Materials Science Forum Vols. 561-565

Abstract: NiMnGa alloys are attractive for the magnetic induced shape memory effect, especially as promising functional elements in smart composite materials and structures. Recently, more attentions are put on NiMnGa composite materials. In this paper, NiMnGa particles have been dispersed and oriented in a polymer matrix with high content under magnetic field. The damping behavior of NiMnGa/polymer composites was investigated in by DMA, contrasting to the pure polymer.

Abstract: Aluminum alloys were reinforced with AlN particles using a novel chemical in situ technique. Thermodynamic analyses were made to identify the conditions for the in situ formation of the AlN in Al alloys. Experiments were conducted in the temperature range of 1173-1473 K by injecting ammonia gas. The composites with AlN quantity varying from 5 to 51 wt % were produced. Effect of process variables such as gas injection time, flow rate of ammonia gas and temperature of the alloy melt on the formation of AlN was studied. Increase in either injection time or flow rate of the ammonia gas increased the nitride content. AlN particles with an average size of 500 nm were produced. The measured Vickers hardness of the composites formed increased with increasing AlN content. The amount of AlN experimentally formed is in good agreement with the thermodynamically predicted data.

Abstract: A specimen current heating sintering process was employed to manufacture SiC particulate reinforced iron matrix composite. The results show that mechanical properties of the composite can be improved significantly with increasing pressure level, voltage, sintering time. It is found that short sintering time, fast heating and uniformly heating, surface activation of particles can be accomplished in specimen current heating hot press sintering to avoid oxidation degradation of Fe powder, and to produce fine microstructure, which contribute the main reasons for achieving higher density and higher properties. The best properties achieved so far for the composite are: density is 99.90%, Brinell hardness is 416HB and tensile strength is 838MPa.

Abstract: Hybrid inorganic-organic materials based on a polyimide (PI) and silicon dioxide (SiO2) were prepared previously only via sol-gel approach. However, sol-gel processes have some critical limitations. The primary drawback is that the resultant gel is extremely fragile and sol-gel process is complicated and costly. In this study, using SiO2 nanoparticles polyimide/SiO2 nanocomposites were synthesized from 4,4'-diaminodiphenyl ether (ODA) and 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA). A coupling agent, 3-glycidyloxyporpl trimethoxysilane (GTMOS), was used to functionalize the SiO2 nanoparticles which enhanced the compatibility between polyimide and SiO2 nanoparticles. The microstructures of polyimide/SiO2 nanocomposites were characterized by Fourier transform infrared spectroscopy (FT-IR) and wide angle X-ray diffraction (WAXD). All the polyimides show typical noncrystalline X-ray diffraction. The frequent occurrence of particular interatomic distances (R) denoted by the noncrystalline WAXD maxima were determined. All the modulus, strength and fracture strain of polyimide were improved with 5 wt% SiO2 modified with the coupling agent.

Abstract: Nacre is a natural composite material making up the inner structure of mollusk shells. It has been of great interest in materials research due to its mechanical properties far exceeding that of its individual components: well ordered plates of aragonite (a CaCO3 polymorph) within an organic polymer matrix. Generally the aragonite plates had been treated as single crystals and mechanical behavior explained as the result of micro-scale mechanisms between plates and matrix. However, recent work has shown that the plates themselves are made up of smaller nano-scale structures, which are also thought to contribute to the bulk properties. In this work, transmission electron microscopy (TEM) was used to observe the nano-scale structure of nacre from abalone. “Nanograins” of aragonite surrounded by organic material was observed, showing composite structure within aragonite plates.

Abstract: A method for measuring the stress and strain distribution in the composite materials and residual stress at the interface in the fiber reinforced composite has been developed. The strains are measured using an electron Moiré method and then the stresses are calculated from these strains. A very fine model grid with frequencies up to 10,000lines/mm can be fabricated using the optical and electron lithography techniques on the surface of the specimen and an electron beam scan which spaces are almost same as that of model grid the can be used for master-grid. The difference of the amount of secondary electrons per a primary electron makes Moiré fringes that consists bright and dark parts. Micro-creep deformation and residual strain and stress near the fibers of composite materials were measured by this method.

Abstract: Fe-B-Cr alloy powder in diameter of 32-53 μm made by argon atomization is low-pressure plasma sprayed to produce a rapidly solidified iron base composite deposit with finely dispersed boride particles. The constituents of the as-sprayed deposit formed on a water-cooled substrate are α phase and amorphous phase that are supersaturated with chromium and boron due to high cooling rate during solidification of the melt. Heat treatment of deposit at 873K leads to decomposition of the amorphous phase, resulting in the formation of Fe3B. The deposit heat treated above 1073K is composed of α phase and (Fe,Cr)2B. The as-sprayed deposit produced on a non-cooled substrate consists of α phase and (Fe,Cr)2B. The fine precipitates of about 0.1 μm in the as-sprayed deposit coated on a non-cooled substrate are boride. As deposit temperature increases, the coarsening of the precipitate particles results in lowered hardness of deposits.

Abstract: The tribological behaviour of a polymer composite is compared during small-scale and large-scale sliding tests and it is observed that test results strongly depend on the fibre orientation and test configuration. Different wear mechanisms are evaluated by optical microscopy and finite element modelling in relation to a real application of polyester/polyester discs as bearing elements.

Abstract: Vapor grown carbon fiber (VGCF) was sleaved in acetone with ultrasonic vibration. Then pure aluminum powders with 3 μm in average diameter was poured into VGCF containing acetone and mixed with ultrasonic vibration. The composites were fabricated by electro spark sintering. The strength, rigidity, electrical conductivity and microstructure of the composites was investigated. VGCF was distributed uniformly and no pores was observed in composite. As increasing the volume fraction of VGCF in composites, the strength of composites increased gradually but the elongation decreased. The electrical resistivity of the composites increased as increasing VGCF content, constantly. The theoretical resistivity of composites without residual stress is lower than that of experimental results. It seems that is caused by the high dislocation density and strain introduced by big difference of thermal expansion between VGCF and pure aluminum.

Abstract: A nano-laminar glass/metal composite was fabricated. Glass flake powder coated with silver was used as the raw material, and was sintered by hotpressing. Samples fabricated in the optimum condition had a dense, laminar microstructure originating from the aligned flake powder. The result of a three-point bending test for the samples suggested that the alignment of the powder was essential for fracture behavior: When the powder was aligned in advance during the green sample fabrication, the sample fractured stably after the maximum load, while the samples fabricated by simple hotpressing of the powder without pre-alignment fractured unstably. Work of fracture of the sample in which the powder was well aligned was measured with chevron notched specimens; a significantly high value of about 300J/mm2 was obtained.