Ahmad Zahirani Ahmad Azhar

Wear performance and mechanical properties of 80 wt-%Al2O3/20 wt-%YSZ cutting inserts at different sintering rates and soaking times

Abstract A series of ceramic tools with different sintering conditions based on zirconia toughened alumina (ZTA) was produced. Experiments on ZTA cutting tools with different sintering rates and soaking times were carried out. Cutting inserts with80 wt-% alumina (Al2O3)/20 wt-% yttria stabilised zirconia (YSZ), in which Al2O3 and YSZ powders are mixed, was compacted and sintered at 1600°C using solid state sintering. Mechanical and physical properties such as wear resistance, hardness HV30, fracture toughness and microstructure were analysed. Mild steel (AISI 1018) was used as the workpiece for wear resistance study. It was observed that a slower sintering rate induces better mechanical properties on the cutting tool. With increasing the sintering rate from 2 to 8°C min−1, the wear area increased from 0·0443 to 0·118 mm2. The hardness of the samples decreased from 1563·5 to 1313·8 HV, while the fracture toughness also decreased from 4·709 to 3·95 MPa m1/2. For the effect of increasing sintering soaking time from 120 to 300 min, the wear area decreased from greatest (0·1939 mm2) to lowest (0·0797 mm2). Similarly, microstructural coarsening within ZTA was found to produce a fracture toughness increase from 3·95 to 6·374 MPa m1/2. The influence of phase polymorphic transformation on the improvement of the mechanical properties is discussed.

Fabrication of Flexible Au/ZnO/ITO/PET Memristor Using Dilute Electrodeposition Method

DRAM has been approaching its maximum physical limit due to the demand of smaller size and higher capacity memory resistor. The researchers have discovered the abilities of a memristor, a Non Volatile Memory (NVM) that could overcome the size and capacity obstacles. This paper discussed about the deposition of zinc oxide (ZnO) on indium tin oxide (ITO) coated polyethylene terephthalate (PET) substrate by electrodeposition. Metallic Zn film was deposited on substrates with varying deposition time from 15 to 120 seconds in very dilute zinc chloride (ZnCl2) aqueous and subsequently oxidized at 150 °C to form ZnO/ITO coated PET junction. The deposited thin film was characterized via x-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The results from I-V measurement show the deposited ZnO exhibits pinched hysteresis loop. The hysteresis loop becomes smaller with increasing deposition time. The 15 seconds electrodeposition gave the largest hysteresis loop and largest value of resistive switching ratio of 1.067. The result of the synthesized ZnO on the flexible substrate can be one of the alternatives to replace the current memory system as the flexible memory system.

The Effects of Cr2O3 Addition on Fracture Toughness and Phases of ZTA Ceramic Composite

Fracture toughness and phases of ceramic composites produced from alumina, yttria stabilized zirconia and chromia oxide system was investigated. The Cr2O3 weight percent was varied from 0 wt% to 1.0 wt%. Each batch of composition was mixed, uniaxially pressed 13mm diameter and sintered at 1600 C for 4 h in pressureless conditions. Studies on on their mechanical and physical properties such as Vickers hardness and fracture toughness were carried out. Results show that an addition of 0.6 wt% of Cr2O3 produces the best mechanical properties. Results of the highest fracture toughness is 4.73 MPa.m1/2,

Tetragonal and Monoclinic Phase Transformation of ZTA-MgO Ceramic Cutting Tool by Machining Process

The purpose of this study is to investigate the phase transformation route of ZTA-MgO ceramic cutting tool in raw powder form, after sintering process and after machining process. This is to evaluate the effect of phase transformation to the properties of the cutting tool i.e hardness and fracture toughness. Samples of ZTA-MgO ceramic cutting insert were fabricated by wet mixing the materials, and then dried at 100°C before crushed into powder. The powder was pressed into rhombic shape and sintered at 1600°C at 4 hours soaking time to yield dense body. To study the effect of the phase transformation of the fabricated tool, machining was performed on the stainless steel 316L at 2000 rpm cutting speed. XRD analysis were performed on three type of ZTA-MgO samples which were the raw powder, the sintered samples and also the samples after machining process. Results shows that the m-ZrO2 reduced to 0% when sintering process take place and reappear at 12% when the machining process take place proving the occurrence of transformation toughening during the machining process. The consequence of this condition is the hardness of the samples increased by 22% while the fracture toughness decreased by 21.1%.

