Key Engineering Materials Vol. 908

Abstract: ZTA is considered as one of the most popular ceramic composites that are used for cutting tools due to their excellent properties. Consistent efforts should be expanded to achieve improvements in toughness and strength, and thus help them achieve a longer tool life. However, powder compaction process has been found to be a limiting factor in the production of a defect-free ceramic pellet where the green product often ruptures immediately after the compaction process or sintering process. This may be contributed by uneven distribution of pressure load, thus affecting the particles packing and properties of final product. As a solution, the present work aims to study the effect of different compaction pressure on the physical properties of ZTA-TiO₂-Cr₂O₃ ceramic composite to establish a defect-free cutting insert. The samples were fabricated by solid state processing, subjected to pressure loads varied from 200 MPa-350MPa, followed by sintering at 1600°C for 1 hour. The sintered samples were characterized accordingly. The results showed significant enhancement in density and hardness with increasing compaction pressure from 200 MPa to 300 MPa. On the other hand, further increment of pressure deteriorates the properties of the samples. These were due to the excessive external pressure which caused a very tight compaction in the mold, resulted in elastic expansion of the compact and sliding of particles as the pressure is removed. In conclusion, ZTA-TiO₂-Cr₂O₃ subjected to 300 MPa compaction pressure showed the most optimal properties with the highest density (4.58 g/cm³) and hardness (2001 HV).

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: 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: 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: In this work, the effect of low concentration of Barium (Ba) on the density, crystal structure, microstructure and dielectric properties of K_0.5Na_0.5NbO₃ (KNN) lead-free piezoelectric ceramic samples have been systematically studied. The samples were calcined at 850 °C for 6 hours and pressed using a hydraulic hand press to produce a green body disc. In this way, the green body disc of KNN was doped with 0.00 to 0.10 mol % of Ba concentration and was placed in an alumina crucible before conventional sintering at 1120 °C for 2h in air atmosphere. The increasing amount of Ba shifting all the diffraction peaks to a higher angle was measured using X-Ray Diffraction. Doping the Ba also improved the density of the KNN body. The most densified body was identified for x= 0.05 mol% of Ba which is 4.21355 g/cm³. The microstructure of the surface becomes finer and smaller after Ba doping. This shifting diffraction peaks and densified body is responsible for the enhancement of dielectric properties with the optimum value obtained from the sample doped with x= 0.05 mol%. The results show that relative permittivity (ɛ_r) was improved by the increment of Ba²⁺ concentration for 0.05 mol% which is 183.9856 for 1 kHz.

Abstract: The aim of this research is to investigate the combined effects of CeO₂ additions and hot-isostatic pressing sintering (HIPping) technique on the densification of ZTA ceramics. Addition of CeO₂ to ZTA ceramics leads to formation of a secondary phase (CeAl₁₁O₁₈) which played a vital role in affecting the density and porosity. Microstructure investigations showed that HIPping had a significant role in the removal of pores. The sample with 5 wt.% of CeO₂ addition showed the optimum value. The highest bulk density is 4.46 g/cm³ and the lowest percentage of porosity is 0.35%.

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: Four formulations of triaxial porcelain composed from 34 – 49% clay, 13 – 22% potash feldspar, 10 – 30% Soda feldspar and 14 – 28% silica sand, were prepared from raw materials sourced from Malaysian deposits. Specimens were made using the dry pressing method and characterized in terms of constituent oxide composition, compressive strength and powder-XRD analyses, respectively. XRD studies revealed that the crystalline phases are mullite and quartz and their intensity is almost identical for all samples fired at 1250°C but there is a decrease in quartz content as temperature is increased. Samples with 28% sand content resulted in higher compressive strength compared to those containing 14% and 25% sand. The major factor influencing compressive strength was found to be porosity in samples as opposed to crystallinity. A body EP3 with 64.9% SiO₂, 25.4% Al₂O₃, 3.6% K₂O, 1.5% Na₂O and 1.09% others exhibited best mechanical properties due to greater density and lower porosity formation.

Abstract: The potential of treated FGD sludge as foaming agent in ceramic porcelain were studied. The effect of treated FGD sludge content on phase composition, porosity and mechanical strength of porous ceramic were investigated. The result showed that the addition of treated FGD sludge improve the porosity. However, the increased porosity significantly reduced the flexural strength in sample after sintering at 1200°C for 3 hours. The porous of ceramic porcelain produced in this study can be used for insulation in high temperature application.

Abstract: Zinc oxide (ZnO) had been interested today because of their unique and good properties in electronic devices. ZnO nanostructured was synthesized via hydrothermal method by varied the pH value from 7, 8, 9, 10 and 11. The effect of different pH values from 7, 8, 9, 10 and 11 was changed the morphological, structure and optical properties. The samples characterized with Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD) and Ultraviolet- Visible (UV-Vis) spectroscopy. SEM is to observe the morphology images of ZnO nanostructure grains. XRD revealed the detail information on the crystallographic structure and phase formation of the materials. Lastly, UV-vis spectroscopy is to measure the band gap of optical semiconductor. From SEM result, it had shown that the hexagonal nanorods was obtained at pH 7 and pH 11 whereas nanorods is obtain at pH 8, 9 and 10. XRD revealed that the ZnO nanostructure exhibits the hexagonal wurtzite structure and the average crystallite size of ZnO nanoparticle was calculated. UV-Vis spectroscopy shows the absorption of ZnO and band determination from Tauc Plot relation plotter using UV-vis. The resulted show the pH values affect the nanostructure growth of zinc oxide semiconductor properties.