Advanced Materials Research Vols. 123-125

Abstract: WC-Cr3C2 cermet coating on carbon steel was fabricated by laser controlled reactive synthesis and exhibited the metallurgical bonding at the interface between coating and substrate. Experimental results show that addition of Ni results in a significant change on phases and microstructure of coating. Ni addition remarkable improves resistance to thermal shock of coating. This is accounted for by increasing planar crystal zone of the coating due to Ni addition, which decreases stress concentration at the interface.

Abstract: Delamination failure occurs due to the out-of-plane loading because of the weakness in the thickness directional properties of composite materials. The z-pinned composite has been developed to overcome such a problem. In this study, the mechanical properties of z-pinned composite laminates were examined using the analytical model. The effects of z-pins on the strength in the thickness direction were investigated. Fibers in the laminate are gradually waved by the formation of resin rich zone caused by inserting the z-pins. A constitutive model was developed for the predictions of strengths of woven z-pinned composites. The changes in the strengths in the in-plane and out-of-plane directions of the woven z-pinned composites and the effects of controlling parameters such as the diameter of z-pin and densities of z-pin on the strengths were identified. It was found that the out-of-plane tensile strength increases 14% relative to that of composite without z-pins when the diameter of z-pin is 0.25 mm. However, the in-plane tensile strength and in-plane and out-of-plane shear strengths were reduced to 9%, 7% and 8%, respectively, over the strengths of composite without z-pins. Qualitatively good correlations are obtained between the results of the suggested model and the experiments.

Abstract: Al-Cu-Mg alloy and its matrix composites reinforced with different volume fractions of sub-micron silicon carbide particles have been produced in powder metallurgy route. The effects of silicon carbon particles and mechanical alloying (MA) technology on the mechanical and tribological properties were investigated. The results show that the composites have better mechanical and tribological properties than the matrix alloy, and the 9vol%SiCp/Al-Cu-Mg composite has the best performances. Mechanical alloying (MA) technology further improves the hardness and tensile strength, hardly influences the wear rate of the 9vol%SiCp/Al-Cu-Mg composite but somewhat affects its friction coefficient.

Abstract: Montmorillonite (MMT) was modified by octadecylamine (ODA) surfactant. The surfactant contents were varied, i.e. 0.5, 1.0 and 2.0 times the cation exchange capacity (CEC) of the MMT. XRD and FTIR spectra of the organoclay revealed that ODA molecules intercalated into MMT layers. The MMT-ODA was melt-mixed with natural rubber (NR) using a two roll mill. Effects of surfactant content and organoclay content on cure characteristics, mechanical properties, and morphologies of NR nanocomposites were investigated. Morphologies of the NR nanocomposites, with increasing surfactant content, revealed the exfoliated structure and the good dispersion of the organoclay in the NR matrix. These caused the enhancement of mechanical properties of the NR nanocomposites. With increasing the MMT-ODA2 content up to 5 phr, scorch time and cure time of the NR nanocomposites decreased while their tensile strength increased.

Abstract: The present study investigates the effect of the carboxylated multi-walled carbon nanotube (0~3 wt %) content on the electrical and thermal properties of high density polyethylene/carbon black/carboxylated multi-walled carbon nanotube (HDPE/CB/c-MWNT) hybrid nanocomposites. The room temperature electrical resistivity and positive temperature coefficient (PTC) intensity of the nanocomposites significantly improved with the addition of c-MWNT. However, the heat of fusion decreases as the amount of c-MWNT increases. Further, the microstructural parameters such as the fractional free volume (Fv) and free volume hole size (Vf) of the nanocomposites shows appreciable changes around the percolation threshold. Secondly, the PALS results seem to correlate well with the electrical and thermal properties of the composites.

