Key Engineering Materials Vols. 447-448

Abstract: This paper presents a search for Ni-Nb-Zr amorphous alloys for application as glass lens molding die materials. To efficiently screen candidate materials, we employed the combinatorial method partially to evaluate thermal stability. First, compositionally spread Ni-Nb-Zr libraries were fabricated by combinatorial arc plasma deposition (CAPD). In order to evaluate the high thermal stability, Ni-Nb-Zr amorphous samples in the libraries were annealed at 723K, the molding temperature for glass lens, for various times in vacuum. Phases in the annealed samples were identified by X-ray diffraction. From XRD identification, candidate amorphous samples with high thermal stabilities were screened. Sputtered samples with the same compositions as the candidate amorphous samples were then fabricated. Other desired properties for glass lens molding die materials, such as mechanical strength, machinability and anti-sticking properties, were evaluated. These investigations revealed Ni36Nb39Zr25 to be a suitable material for a new glass lens molding die. This material exhibited a high fracture stress f of 1.3 GPa, good heat resistance, good machinability, and excellent anti-sticking properties to molten glass.

Abstract: Composite electrolytes made of samarium-doped cerium (SDC, Ce0.8Sm0.2O1.9) and (67 mol% Li/ 33mol% Na)2CO3 carbonate salts were investigated in relation to their structure, morphology and porosity of the electrolyte. The fabrication of the SDC–(Li/Na)2CO3 composite electrolytes were achieved in two steps: step (1) preparation of the samarium-doped cerium powders by sol-gel; step (2) mixing of the samarium-doped cerium with carbonates in various compositions by solid state reaction. The electrolyte pellets were compacted at different pressures (25 and 50 MPa) and sintered at 600oC, 700oC and 800oC. The XRD results demonstrated that the introduction of carbonates did not change the SDC phase structure. FESEM images showed that the carbonate component was amorphous and well distributed in the SDC. The lowest porosity (2.92%) was achieved for samples with carbonate content of 30% (SDC7030) sintered at 800oC and cold pressed at 50MPa.

Abstract: In this paper, titanium alloy was used to prepare titanium foam using the slurry method. The compressive strength is the most important properties to be considered to produce a good sample. To achieve a high compressive strength of the titanium alloy foam, the effects of various parameters including temperature, time profile and composition have to be characterised and optimised. This paper reports the use of the Taguchi method in optimising the processing parameters of pure titanium foams. The effects of four sintering factors, namely, composition, sintering temperature, heating rate and soaking time on the compressive strength has been studied. The titanium slurry was prepared by mixing titanium alloy powder, polyethylene glycol (PEG), methylcellulose and water. Polyurethane (PU) foams were then impregnated into the slurry and later dried at room temperature. These were next sintered in a high temperature vacuum furnace. The various factors were assigned to an L9 orthogonal array. From the Analysis of Variance (ANOVA), the composition of titanium has the highest percentage of contribution (64.64) to the compressive strength followed by the soaking time of sintering factor (6.01). The optimum compressive strength was found to be 38.03 MPa for this titanium alloy foam. It was achieved with a 750% composition of titanium, sintering temperature of 1250oC, a heating rate of 1.5oC/min and 120 minutes of soaking time.

Abstract: In order to fabricate micro textured polymer plate, some kinds of ions were irradiated to the substrate by using an Electron Cyclotron Resonance (ECR) ion shower apparatus. Surface morphology of specimens was observed by SEM, and measured by AFM. We observed a lot of micro polymer brushes on the substrate. The surface roughness of untreated specimen increased and reached to 248 nm by N2 ion irradiation. We have used Argon, Nitrogen and Oxygen ions. Oxygen ion shows more effective to etch than the other two ions. Also we measured the contact angle of water on the surface of specimens with optical microscope. The contact angle of untreated specimen decreased and reached to 8 degree by N and O ion irradiation. After the irradiation, we conducted sliding friction test between ion irradiated polycarbonate slider and flat polycarbonate specimen. It was observed that friction coefficient of ion irradiated polycarbonate slider showed lower friction than flat polycarbonate specimen under mixed lubrication condition in water.

