Materials Science Forum Vols. 783-786

Abstract: Careful consideration of friction and wear could save the U.S. economy as much as $120 billion per year. Friction, wear, and lubrication have direct influence on the performance, reliability, and service life of a device that contains moving components. These components are found in applications of energy conversion, power generation, energy harvesting in the broader fields such as agriculture, transportation, and bioengineering etc. The useful life of these systems and their energy efficiency can further be improved by improving the surface performances of sliding systems. Ceramics matrix multifunctional composite due to their unique properties are one of the alternatives for these applications. We report development of alumina based ceramic matrix composites (CMCs) with in-situ functional phases. The overview of properties will be provided. The mechanism for low friction will be discussed. In this investigation, the reinforcement (boron) addition showed strong influence on the in-situ phase formation and surface performance. The phase characterization confirmed formation of AlB₂, B₂O₃, and Al₁₈B₄O₃₃. The sintering temperature showed influence on the stability of these phases. The mixed mode failure was evident from the wear tests. It was found that the coefficient of friction was reduced up to 30% when compared to parent alumina. These newly designed multifunctional composites potential candidate materials that improve the energy efficiency and sustainability.

Abstract: Wear behaviour of AE42 Mg alloy-based composites reinforced with Saffil short fibres (SSF) and SiC particles (SiC_p) in various combinations has been investigated in transverse direction, i.e., the plane containing random fibre-orientation was parallel to the steel counter-face. Wear tests are conducted on a pin-on-disc set-up under dry sliding condition having a constant sliding velocity of 0.837 m/s for a constant sliding distance of 2.5 km in the load range of 10-40 N. It is observed that the hybrid composites reinforced with both SSF and SiC_p exhibit better wear resistance than the composite reinforced with SSF alone, because SiC_p are harder than SSF and remain intact retaining their load bearing capacity even at the highest load employed in the present investigation. The dominant wear mechanism is observed to be abrasion for all the composites. It is accompanied by fracture and pull-out of SSF from the worn surfaces. Wear behaviour of the composites in transverse direction is also compared with wear behaviour in longitudinal direction, i.e., the plane containing random fibre-orientation was perpendicular to the steel counter-face, reported earlier by the same authors. It is observed that the wear resistance of the composites in transverse direction is lower than that in longitudinal direction due to the lower load bearing capacity, the extensive fracture and pull-out of SSF from the worn surfaces.

Abstract: The effect of Cu-Sn coating on steel towards improving the adhesion between steel and typical styrene butadiene rubber (SBR) based tyre bead composition has been investigated in this work. Steel coupons were coated with varying compositions of Cu-Sn via immersion coating, where the electrolyte bath composition was varied. Chemical analysis of the coatings using ICP-OES confirmed increase in Sn content with increasing SnSO₄ concentration in the coating baths, keeping other parameters constant. No change in the coating weight was observed with change in Sn concentration in the coatings. Bare spots on the coating surface was observed under SEM XPS analysis confirmed formation of Fe oxide at the bare locations. The coated steel plates were vulcanized with SBR based rubber and peel strength was measured. The results confirmed an optimum Sn concentration of 3 - 4 wt% in the coatings up to which an increase (~ 25%) in adhesion strength was exhibited compared to only Cu coatings. Stereo-microscopic analysis of the peel tested samples validated mixed mode i.e. both adhesive and cohesive modes of failure.

Abstract: Multiwalled carbon nanotube (MWCNT) reinforced Al-Si (11 wt%) alloy based nanocomposites were synthesized by spark plasma sintering using high energy ball milled nanocrystalline Al-Si powders mixed with physically functionalized MWCNTs. Improvement in MWCNT dispersion and associated improvement in densification of the nanocomposites were confirmed. The microhardness and elastic modulus of the nanocomposites measured by nanoindentation exhibited appreciable improvement. Grain size measurement by X ray diffraction and transmission electron microscopy confirmed achievement of nanocrystalline grains in Al-Si powder after ball milling, as well as in the consolidated nanocomposites. TEM analysis was performed to reveal the dislocation activity, effect of presence of primary Si and distribution of MWCNTs in the nanocomposites.