Effect of Cr2O3-TiO2 addition on the physical properties of zirconia toughened alumina

Zirconia toughened alumina (ZTA) has good mechanical properties and widely used in cutting insert application. Although the ZTA is well known of its good mechanical properties, its still can be improved in order to produce better properties. It can be done by adding additives as reinforcement such as magnesium oxide (MgO), cerium oxide (CeO), titania (TiO2) and chromia (Cr2O3). The effect of TiO2-Cr2O3 addition on the physical properties of ZTA were investigated in this study. The composition of TiO2 was varied from 0 wt% to 3.5 wt% while Cr2O3 was fixed at 5 wt%. The starting powder materials were mixed by wet mixing for 30 minutes in acetone. Then the powder mixtures were hydraulically pressed at 260 MPa. The green pellets were sintered at 1600°C for 1 hour using an electrical furnace in presureless condition. The results were characterized by XRD, density, and also Vickers hardness. The ZTA-Cr2O3-TiO2 ceramic composite achieved the highest density of 4.1 g/cm3 and Vickers hardness of 1919 HV prior to the addition of 2.0 wt% TiO2. Therefore, it can be decisively concluded that the addition of Cr2O3-TiO2 does affected the properties of ZTA.

Thermal Conductivity of Water Based Magnetite Ferrofluids at Different Temperature for Heat Transfer Applications

Magnetic magnetite, Fe3O4 nanoparticles produced by Massart’s procedure were used to prepare water based magnetite, Fe3O4 ferrofluids without addition of any stabilizing agent or surfactant. The thermal properties and suspension stabilization of the ferrofluids were investigated by varying the magnetite, Fe3O4 nanoparticles concentration in the ferrofluids prepared. The thermal conductivity of water based ferrofluids prepared using five different volume fraction of magnetite, Fe3O4 suspension (0.1, 0.05, 0.02, 0.01 and 0.005) were measured at five different temperature, 25°C, 30°C, 40°C, 50°C and 60°C in order to evaluate its potential application as heat transfer fluid. The results shows that the thermal conductivity of the ferrofluids are higher than the base fluid, and the thermal conductivity of the ferrofluids increased as the magnetite concentration in the ferrofluids decreased however reached its optimum for ferrofluids prepared using 0.01 volume fraction of magnetite suspension over 0.99 volume fraction of water. Accordingly, the thermal conductivity of the ferrofluids significantly increased as the temperature increased where 49.4% enhancement with respect to water were observed at temperature 60°C.

The Relationship of Cutting Chip Type, Length and Thickness to Wear of Zirconia Toughened Alumina Added with Magnesium Oxide (ZTA-MgO) Cutting Tool

The effect of cutting chips on the performances of ZTA-MgO ceramic cutting tool investigated. The aim of this project is to discover the effect of cutting chip type, length and thickness on the wear of the ZTA-MgO cutting tool. CNC turning machining performed by using Rom-Bridgeport CNC turning machine at cutting speed range from 2250 to 3000 rpm, the feed rate 0.1, 0.3 and 0.5 mm/rev while the depth of cut is kept constant at 0.2 mm. The flank wear and crater wear were measured accordingly using optical microscope, Matlab programming and SEM. The chip type, length and thickness were classified and measured. The variation of cutting parameters influenced the chip geometry and it relation to tool wear were analysed. The chips were collected. The chip type, length and thickness analysed using optical microscope and SEM. Result shows chip started with tubular and ribbon form of chip. Increment of feed rate, make the chip break to smaller part. The chip length increase when cutting speed was increased. The chip is 2.49 cm length at cutting speed 2250 rpm increased up to 4.61 cm at 3000 rpm. The chip thickness was increased with increasing of feed rate where the average thickness is at lowest when the feedrate is at 0.1mm/rev and highest at 0.5 mm/rev all cutting speed. The increment of chip length caused the crater wear increased on cutting tool from 5.66 mm2 at chip length of 2.49 cm and increased to 7.40 mm2 when the length increased to 4.61 cm. The high chip thickness caused higher flank wear on the cutting tool. Based on the analysis, the chip type, length and thickness have influence on flank and crater wear of the ZTA-MgO cutting tool which may lead to failure of the cutting tool.

