Materials Science Forum Vols. 539-543

Abstract: The hardness and indentation fracture toughness of sub micron WC composites based on aluminide and cobalt binders were investigated. Doped Fe60Al40 and Ni3Al alloys with boron levels ranging from 0 to 0.1 wt%, were used as the aluminide binders. The composite materials were processed by uniaxial hot pressing of milled powder samples at 1500 °C under argon atmosphere. The hardness of WC-40vol%(FeAl-B) was found to be higher than that of WC-40vol%(Ni3Al-B), and it approached to the hardness level of the commercial grade of WC-10wt%Co (H10F). The fracture toughness of both WC-40vol%(FeAl-B) and WC-40vol%(Ni3Al-B) cermets was higher than that of WC-40vol%Co and the toughness increased with increasing boron content. It is believed that boron addition to the aluminide binders leads to improvement in the fracture toughness of the intermetallic matrix composites as a result of increase in the ductility and toughness of the aluminides and also due to increase in WC solubility in the aluminide binders in presence of boron.

Abstract: Embossing or imprint lithography is the key-technology for the mass production of nanosized structures with low cost. Currently Si or quartz template which is produced by e-beam or DUV lithography and reactive ion etching, is used. However they are very expensive and easily damaged due to their brittleness. On the other hand, Ni template has high mechanical durability and can be fabricated with low cost by electroplating. However, one of the key obstacles of Ni template is poor antistiction property, when it is used with sticky thermoset polymer. Due to its poor antistiction property, detachment of Ni template from epoxy substrate is one of the key obstacles. In this experiment, quartz template with 150nm to 1μm sized surface protrusion was fabricated and used to emboss the PMMA coated Si wafer. Then the imprinted PMMA layer was coated with metal seed layer and electroplating of Ni was followed to fabricate Ni template with 150nm to 1μm sized patterns. In order to form antistiction layer on Ni template, SAM antistiction layer was formed on SiO2 coated Ni template. As a result, nano patterns could be successfully transferred to sticky thermoset polymer using Ni template without any degradation of antistiction property.

Abstract: Carbon, aramid and glass fibers are inherently superior to conventional textile fibers in terms of mechanical properties as well as other chemical characteristics. Because of inherent advantages and disadvantages associated with each material, it is generally better to hybridize them to fully benefit of their high performance in many practical applications. In this paper, the possibility of hybridizing Carbon/Aramid-, Carbon/Glass- and Aramid/Glass- matrices has been investigated through the commingling process. In the experiment, several process parameters were selected and they include pressure, yarn oversupply-rate and different nozzle types. As a result of experiments, it was concluded that the hybridized materials has shown better performance than individual reinforced filament yarns in terms of mechanical properties. For small tensile forces, the Carbon/Glass/matrix combination turned out to be good enough for general purpose applications. However, for high tensile applications, Carbon/Aramid or Aramid/Glass with matrix combinations was better than the other material combinations. The hybridization process was also investigated under an air pressure of 5 bar, a yarn oversupply-rate of 1.5% for reinforced filaments, and 3.5% to 6% for matrix materials, respectively. It was also shown from the experimental results that Carbon/Glass/matrix combination may be desirable for small tensile force applications and Carbon/Aramid/matrix and Glass/Aramid/matrix combinations most suitable for heavy tensile force applications, respectively. As a matrix material, polypropylene and polyester have shown better performance than polyether-ether-keeton in terms of tensile property.

Abstract: Geo-composites are generally made by hybridizing of some components among geo-textile, geo-grid, geo-membrane, geo-net, and other materials. Due to practical applicability of geotechnical structures, the demand of geo-composites, especially for drainage application, has gradually increased. In the present study, the geo-composites bonded with geo-grid in chemical process were investigated experimentally in terms of strain evaluation and creep response values. Geo-grid plays an important role as a reinforcing material. Three kinds of geo-grid were prepared as strong yarn polyester and they were woven type, non-woven type, and wrap knitted type. The sample geo-grids were then coated with PVC. The rib tensile strength tests were conducted to evaluate geo-grid products in terms of tensile strength with regard to single rib. The test was performed according to GRI-GGI. The test results revealed that the tensile strains at the maximum tensile strength showed very good tensile deformation characteristics in the range of 10.0-13.0% in terms of mono-rib performance. Any significant trends have not found between warp knitted and woven type geo-grid in terms of the tensile strength ratios. Further experimental analysis has been conducted to investigate the wide-width strip tensile strength, contact point strength and creep features of the geo-grid samples used in this study. It was concluded again from the experiments that the tensile and creep strains of the geo-grid showed so stable values that the geo-grid prepared in this study could protect geo-textile partially in practical structure.

Abstract: AZ31 Mg alloy matrix composites were fabricated by squeeze casting method to improve high temperature properties in this study. The results showed that Mg composites reinforced with Alborex and Ag revealed improved high temperature properties and mechanical properties compared with Mg alloys. High temperature hardness and flexural strength were increased with reinforcement of Alborex, and further increase was obtained with addition of Ag. Also, Alborex reinforced AZ31 containing Ag Mg matrix composite exhibited greater improvement on creep properties. Therefore Mg composites reinforced with Alborex containing Ag were better than those reinforced with Alborex in mechanical properties and high temperature properties.