Abstract: Electromagnetic shielding effect material is needed because electronic devices suffer electromagnetic interference. Otherwise, in many engineering designs such as antenna fairings, sonar cover and stealth aircraft, materials with good electromagnetic penetration are desired. High performance fiber-reinforced composites have high specific strength and mechanical properties, and there is therefore a need to develop an electronics enclosure with optimum shielding by using a combination of particular fiber reinforcements and a polymer matrix. This paper describes the development of high-performance fiber-reinforced composites that use four high strength fibers (super fibers), Dyneema SK60 (an ultra-high molecular weight polyethylene fiber), Zylon HM (poly-p-phenylenebenzobisoxazole fiber), Technora T-241J (aramid fiber) and Torayca T800HB (carbon fiber). These super fibers were fabricated by compression molding and their shielding effectiveness (SE) was tested. The results showed that the newly developed Dyneema fiber, Zylon fiber and Technora fiber composites exhibited low electromagnetic shielding properties of 1.3~2.3 dB at a frequency of 0.5~18 GHz. Furthermore, the Torayca fiber composite has high electromagnetic shielding properties of 10.2~20.7 dB at the same frequency. It is expected that these high-strength composites with optimum SE can be obtained by controlling the electromagnetic shielding properties from hybrid multi-fiber structures.

Abstract: The composites of mechanical and thermal properties of modified and unmodified Carbon nanotube /epoxy resin nanocomposites tested under various circumstances is a major investigation in this study. Identification of functional groups of CNT surface using Fourier transforms infrared spectroscopy (FTIR) was done to male sure if the means of modification adopted in this study is successfully. The tensile and flexural strengths of modified CNT-containing nanocomposites with the amount of modified CNT around 0.75 Phr tested under room temperature circumstance increase 10.96 % and 21.44 % respectively. These two strengths of nanocomposites tested under high temperature circumstance increase 14.55 % and 10.80 % respectively. Additionally, both strengths of nanocomposites tested under high temp.-high humidity circumstance increase 11.65 % and 23.53 % respectively. According to the test results using pyris diamond thermomechanical analyzer (TMA) coefficient decreases 39.81 % with increasing the content of modified CNT and meanwhile glass transition temperature increases 4.15 %. Because of above-mentioned effect, a modified CNs-containing nanocomposite possesses great thermo stability. Overall, No matter what circumstance (high temperature or high temp.-high humidity circumstances) nanocomposites expose to, and no matter whether CNT are modified or not, CNT do significantly enhance mechanical and physical properties of composite.

Abstract: In recent year, the environmental consciousness is awakening; hence, the plastic recycling and reusing techniques have drawn much attention. In this paper, impact-resistant polypropylene(IRPP) chips were mixed with nano far-infrared master batches polypropylene(NFMPP) chips in different weight ratios. Then the polypropylene composite plates were formed by using a single screw extruder. Afterward, this study also simulated the plastics recycling procedure from 1 to 6 times, respectively. The results shown the average far-infrared emissivity of polypropylene composite plates were 0.90±0.02ε. In the IZOD measurement, the impact strength of polypropylene composite plate which processed for six times dropped by 20% comparing to the composite plate processed only once.

Abstract: In this paper, the 1-3-2 piezoelectric composites were fabricated by the cut-filling technique using P(MN)ZT piezoelectric ceramic as functional materials and polymer as matrix. The effects of ceramic volume fraction on the electrical properties of the composites were studied. The results indicate that as the ceramic volume fraction increases, the piezoelectric stain factor d33 increases evidently, while the piezoelectric voltage factor g33 decreases. Besides, the planar electromechanical coupling factor Kp and mechanical quality factor Qm of the composite are also less than those of the pure ceramic, while the thickness electromechanical coupling factor Kt is larger than that of the ceramic.

Abstract: Composites with compositions La0.7Ca0.3MnO3(LCMO) and La0.7Sr0.3MnO3(LSMO)/SnO2 were prepared by a standard ceramic technique. The structure and morphology of the composites have been studied by the X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The XRD and SEM results indicate that no reaction occurs between La based maganite and SnO2 grains, and that SnO2 segregates mostly at the grain boundaries of La based maganite. The variation in resistivity with temperature has been studied and shows a semiconducting behavior, furthermore the composites exhibit metallic percolation. It is interesting to note that an enhanced magnetoresisitance (MR) effect for the composites is found over a wide temperature range from low temperature to room temperature in an applied magnetic field of 0.5 Tesla. The spin-polarized tunneling and the spin-polarized tunneling may be attributed to the enhanced low-field magnetoresistance (LFMR) effect.