Advanced Materials Research Vol. 974

Abstract: This study deals with cysteine on gold (Au) nanoparticles which prepared by sodium citrate reduction. The effects of cysteine conjugated Au nanoparticles (Cys-c-Au NPs) on the microstructure and properties of the were investigated by Ultraviolet-visible spectroscopy (UV-Vis), Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), and free radical scavenging ability. The results of UV-Vis and FTIR show that the cysteine was conjugated on Au NPs surface and the conjugates were found to be stable in water. The Energy-dispersive spectrometer (EDS) result shows the typical pick of the element sulfur (S) on surface of Cys-c-Au NPs. Finally, conjugates exhibited free radical scavenging ability in presence of cysteine.

Abstract: Indium tin oxide (ITO) thin films of 150 nm thickness were deposited on quartz glass substrates by RF sputtering technique, followed by thermal annealing treatment. In this technique, the samples have been annealed at different temperature, 300OC, 400OC, 500OC respectively in Argon gas flow. Structural and surface morphological properties were analyzed by X-ray diffraction (XRD) and Atomic Force Microscopy (AFM) after annealing. The XRD showed a polycrystalline structure of ITO film with maximum peak intensity at 2θ= 30.54, <222> orientation without any change in the cubic structure. Continuous and homogeneous films obtained by the AFM after annealing treatment. The visible spectrum from the spectrophotometer showed high transparency between 81% and 95% in the. Increasing the annealing temperature yields evenly distributed pyramidal peaks shaped particles with low roughness. Resistance of ITO thin film was significantly improved from 8.75 kΩ to 1.96 kΩ after 10 minute from 300OC to 500OC annealing temperatures respectively under Argon gas flow. ITO films physical properties would be well improved by this method which is highly suitable for cost effective photonic devices.

Abstract: In recent times, the market for the applications of titanium alloys, particularly β alloys, is growing rapidly, calling for higher productivity. However, it is difficult to machine titanium alloys. A number of research activities have been carried out in this area to improve the productivity of titanium machining. Laser assisted machining is one technique which has been proposed to enhance the machinability of various difficult-to-cut materials including titanium alloys. In this study, two β titanium alloys, viz. Ti-10V-2Fe-3Al and Ti-6Cr-5Mo-5V-4Al, were machined using laser assistance and the results were compared with unassisted machining conditions. Their response to laser assisted machining in terms of differences in the cutting forces, cutting temperature and chip formation are reported. It was found that the Ti-6Cr-5Mo-5V-4Al workpiece was much more difficult to machine even with laser assistance.

Abstract: Titanium is a hard-to-machine material. An improvement in tool life via advanced tool coating materials can lead to higher productivity of titanium. In this study, a Grade 5 Ti workpiece was milled using a diamond-like carbon coated (ta-C) cutting tool and its performance compared with the standard TiAlN coated endmill. It was found that a ta-C coated tool experienced higher cutting forces than the TiAlN coated tool; however, it showed slower rate of tool wear indicating better tool life and the possibility of achieving higher metal removal rates. Hence, it was concluded that the ta-C coated cutting tool performed better than the standard TiAlN coated tool.

Abstract: How to fabricate a disposable microfluidic device is a growing interest in many application fields and micromilling is one of the efficient approaches. The benefits of using micromilling for polymer microfluidic devices include shorter fabrication process, lower cost, easier user interface, and being capable of fabricating complicated structures. The aim of this study is to use factor analysis to determine the optimal cutting conditions in micromilling microchannels on polycarbonate substrates. The parameters included spindle speed, feed rate, and the depth of cut, and the micromilled roughness was measured by a stylus profilemeter. The smallest roughness achieved was 0.127μm with the spindle speed of 20,000rpm, feed rate of 300mm/min, and the depth of cut of 10μm. From factor analysis results, the spindle speed has the largest influence while the depth of cut has the minimized impact to the surface quality of a micromilled polycarbonate substrate.