Abstract: Micro milling is an appropriate technology for the flexible production of precise micro molds with complex shapes for metal forming processes (e.g. micro deep drawing). Besides high form accuracy micro ball end milling also provides a specific surface topography which can enhance the tribological behavior during the forming processes. This paper is focusing on the tribological behavior of micro structured surfaces generated by micro milling compared to smooth surfaces. The coefficient of friction was investigated on a pin-on-disc test stand for different materials. The results of the tribological tests suggest a relationship between micro structure and coefficient of friction. Finally, the correlations between machining parameters and tribological behavior will be discussed.

Abstract: High-aspect structures are fabricated by photo-polymer elongation using a template. The template, tungsten wire of sub-mm diameter, makes SU-8 film locally stretched and deformed in long and fine fibrous geometry. The aspect ratio of fabricated structure becomes over 8, while the finest diameter is less than 10μm. Both of surface tension and viscosity of SU-8 film determines the yield of fibrous micro-structure. The wire diameter and drawing distance allow one to obtain desired profile of structure. Fibrous structures can be hexagonally aligned utilizing appropriate template with specific diameter and pitch of wire designed based on an analysis of surface energy.

Abstract: This paper discusses a design of micro-structure on the surface in contact with human from the standpoint of frictional property and feeling. Coefficient of friction on a floor varies with sliding speed in wet environment. At some condition where hydrodynamic pressure becomes dominant, the coefficient decreases and causes slip. Experiments were carried out on a special setup and structural design to decrease this pressure was discussed. It was found that structures of sub-millimeter pitch are effective in floor design. Then, the surface structure for handles was discussed. In this case, feeling becomes important rather than the change in sliding speed condition. It was found that sub-millimeter sized structure can improve the feeling while keeping high coefficient of friction under wet condition.

Abstract: Poor surface properties of magnesium alloys limit their extensive use in many applications. Laser surface engineering can be used to enhance surface-related properties of Mg alloys, and the purpose of this paper is to study the effect of laser pulse duration on surface of AZ91D Mg alloy. After millisecond-pulse laser treatment, ripples and cellular/dendrite as well as nanoscale -Mg17Al12 precipitates in the -Mg matrix were found in the surface microstructure, moreover, the melt depth was more than 150 micron. After nanosecond-pulse laser treatment, craters of 10 to 50 micron in diameter were observed on the surface due to plasma expansion and melted matter ejection during local boiling process, and the melt depth was nearly 15 micron. However, femtosecond-pulse laser treatment produced various micro- and nano-structures within a very thin layer on the surface.

Abstract: In this work, the potential of utilizing the porous alumina ceramic membrane coated with palladium as a hydrogen permselective membrane has been studied. The ceramic membrane is characterized by high permeability but at low hydrogen selectivity. In order to increase the pure hydrogen selectivity and to obtain high hydrogen yield on the ceramic membrane, palladium was coated on the alumina membrane surface. Such an arrangement would also enable the ceramic membrane to be operated at higher temperature. The preparation of the palladium coated ceramic membrane was carried out using combine sol-gel process and the electroless plating technique. The effect of combine sol-gel process with electroless plating towards deposits morphology, hydrogen permeability, and hydrogen permselectivity were analysed. The thickness and morphology of the α- Alumina and Pd composite membranes were analysed using a scanning electron microscopy (SEM) and atomic force microscopy (AFM).

Abstract: CrAlN and TiAlN coatings were deposited on stainless steel substrates by a lateral rotating cathode arc technique. The composition and structure of the as-deposited coatings were analyzed by energy dispersive analysis of X-rays (EDX) and X-ray diffraction (XRD). Thermal conductivity of these coatings is measured using pulsed photothermal reflectance (PPR) technique at room temperature. The measured thermal conductivity of pure TiN coating is around 11.9 W/mK. With increasing Al content, thermal conductivity of the TiAlN coatings decreased significantly and a minimum value of about 4.63 W/mK was obtained at the Al/Ti atomic ratio around 0.72. With the increase of Al content, thermal conductivity of CrAlN coatings decreased slightly but consistently. The variation of thermal conductivity in these coatings is explained in term of phonon scattering on grain boundaries and local strain centers caused by lattice distortion. In comparison with TiAlN, thermal conductivity of CrAlN coatings was evidently lower, which could be partially responsible for their better performance in high speed machining applications as observed in our previous work.