Advanced Materials Research Vols. 264-265

Abstract: This paper discusses the microfabrication of microholes using focused ion beam and investigation of geometrical integrity of microholes. Different combination of aperture size, probe current, acceleration voltage was applied for micromachining and optimized based on taper angle. Microholes with 3.0 μm of diameter were milled according to the optimized parameter using bitmap mode. The depth range of microholes was 1.0-5.5 μm. The hole’s depth and taper angle were investigated for characterization. Each of the microholes was cross sectioned for investigation. A relationship of taper angle (θ), depth and aspect ratio were plotted. Low aspect ratio (less than 1) would give the lower taper angle and hence better integrity. Acceleration voltage of 25 kV, probe current of 41.5 pA and aperture size of 4 nm produced lower taper angle for different aspect ratio.

Abstract: This paper discusses the fabrication of nanopillars using focused ion beam (FIB) sputtering. A 25 keV Ga+ FIB was used to machine the nanopillars. A reversed bitmap method was used to fabricate nanopillars where it milled the substrate all over except the nanopillar area. The height of the nanopillars ranges from 1 to 5.5 μm with aspect ratio of 1-6. Empirical relationship of taper angle, aspect ratio and height of the nanopillar were established. Taper angle was found to be reduced as the height of the nanopillar increased. The taper angle of nanopillars depends on the acceleration voltage, probe current and dwell time.

Abstract: This article presents a quasi-steady molecular statics nanocutting simulation model for simulating orthogonal two dimension cutting copper materials with different point defects by using diamond cutters. The analyses of cutting action, cutting force, equivalent strain and equivalent stress are taken during nanocutting copper material with point defect. The two dimensional quasisteady molecular statics nanocutting model first assumes the trajectory of each atom of copper workpiece being cut whenever the diamond cutter goes forward one step. It then uses the Hooke- Jeeves search method to solve the force equilibrium equation of the Morse force in X and Y directions when each copper atom moves a small distance, so as to find the new movement position of each copper atom. Then, the displacement of the acquired new position of each atom combined with the concept of shape function of finite element method are employed to calculate the equivalent strain of the copper workpiece during nanocutting . By using the relationship equation of the flow stress-strain curve, the equivalent stress of the copper workpiece during cutting can also be calculated

Abstract: Molybdenum disiliside is known as a ceramic material with attractive properties for high temperature structural applications. In this study, mechanical alloying was used to produce MoSi2 powder directly from molybdenum oxide. Mixture of MoO3 and Si powders with commercial purity were exposed to high mechanical activation in a planetary ball mill. The ball to powder mass ratio was selected to be constant at 33:1 and the rotation speed (cup speed) was 600 rpm during the milling operations. Crystallite sizes and structural evolutions during milling were investigated by Xray diffraction analysis. The morphology of the mechanically alloyed powders was evaluated with scanning electron microscope (SEM). From XRD results, it was observed that within 6 hours of milling MoO3 was reduced and fully converted to MoO2. After 17 hours of milling MoO2 also began to reduce and peaks of MoSi2 (both
and  phases) and Mo were detected. Further milling resulted in a gradual decrease in MoO2 peak intensities because of its continuous reduction. Peaks of MoO2 were also broadened due to refinement of MoO2 crystallite sizes. Scherrer and Williamson-Hall methods using XRD patterns were employed to calculate the mean crystallite size. Calculations indicated that in the sample ball milled for 50 hours, MoSi2 crystallite sizes were less than 100 nm.

Abstract: Hydroxyapatite (HA) is considered to form major component of bones and teeth. Synthesis of hydroxyapatite (Calcium phosphate, Ca10(PO4)6(OH)2) was carried out to produce nano powders. The size and shape of nano particles was controlled during synthesis by using templates of Cetyl Trimethyl Ammonium Bromide (CTAB). A cationic surfactant, CTAB creates micellar structures which would act as nano reactors for the synthesis of nano scale HA. Yield of the final product has also been examined by varying the surfactant concentration. X-ray diffraction data revealed characteristic peaks of HA, where a predominantly hexagonal lattice structure could be deduced. FTIR was used to observe the various chemical groups present in the product. Scanning electron microscope was used for the characterization of nano particles.

