMI PowerPath CNC lathe machine. The parameters utilized are spindle speed in the range of 907 to 1543 rpm, feed rate from 0.08 to 0.22 mm/rev, and depth of cut of 0.2 mm. Analysis of the flank wear and crater wear were performed by using an optical microscope (NIKON MM-4001L), while the chipping area was observed by scanning electron microscopy, SEM (JEOL JSM-IT100). The surface roughness of the machined surface is measured via portable surface roughness (Mahr MarSurf M3000C). The comparison between the cutting tool produced in this research and the commercial cutting tool shows that the wear performance of the ZTA-TiO₂-Cr₂O₃ ceramic cutting tool is lower than the Kennametal commercial ceramic cutting tool. Even though this newly fabricated cutting tool is far behind compared to the commercial cutting tool, it shows some promising aspects such as the ability to cut at a higher speed.

Abstract: This study examines the effect of adding various amount of polyvinyl alcohol (PVA) from 1 wt. % to 5 wt. % as function to produce porosity of the microstructure on Zirconia-Toughened Alumina (ZTA). Porosity is required in this study which aims to increase the efficiency of carbon infiltration on the porous composite through chemical vapor infiltration (CVI). Moreover, carbon production from empty fruit bunch (EFB) was used as a reinforcement on ceramic composites in this system. The microstructure of samples was characterised by using scanning electron microscopy (SEM). The density shows the lowest at 2.864 g/cm³ when the percentage of binder is increased at 4wt.% of PVA without carbon infiltration but shows the highest density value which is 4.107 g/cm³ after carbon is infiltrated. Vickers hardness was used to identify the hardness of samples. It was found that ZTA composite with infiltrated carbon has better hardness (2053HV) with addition of 4wt.% of PVA. However, firing shrinkage showed no effect on the composite with or without carbon infiltration. The structure of crystalline carbon in composite was analyses by X-Ray Diffraction (XRD). Nevertheless, no peak for carbon is observed due to low carbon content and another alternative such as Raman spectroscopy was used to identify the presence of diffused carbon. Based on the result, carbon infiltration on composite will produce better physical and mechanical properties with the help of binders that produce pores for carbon to infiltrate.

Abstract: Ceramic composites consist of zirconia toughened alumina (ZTA) with TiO₂ as additive was fabricated via solid state sintering route. Numerous studies have indicated that TiO₂ can be used as sintering additives for Al₂O₃ and the ability of microstructural control introduce by TIO₂. The Vickers hardness of the obtained ZTA-TiO₂ was evaluated as a function of different TiO2 addition. Each sample was dry mixed, uniaxially pressed and sintered at 1600 °C for 4 hours in pressureless condition. It is noticed that the presence of TiO₂ greatly influence the microstructure of Al₂O₃. Al₂O₃ grains tend to increase in size with more addition of TiO₂. Characteristics of Vickers hardness increases increases from 1516.13 HV (0 wt% TiO₂) to 1615.8 HV (3 wt% TiO₂). Addition of TiO₂ also increases the bulk density of ZTA-TiO₂ from 3.90 g/cm³ (0 wt% TiO₂) to 4.10 g/cm³ (3 wt% TiO₂).

Abstract: In this study, ZTA powder is modified by SA with different concentrations (0wt%, 1wt%, 2wt%, 3wt%, 4wt%) for the purpose of improving its properties. The effects of SA on microstructure, particle size distribution and flowability of the ZTA powder are investigated by scanning electron microscope(SEM), laser diffraction analyzer and self-made testing device of the angle of repose. After treatment, the average diameter of the powder decreases, the powder shows better dispersibility and flowability especially when the content of SA is 3wt%. FTIR spectroscopy is employed to evaluate the effect of SA coating on ZTA powder. The results indicate that a covalent bond is formed by the reaction between the hydroxyl group of ZTA surface and carboxyl group of stearic acid. Moreover, the changing of the polarity of ZTA powder can result in a stable dispersion in organic solvents.

Abstract: Vickers hardness of zirconia toughened alumina added MgO with different composition and particle size has been studied. Five different size of magnesium oxide particle at different composition (0.5 wt % to 0.9 wt %) were used in this experiment. Each batch of composition was mixed, uniaxially pressed into 13 mm pellets and sintered at 1600oC for 4 hours in pressureless conditions. Analysis of Vickers hardness, microstructural observation and EDX analysis has been carried out. Microstructural observation showed that the addition of magnesium oxide greatly affected zirconia toughened alumina microstructure. Smaller Al2O3 grain size is observed with the presence of MgO thus improving its mechanical properties such as hardness and density. Results of Vickers hardness increased linearly with addition of more MgO until a certain composition. Each particle size of MgO addition show different composition is needed to reach the optimum Vickers hardness, depending on the particle size. The increase of hardness of the cutting insert is mainly contributed by small sized Al2O3 grains due to the microstructure pinning effect introduced by MgO. Maximum Vickers hardness achieved in this experiment is 1710 Hv, obtained at 0.7 wt% MgO with 0.15 µm particle size.

Abstract: Raman microprobe spectroscopy and atomic force microscopy (AFM) were systematically used to characterize the surface of an advanced alumina/zirconia composite (henceforth also referred to as zirconia toughened alumina, ZTA), in comparison with a commercially available femoral head made of monolithic zirconia. Experiments were conducted before and after in vitro exposure in water moist environment up to 100 h. Both materials contained zirconia partly stabilized with yttria. Tetragonal-to-monoclinic phase transformation, which was quantitatively characterized by confocal Raman spectroscopy as a function of grain size, showed significant difference between the investigated samples. Such difference was similarly found with respect to both roughness level and time needed for such topologic changes to occur. Variation of phase fractions and of topologic surface parameters were plotted as a function of in vitro exposure time and compared.

Abstract: In view of the imminent release on the Japanese market of hip prostheses made of an advanced alumina/zirconia, we performed morphologic and spectroscopic assessments of their surfaces with high spatial resolution. Femoral heads were characterized to a degree of statistical accuracy in the as-received state and after long-term exposures in vapor-moist environment. Surface and sub-surface screening was made by atomic force microscopy (AFM) and by confocal Raman spectroscopy, respectively. AFM scanning was systematically repeated with nanometer resolution on portions of surface as large as several tens of micrometers, randomly selected on the head surface, while in-depth scanning by the Raman probe allowed non-destructive analysis of phase structure in the sub-surface slab of material. Polymorphic transformation in zirconia was confined to the first few micrometers below the surface and involved no significant increase in surface roughness even after long-term environmental exposure. Surface roughness lied in a range <10 nm after environmental exposures up to 100 h, corresponding to an exposure time in vivo of several human lifetimes (i.e., according to experimentally derived thermal activation energy).