Abstract: For more than three decades, the machining industry has been employing coated tools to enhance productivity via improving tool life. Nonetheless, the problems associated with machining titanium alloys have been still prevalent. Advanced alloy materials such as diamond-like carbon (DLC) coatings are developed to combat these issues. In this study, the performance of a DLC coated tool is assessed and its tool wear mechanisms investigated. For the cutting conditions used during these trials, it has been identified that the DLC coated tool exhibited severe tool wear due to delamination and diffusion in comparison with the uncoated carbide tools. In conclusion, it is suggested that the performance of the DLC coated tools can be enhanced by applying alternate strategies to remove heat from the cutting region.

Abstract: The potential of laser assisted Direct Metal Deposition (DMD) process, for creating structures from high strength steel alloys that can be used in engineering applications requiring high strength and greater ductility in combination with high hardness is investigated. Due to increasing interest in metallic honeycomb and sandwiched structures, solid and porous specimens are prepared and examined in similar conditions. Specimen using two different powders of 316L stainless steel and H13 tool steel alloy are generated by DMD cladding on mild steel plates as substrates. The parts are tested under quasi static compressive loading and curves plotted and analysed for stress vs. strain behaviour. The results indicate that at low laser power, solid and porous steel structures with yield strength and ductility comparable to commercial grades can be produced. Porous structures show excellent characteristics suitable for applications in newly developing field of metallic honeycombs and sandwiched structures. Low modulus of elasticity is a matter of concern, but it can be improved by heat treatment.

Abstract: Cold spray (CS) is a unique spraying process where the spray materials are not melted in a spray gun. Instead, the particles are kinetically deposited on the substrate at low temperature using compressed gas. This study investigates the bonding mechanism of low pressure CS (LPCS) and high pressure CS (HPCS) techniques through smoothed particle hydrodynamics (SPH) simulations, which are achieved by modeling the single and multiple particle impacts of aluminum (Al) particles on Al substrate. The impact of Al particles on the Al substrate is analyzed by evaluating the velocity, shape, temperature of the powder particles and substrate, porosity between particles, and effect of stress on the substrate. In the case of single particle impact, HPCS results in increased particle deformation. In multiple particle impact, LPCS results in low porosity. The shape of deformation, formation of pores, and residual stress of Al can be affected by the deposition process. Results indicate that LPCS is suitable for the deposition of light materials such as Al.

Abstract: Titanium (Ti) and its alloys are widely used in medical applications due to its superior mechanical properties and biocompatibility. Hydroxyapatite (HA), due to its similarity with teeth and bone material, is also widely used in clinical applications and orthopaedic implant manufacture. In this study, composite powers containing titanium with different wt % of HA were coated on stainless steel substrate using high velocity oxy-fuel (HVOF) spray technique. These Ti+HA coatings were characterized using XRD technique to indentify phases present in the coating. Small amount of oxide phases were identified apart from the original Ti and HA in the coatings during XRD analysis. The microstructure analysis of the coating surface using FESEM and EDX revealed dense and homogeneous coatings along with few well distributed pores.

Abstract: CaCu₃Ti₄O₁₂ (CCTO) is well known to have colossal dielectric constant in the range of 10⁵.It is widely accepted that this phenomenon may be attributed to internal layer barrier capacitance (IBLC) model. The dielectric properties of CCTO were reported to be strongly dependent on the processing conditions and grain size. In this work, CCTO samples with different grain sizes were produced by varying sintering temperature in order to investigate IBLC effect on dielectric properties of CCTO. The samples were sintered at four different temperatures, (T=1100°C, 1050°C, 1000°C and 950°C). Dielectric measurements were carried out for the samples in the frequency range of 10² – 10⁶Hz using impedance spectrometer. Electron micrographs showed that increasing temperature promoted the grain growth of CCTO while sintering. The internal crystalline defects are seen to play major role by increasing the grain conductivity in dipole formation and increased the dielectric constant of the samples.