Abstract: Nanocrystalline composite powders were prepared by mechanical alloying of pure Cu, Fe and Co as metallic major part and Al₂O₃ or Fe₂O₃ or SiO₂ as ceramic reinforcement in a high-energy ball mill. Alloys of the copper-iron-cobalt system are promising for the development of new materials and applications. Cu-Fe-Co is used in different applications depending on the properties required. These can be related for example to toughness when used as rock cutting tool, to magnetic and electric properties for microelectronics or to chemical behaviour when used as catalysts in bioalcohol production industry. The objective of the present study is to contribute to understanding how and to which amount the ceramic reinforcement affects the properties for which this Cu-Fe-Co system is used as well as to envisage other less frequently uses for the composite powders. Structural and magnetic transformations occurring in the material during milling were studied with the use of X-ray diffraction, scanning quantum induction device (SQUID) and magnetic force microscopy (MFM). In mechanical alloying the transformations depend upon milling time. The results showed that milling the elemental powders of Cu-Fe-Co in the mass proportion of 50:25:25 respectively for times up to 10h leads to the progressive dissolution of Fe and Co atoms into FCC Cu and the final product of the MA process was the nanocrystalline Cu containing Fe and Co with a mean crystallite size (from coherent crystal size determination by diffraction) of 20 nm aprox. When ceramic particles are milled together with the metals (at proportions of the oxides between 1-10%) this mechanism is retarded. On the other hand, the lowest mean crystallite size is reached without ceramic particles in the milling process. However the composite powder produced in all the cases stabilized similar lowest crystallite size between 45-50 nm. Mechanically alloyed metallic-ceramic composite powder showed lower saturation magnetization than the metallic system but enhanced coercive field (significantly for hematite reinforcement). All the studied systems are intermediate ferromagnetics (H_c≈104 A/m). Milling time significantly affects the structure, composition and properties for both metallic and composite systems.

Abstract: T wisted yarns are used for bio-composites and nanocomposites as reinforcement . In a twisted yarn, single yarns migrate from surface to inner along the yarn axis. In this research , migration structure is studied by using X-ray CT system . The result is obtained that the orientation angle correlates with layer .

Abstract: Many of the advanced composite materials used in aerospace, energy storage and conversion, and electrical devices are multifunctional, i.e., they operate on (or in the presence of) some combination of mechanical, thermal, electrical, chemical, and magnetic fields. Designing composite materials for airplanes, for example, must include not only structural, but also thermal and electrical considerations. Most energy storage and conversion devices are made from advanced composite materials, and they must be designed to interact and sustain their functions in multiple fields, often mechanical, electrical, electrochemical, and thermal. The functional characteristics of such materials are not only controlled by the constituent properties, but are highly dependent on the size, shape, geometry, arrangement, and interfaces between the constituent materials, the extrinsic factors controlled by processing. That is the subject of the present paper. In particular, we will focus on the design of microstructure in heterogeneous materials to manage the dielectric properties and character of such materials.

Abstract: The present study aims at producing Al-based nanocomposites reinforced with low fractions of ceramic nanoreinforcement produced by thermal plasma, evaluating the strengthening effects induced by their addition to the widely used A356 (Al-Si-Mg) cast aluminum alloy. Nanoparticles were produced using a lab-scale RF inductively coupled thermal plasma system designed by simulation as to optimize the plasma operating conditions and reactor geometry. During the casting route, ultrasonic treatment of the melt was performed to better disperse the reinforcing particles into the matrix. Ceramic spherodized microparticles were also synthesized and micro-reinforced Al-matrix composites were produced with the same route for comparison. Microstructural characterization of the cast samples was carried out by optical and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) analysis. BET analysis was also used for powder characterization. Hardness tests were performed to assess the enhancement in mechanical properties obtained by addition of nanoparticles with respect to both the microparticle reinforced and unreinforced Al-Si-Mg matrix.

Abstract: 20vol% TiB₂ particle Al composites were fabricated by spark plasma sintering after blending TiB₂ and Al particles. The dispersibility of TiB₂ particles in composites was controlled by the blending method before sintering. Then the effect of the dispersibility on the electrical conductivity was estimated. As increasing the dispersibility, the electrical conductivity of the composites decreased. The dispersibility of TiB₂ particles in composites was estimated by two-dimensional local number (LN2D), quantitatively. The theoretical value of electrical conductivity considering LN2D was estimated by the simulation of finite volume method and the Laplace equation of electric potential distribution. The tendency of low electrical conductivity of the composite with uniform distribution of TiB₂ particles was confirmed by this simulation, but the experimental degradation of electrical conductivity for uniform distribution for clustering distribution was higher than that of theoretical value. The electrical conductivity of Al seems to be affected by the plastic deformation. There are the deformation regions around the interface between TiB₂ particle and Al because of the difference of thermal expansion. Therefore, the quantity of the deformation region is increasing for increasing the dispersibility, and then the electrical conductivity of the composites decrease.

Abstract: Reduction of frictional coefficient at sliding position can improve wear resistance of material. In previous studies, Cu-based composites containing graphite particles have been reported. Since graphite is better lubrication material, the Cu-based composites containing graphite particles have better wear property comparing with the pure Cu. However, these composites are mainly fabricated by sintering method and its strength is relatively low. In this study, Cu-based composites containing graphite particles are fabricated by centrifugal mixed-powder casting. The centrifugal mixed-powder casting is novel centrifugal casting method combined with powder metallurgy. Using this casting method, the Cu-based composites containing graphite particles are successfully obtained. The graphite particles are distributed in the Cu matrix and no casting defects are observed. Moreover, wear resistance of these Cu-based composites are much better than pure Cu, and the frictional coefficient between these composites and bearing steel as the counter part is reduced by dispersion of the graphite particles. Furthermore, it is found that the optimum area fraction of the graphite particles to improve the wear resistance of the present Cu-based composite is from 15% to 21%.