Materials Science Forum Vol. 848

Abstract: Polymer-mineral composite material is prepared by using modified epoxy resin as binder and mineral particles as aggregates. Its excellent damping characteristic and low thermal expansion make it ideal in manufacturing machine tool beds. However, the properties of this material depend on its formula and structure, so it is very important to develop an efficient method to numerically model the materials and then to optimize their properties. In this paper, 2D meso-scale finite element modeling is presented for numerical analysis of the mechanical properties of polymer-mineral composite material. The material was treated as a 2-phase composite composed of aggregates and binder which was epoxy resin mixed with fillers. Based on grading curve, the weights of aggregates were converted into the corresponding area, the aggregate particles were randomly generated and assembled with binder to produce the model. And then 2D numerical simulations were conducted under different gradations. The results show that: (1) the 2D FE model is very close to the real polymer-mineral composite material in the aspect of density and aggregate shapes and sizes, which validate the fidelity of the generated finite element model and numerical analysis method; (2) by comparing the materials’ properties under four different gradations, it can be found that the materials with SAC gradation have the best mechanical property.

Abstract: Silver nanowires–epoxy composites were prepared via cryomilling dispersion and hot-press forming process. The microstructure of the silver nanowires was studied by SEM. Dependence of dielectric properties of the composites on volume fraction of silver nanowires and frequency was investigated RF impedance material analyzer. The percolation threshold of the composites was 0.16, the value of the dielectric constant of the composite was as high as 100.

Abstract: Carbon nanotube (CNT) has been widely used as a kind of conductive inorganic filler in composites due to its excellent mechanical properties, thermal properties and electrical properties. Unfortunately, a deal of CNT is needed because it tends to agglomerate in matrix polymers. And therefore the researchers need to explore appropriate methods to decrease the usage of CNT for its high price. This paper summaries the recent development progress in carbon nanotube filled conductive polymer composites, in aspects of the approaches how to reduce the usage of CNT and application of biodegradable CNT-polymer composites. In addition, the future developing research direction in conductive polymer composites filled with carbon nanotube was indicated.

Abstract: FeSiCr-epoxy composites consisting of different FeSiCr contents were prepared through the pressure molding after mixing by cryomilling at liquid nitrogen temperature. The electromagnetic properties including ac conductivity, permittivity, and permeability were investigated in detail. The results show that the frequency dispersions of ac conductivity followed the power law, indicating the hoping conduction behavior. The real permittivity of composites increased with the increase of FeSiCr contents, and the enhancement of permittivity may be attributed to the increase of the interface area between FeSiCr and epoxy, while Debye-like dielectric relaxations were observed, and the fitting analysis of Cole-Cole curve indicates a nonideal Debye relaxation. The frequency dispersions of permeability were also relaxation linetype, which is attributed to the domain wall displacement.

Abstract: Soft magnetic material FeCoV is sensitive to magnetic field and its cost is lower than giant magnetostriction materials (Terfenol-D et al.). In the present investigation Pb (Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) with different thickness and FeCoV laminate with 0.8mm thickness were assembled into layer structure to study the effect of the PMN-PT volume fraction on the magnetoelectric coefficient of PMN-PT/FeCoV laminate composites. The ME coefficients and voltages have been characterized in the longitudinally magnetized and transversely polarized mode. The measurement was conducted under a static magnetic field superimposed with an alternating magnetic field. The influences of the static and the alternating field strength were discussed. The peak ME coefficient was obtained at 430 Oe. With the volume fraction of PMN-PT increased, the ME coefficient decreased within the experiment fraction. It can be explained by the module of M.I.Bichurin. A linear relationship was observed between the magnetoelectric voltage and the alternating field strength under a static field of 400 Oe. The ME voltage decreased when the PMN-PT volume fraction increased in the experiment fraction.

Abstract: Mullite/10 wt. %h-BN composites with 5 wt. % Y₂O₃ additive were fabricated by pressureless sintering at different temperatures. The densification, phase composition, microstructure, mechanical and dielectric properties of the mullite/h-BN composites were investigated. With the addition of Y₂O₃, the sintering temperature of the mullite/h-BN composites declined, while the density, mechanical and dielectric properties all increased. The addition of Y₂O₃ promoted the formation of liquid phase at high temperature, which accelerated the densification. Besides, Y₂O₃ particles which were located at the grain boundaries inhibited the grain growth of mullite matrix. For the mullite/h-BN composites with Y₂O₃ additive, the appropriate sintering temperature was about 1600°C. The relative density, flexural strength, fracture toughness and dielectric constant of the Y₂O₃ doped mullite/h-BN composite sintered at 1600 °C reached 82%, 135 MPa, 2.3 MPa·m^1/2 and 4.9, respectively.

Abstract: SiC nanowires were in-situ grown in SiC fiber fabrics by chemical vapor deposition (CVD) process via pyrolysis of polycarbosilane (PCS) at 1300°C and 1400°C, respectively. Then SiC_f/SiC composites were fabricated with the fabrics by polymer and infiltration pyrolysis (PIP) process. Single-filament tensile strengths of the SiC fibers heat treated at different temperature were measured. It was indicated that the mechanical property of the KD-ISiC fiber significantly degenerated above 1100°C, especially at 1400°C. Nevertheless, the prepared SiC_f/SiC composite with in-situ grown SiC nanowires exhibited good mechanical performance, suggesting that the SiC nanowire is an effective reinforcement for the SiC_f/SiC composite.

Abstract: Tantalum carbide (TaC) gradient composites were fabricated via in-situ fabrication method from the tantalum plate and gray cast iron. The morphology, phase constituents, micro-hardness, and relative abrasion resistance of the composites were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), micro-hardness tester and abrasive wear testing machine. The surface layer, which was ~160μm thick, was dense ceramic layer composed by ~90% submicron TaC particulates. The highest micro-hardness value of the dense ceramic layer was 13.84 GPa. In the sub-layer, the gradient distribution of TaC particulates reflected in the volume fraction decreased from 90% to 0%. While the micro-hardness value decreased from 10.81 GPa to 4.10 GPa. The metallurgical combination of the interface between the composites and matrix was perfect. The wear resistance of TaC reinforced iron matrix surface gradient composites increased significantly.

Abstract: In some industrial application, thermal property of resin plays an important role as same as strength. Many attempts have been made to enhance the thermal conductivity of resin matrix composite. In this paper, the copper fibers were introduced to the polyimide-based composite. The experimental results showed that the thermal conductivity of polyimide-based composite with 15% Cu fibers was as high as 8.62W/mK which is more than three times that with Cu powders. The PI-Cu composites with copper fiber had a much lower wear loss than that with copper powder. The forming of three-dimensional network by Cu fibers makes it possible that the heat can conduct by electrons in the resin-based composite with Cu fibers.