Materials Science Forum Vols. 539-543

Abstract: To develop wear resistant nanocomposite coating materials, the authors treated nanosilica first by introducing a certain amount of grafting polymers onto the particles in terms of an irradiation technique. Through irradiation grafting, the nanoparticle agglomerates turn into a nano-composite microstructure, which in turn built up a strong interfacial interaction with the surrounding epoxy matrix during the subsequent mixing and consolidation. The experimental results indicated that the addition of the grafted nanosilica into epoxy significantly reduced wear rate and frictional coefficient of the matrix at low filler loading. Compared with the cases of microsized silica and untreated nanosilica, the employment of grafted nanosilica provided the composites with much higher tribological performance enhancement efficiency.

Abstract: Aluminium alloy composites reinforced with aluminium borate whiskers (ABw), developed recently by SHIKOKU KASEI KOUGYOU Co. Ltd., Japan, were fabricated using squeeze casting. The large mismatch in the coefficients of thermal expansion (CTE) between the reinforcement material and the matrix can generate significant stress and strain in composites during thermal cycling or during fabrication of the composites when using squeeze casting. When a transmission electron microscope is used to irradiate a very small area of a thin film of the material with a convergent electron beam of several nm in diameter, High Order Laue Zone patterns (HOLZ patterns) are obtained. These HOLZ patterns can reveal fine strain fields in the reinforcement materials that are used in composites fabricated using squeeze casting. Each (001) plane in the ABw was rotated towards the [020] direction by up to 0.5 ﾟ. With a unit of nearly 400 nm × 400 nm, each (100) plane was rotated towards the [020] direction in a corkscrew pattern. In addition the strain and the stress generated during the fabrication of the composites were estimated by using the finite element methods taking into account the anisotropies in both the CTE and the elastic modulus of the reinforcement material.

Abstract: We have synthesized multi-wall carbon nanotube (MWCNT)-reinforced Al matrix composites. The Al/MWCNT composite powders were prepared by ball milling using pristine Al or ball-milled Al powders as starting materials. The composite powders were consolidated by a conventional cold-compaction, followed by sintering. Uniform dispersion of individual MWCNTs within the matrix was in particular a critical factor for obtaining high density and high quality Al/MWCNT composites. Compared to pristine Al powders as starting materials, the Al powders previously attrition-ball-milled with carbon-based PCA (process control agent) in an ammonia atmosphere resulted in a better distribution of carbon nanotubes within the Al matrix and a higher density after sintering.

Abstract: The laminated composite of Fe–Al alloy and CrMo steel was fabricated by clad rolling to provide additional properties to the steel such as corrosion resistance, strength, and light weight. Three layered composite consisting of alloy/steel/alloy was succesfully fabricated using the process condition to satisfy the criteria for simultaneous deformation of different materials. The fabricated composite could be cold rolled to 120 μm thickness (99.8 % reduction), and wound to a coil without damage. The corrosion resistance of the composite in a sulfuric acid solution was comparable to that of monolithic CrMo steel, and it depends on the aluminium content of the Fe–Al alloy. The aluminium content dependence of the corrosion behavior is explained by the corrosion potential (Ecorr) of the Fe–Al alloy derived from the polarization curves in the solution. In order to improve the corrosion resistance of the composite, pre-oxidation treatment was conducted to form Al2O3 layer to protect the substrate. Analyses by XPS and SIMS show that the Al2O3 oxide fraction increases with the oxidization temperature and Al content of the alloy. The pre-oxidation treatment improved the corrosion resistance of the composite in a sulfuric acid solution. It is concluded that the effect of oxidation on the corrosion resistance is due to the formation of Al2O3 oxide and the Al2O3 fraction in the oxides.

Abstract: In order to estimate work of external force per unit area to infiltrate molten aluminum into bundle of two types of carbon fibers which were PAN (polyacrylonitrile) based and pitch based, wettability of graphite by molten pure aluminum and aluminum – 2.0, 2.9 and 9.1 mass % magnesium alloy was measured using sessile drop method. Basal plane and prismatic plane exist on the surface in the case of PAN and pitch based fibers, respectively. The wettability was examined in the atmosphere of Ar + 3 vol. % H2 at 1189 K. Both the contact angle and the surface tension were estimated using Young-Laplace equation. The surface tension decreased form 1.0 N/m at 0 mass % Mg to 0.7 mass % Mg at 9.1 mass % Mg. The contact angle between molten aluminum and basal plane or prismatic plane of graphite was 127º or 148º respectively. In the case of basal plane, the contact angle increased with increasing magnesium content. In the case of prismatic plane, whereas, the contact angle decreased from 155º at 2.0 mass % Mg to 125º at 2.9 mass % Mg. The work of external force for infiltration was calculated using Young’s equation. In the case of basal plane, the work was constant at 0.6 J/m2 regardless of magnesium content. In the case of prismatic plane, the work decreased with increasing magnesium content. It was found that the influence of magnesium content on the work would be different between using PAN-based carbon fiber and using pitch-based carbon fiber.

Abstract: Fabrication of nano-laminar ceramic composite by a simple sintering technique was examined. Glass flakes with a thickness of 0.7μm coated with silver were used as model materials, and were consolidated by pulsed current sintering with a uniaxial press of 7.1MPa or 30MPa. By sintering the flakes at 943K, we obtained a fairly dense composite where the flakes were aligned by uniaxial press. The silver coating remained on the flakes through the sintering, and an interface layer between the flakes was formed. The sample’s indentation test demonstrated its high resistance to crack propagation through the transverse direction of the lamellar; this result was attributed to crack deflection at the interface and the accumulation of microfractures around the indentation mark.

Abstract: A series of industry-scale and laboratory-scale W-Cu composites containing copper of 19-51 vol% were prepared by infiltrating a tungsten skeleton with liquid copper. These composites were subjected to a three-point bend test at temperatures between 77 and 363 K, and yield and maximum strengths were evaluated as a function of both the temperature and the composition. Fracture surface was observed using SEM and its fracture mode was examined. Results are summarized as follows. (1) Critical Cu content for the transition from a brittle to a ductile deformation behavior at room temperature was about 20 vol%. (2) Critical Cu content for the transition from a bcc-type to a fcc-type deformation behavior was 38-45 vol%.

Abstract: Investigations of composite materials based on EN AW-Al Cu4Mg1(A) aluminum alloy reinforced with the Ti(C,N) particles with various weight ratios of 5, 10 and 15% are presented. The metallographic examinations of composite materials show banding of the reinforcing particles in aluminum matrix after extrusion process. Structure oriented in parallel with extrusion direction is observed in composites materials. Portion of reinforcement particles Ti(C,N) has influence on the mechanical properties of composite materials. The increase of hardness, abrasive wear and decrease of compression strength, tensile strength is observed with the portion growth of reinforcement particles.