Abstract: This paper is concerned with the performance of geo-textile (GT) against chemical condition. GT is generally adopted for the upper part of geo-membrane (GM) for waste landfills and thus it is very important to consider the performance of GT against certain chemical environments until landfill is completed. In this study, PVA geo-textile/HDPE geo-membrane was prepared to investigate the waste landfill related properties in terms of long-term performance against chemical conditions imposed. GT composites of PVA GT/HDPE GM, PVA GT and HDPE GM were produced in thermal bonding process. Polyester and polypropylene GT were also manufactured in needle punching process. The experiments have been conducted under a modified version of EPA 9090 test method which is very similar to the method of evaluating chemical resistance of flexible membrane liner by the US Environmental Protection Agency (EPA). In this testing method, samples immersed in chemical of different solutions up to 150 days at 30 day interval were obtained to find tensile strength holding rate and chemical resistance. The analysis in this paper is focused to evaluate the effect of different pH conditions and temperature environments on geo-synthetics weights strength retention. It was concluded from the experiments that tensile strength of GT composites against leachate were reduced by 10 to 20% in both polypropylene and polyester non-woven GT. The reduction was more significant at temperatures of 50 °C than that at 25 °C. The experiments conducted in this study demonstrated that PVA GT is excellent in terms of chemical resistance.

Abstract: Fibers made of elements such as carbon, aramid and glass have higher mechanical properties than other conventional textile fibers and they enable the production of light weight composites as end products. Furthermore, commingling hybrid yarns generally have a characteristic feature so that their components are distributed homogeneously enough over the yarn cross section. A normal air texturerising machine was modified to produce commingling hybrid yarns for test samples. Different process parameters were applied to produce the hybridized yarn samples. However, these process parameters turned out to have little effect on the filament distribution over the hybrid yarn cross section in terms of homogeneity. The analysis in this paper is focused on the pattern of mixing of filaments over a cross section of hybrid yarns according to different combinations of reinforcement and matrix filament yarns through microscopic view. The volume content of filament in hybrid yarn cross section was maintained at 50% for both reinforced and matrix, and the hybrid yarns count at 600 tex throughout experiments. It was concluded from the experiments that the diameters of reinforcement and matrix filaments have strong effects on the pattern of mixing of filaments over a cross section of hybrid yarns such that the hybrid yarns with more or less equal diameters of reinforcement and matrix filaments showed considerably even distributions over the hybrid yarn cross section.

Abstract: Anelastic behavior of a 9Al2O3·2B2O3 (AlBw) whisker reinforced aluminum composite has been examined through the measurements of the dynamic Young’s modulus and internal friction over a temperature range of 25 to 500°C at frequencies of 0.01, 0.05 and 0.1 Hz. A standard servo-hydraulic mechanical testing machine equipped with an infrared lamp heater was employed, but the dynamic measurement system therein was especially designed by assembling a scanning laser extensometer and a frequency response analyzer for detecting the amplitude and phase lag of strain in response to a sinusoidal time-varying stress. Two peaks of internal friction were observed over the ranges 100 to 250°C (LT peak) and 250 to 400°C (HT peak), together with marked decreases in the dynamic Young's modulus in the same temperature ranges. From a quantitative analysis of the experimental data, it is concluded that the HT peak phenomenon is due to grain-boundary relaxation, whereas the LT peak phenomenon is ascribable to the relaxation caused by stress-directed interfacial diffusion of Al atoms along the whisker-matrix interface.

Abstract: Processing technique to produce open-cell porous titanium composite was developed. One of the outstanding benefits of porous titanium composite is both physical and mechanical properties can be controlled widely by changing the metal/ceramic fraction and cell structures. In this work, porous titanium composite was fabricated by a chemical reaction between titanium powder and boron carbide (B4C) powder. The reactions between titanium and B4C generates a large amount of latent heat and, therefore, it was a combustion and self-propagating mode. Precursors were made by compacting the starting powder blend (Ti and B4C), and heated in an induction furnace to induce the reaction. The reaction was strongly exothermic and, therefore, the precursor was sintered by its latent heat when the Ti/B4C blending ratio was appropriate. The reaction products were titanium boride (TiB and/or TiB2) and titanium carbide (TiC). By controlling the Ti/B4C blending ratio, it was possible to control the volume fraction of reaction products in titanium matrix. The combustion synthesized titanium composite was porous and its cell structure was strongly affected by the processing condition of the precursor (porosity and Ti/B4C blending ratio). High porosity with open pores was obtained with small Ti/B4C ratios and high porosity of the precursor, while the cell structure was closed and spherical with high Ti/B4C ratio. The cell-wall size was varied from several tens of microns to about 500 microns by changing the combustion temperature.

Abstract: Titanium carbide particle reinforced titanium composites were prepared by in-situ synthesis reaction between titanium and carbon liquid alloys. The phases constitute and microstructures of titanium composite have been investigated by OM, XRD, SEM, EPMA and TEM. Although it was possible to synthesize titanium carbide particle reinforced titanium composites, the morphology of in-situ titanium carbide grows into typically dendritic shape due to the compositional supercooling theory. The observation of TEM also show that interfaces between the reinforcements and the titanium matrix alloy are very clean.