Abstract: This paper reports a study of a micro-EDM process to fabricate micro-through holes in 30 micron thick copper sheets. Circular holes in various micro-sizes were produced by a micro-EDM machine and with tungsten electrodes. Scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDX) were used to identify the influence of electric sparks on the quality of the fabricated features by careful study of resulted cavitation, adhesion of debris, and re-solidification of molten materials, etc. Such analyses allow the generalization of the relevant fabrication mechanisms. In addition, measurements of overcut of the holes facilitate a working model to be developed for predicting the overcut as a function of process parameters including the discharge capacitance and the working voltage of the circuitry. Results of this study enable the derivation of proper settings for fabricating holes of good quality and permit the precision fabrication of the range of micro-throughholes.

Abstract: This paper focuses on the electrodeposition of nickel from a Ni Watts solution in the presence and absence of a permanent parallel magnetic field (PPMF) to the cathode surface. It was found that the difference between the mass deposition were enhanced in the presence of PPMF and absence of a PPMF (B = 4.4 T) with increase of current density ( m= 0.413 to 4.173 mg cm2 in 6 min). The thickness of deposited layers with PPMF was smaller than without PPMF, therefore higher density of electrodeposited layers can be brought upon by the application of PPMF. The corrosion behavior of samples was tested in the presence and absence of a PPMF (9T). The Polarization resistance was reduced in the presence of the PPMF. The deposited layers were characterized by Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Atomic force Microscopy (AFM).

Abstract: The influence of a static magnetic field of 4.4 T on the electrodeposition process on copper plates immersed in a solution of Nickel and Cobalt ions is presented. The electrodeposited layers characterized by Scanning Electron Microscopy (SEM) including Energy Dispersive X-Ray (EDX), X-Ray Diffraction (XRD) and Atomic Force Microscopy (AFM).It was observed that the difference between the mass of electrodeposition with the application of a Permanent Parallel Magnetic Field to the electrode surface (PPMF) and the electrodeposited layers without the PPMF, increased with the increase of current density. The presence of the PPMF gave smoother electrodeposited surface compared to without the PPMF. The increase in current density gave fewer the cracks on the electrodeposited surface.

Abstract: In recent years, plasma-assisted chemical vapor deposition (PACVD) has been introduced as a suitable technique to deposit hard coatings on to tools of complex geometries. This study focuses on the influence of process parameters during plasma nitriding and TiN coatings, such as duty cycle, treatment time and temperature parameters on the properties of nanostructured binary layers. To improve performance and the quality of the samples, a duplex process combining a plasma nitriding (PN) pre-treatment and a plasma-assisted chemical vapour deposition (PACVD) was applied on the steel surface. A mixture of H2, N2, Ar and TiCl4 was used to deposit a thin film of TiN on H11 steel. The microstructural, mechanical and tribological properties of the coating were investigated using X-Ray diffraction, scanning electron microscopy, atomic force microscopy combined with nanoindentation and pin-on-disc measurements. The results indicate that the small grain size was obtained at low duty cycle (33%) and increased with increasing of the duty cycle to 60 %. Calculated roughness of surface for duty cycle 50 % was 72 nm.

Abstract: In the present contribution, a 1.5kW CO2 laser in pulsed wave mode was used to study the effects of laser processing parameters at specific energy fluence. Cylindrical AISI 316L stainless steel samples rotating perpendicular to the laser irradiation direction were used for these experiments. A surface temperature prediction model was implemented to set the experimental process parameters. Laser processing of AISI 316L steel showed a strong correlation between melt pool depth and the residence time at specific fluence levels. At fixed energy fluence, increase in residence time resulted in growth of the melt pool depth. In the melted region, the microstructure was observed to be of more uniform composition and contain fewer impurities. To improve absorption level, samples were etched and roughened. These samples exhibited lower roughness levels compared to the un-treated samples. For a constant fluence level, samples with improved absorption displayed an increase in depth of melt pool at lower peak powers and higher residence time. As the laser beam interaction time increased, the surface roughness of the steel increased for the various pulse energy levels examined. While the structure of the surface was seen to retain a crystal arrangement, grain orientation changes were observed in the laser processed region.