Effect of Calcination Temperature on the Silica Ceramic Membrane Synthesized via Sol-gel Dip-Coating Method

Ceramic membranes became one of the most important ceramic products because of their numerous benefits to many applications especially in gas separation processes. The attractive features offered by this technology include high energy efficiency, simplicity design and construction of membrane modules and environmental compatibility. The aim of this project is to get the optimum calcination temperature thus will give the optimize pore size for separation gas without cracking or pinholes the membranes. Therefore, the silica ceramic membrane was fabricated via sol-gel dip-coating method and the effect of calcination temperature on the membrane pore size was investigated. The ceramic support was dipped in the mixture solution of tetraethyl orthosilicate (TEOS), distilled water, ethyl alcohol and nitric acid with the desired molar ratio followed up by the calcination process at 400 °C, 500 °C and 600 °C. For X-ray diffraction (XRD) results, the fabricated silica ceramic membrane shows the existence of silicate hydrate when calcined at 400 °C, 500 °C and 600 °C. The XRD analysis showed the highest peak intensity at 22.5° which proved the presence of silica. From the field emission electron microscopy (FESEM) images, the pore size of the ceramic support was around 0.5 to 0.6 μm. After the silica ceramic membranes were fabricated, the pore size no longer visible under the FESEM proves that the pore size of the membranes was reduced. Fourier transform infrared spectroscopy (FTIR) showed adsorption spectra of the fabricated membranes with different calcination temperature. The broad band in the region around 1060 to 1090 cm-1 correspond to the O-Si-O bond of mesoporous silica altogether confirming the existence of silica. Based on the result analysis, the suitable calcination temperature at 500 °C with less crack and more consolidated surface membrane.

Influence of Water Molar Ratio on Fabrication of Silica Ceramic Membranes via Sol-Gel Dip-Coating Method

Ceramic membranes are an inorganic membrane that received great attention as it overcome the limitation of polymeric membrane. The silica ceramic membrane can be used in gas separation as it able to work at elevated temperature and in chemically aggressive environment. This work is conducted to study the influence of the molar ratio of water (R) on the fabrication of silica ceramic membrane by sol-gel dip-coating method. Commercial support was dipped into the solutions consist of the mixture of tetraethylorthosilicate (TEOS), distilled water and ethanol with the addition of a small amount of acid as a catalyst. The molar ratio of TEOS toethanol was fixed at 1 to 3.8 (TEOS:ethanol, 1:3.8). However, the molar ratio of water are varied at 2, 3, 4 and 4.7. FESEM (Field Emission Scanning Electron Microscope), XRD (X-ray Diffraction) and FTIR (Fourier Transform Infrared Spectroscopy) are utilized to determine the structural and chemical properties of silica ceramics that are fabricated with different R. FESEM images implied that the silica has been deposited on the surface of silica membrane and penetrate into the pore walls. XRD analysis of the fabricated silica ceramic membranes illustrated the existence of silicate hydrate. The fabricated silica ceramic membrane with silica sol molar ratio 1:3:3.8 gave the lowest intensity of XRD peak. FTIR analysis, it was observed that the presence of Si-O-Si functional group is in the range 1060 to 1080 cm-1.

Effects of TiN Single Layer Coating on the Wear of ZTA Cutting Inserts and Surface Roughness of Workpiece

Single layer TiN coated and uncoated zirconia toughened alumina (ZTA) cutting inserts were fabricated and used to machine stainless steel 316 in a turning process. The powders of alumina, yttria partially stabilized zirconia and magnesia were mixed and uniaxially pressed into rhombic cutting tool inserts and subsequently sintered at 1600°C for four hours in air. The inserts were coated with TiN layer using the PVD process. Results of wear area illustrate that the coated ZTA inserts show 66.7% increase in wear resistance compared to uncoated ZTA inserts. Commercially available Si3N4 inserts were used to compare the wear performance. Results of Si3N4 flank wear show a 64% more wear resistance compared to coated ZTA inserts. This may be attributed to the lower strength of coated ZTA cutting insert flank. Therefore, it is shown that single coating of TiN provides a significant advantage in the ZTA cutting performance and better quality surface finish.