Materials Science Forum Vols. 546-549

Abstract: A low temperature cure resin has been prepared successfully by applying self designed/synthesized cure agent and commercial epoxies through slurry mixing process. Low temperature/vacuum bag cure prepreg with excellent drapeability & spreadability and over 10 days storage life at room temperature could be prepared by hot/melt technique. The cure and post cure parameters of manufacturing composites were optimized. The main properties of low temperature/vacuum bag cure composite have been determined. Results indicated that the low temperature/vacuum bag cure composite system had excellent mechanical properties and its long service temperature could reach 80°C. The influence of ultrasonic irradiation applied during the manufacturing process on the properties of the composite was discussed, and results showed that the ultrasonic irradiation improved the properties of composite greatly and suggested a novel strategy to improve the mechanical properties of low temperature cure composite systems.

Abstract: The Ti6Al4V composites reinforced with Chinese SiC fiber was manufactured and then thermally exposed at 800°C, 900°C and 1000°C, respectively, for up to 500h. The interfacial reaction products were identified as TiC between Ti6Al4V and the C-coating of the SiC fiber. However, if the SiC fiber has no C-coating, the interfacial reaction forms TiC, Ti3SiC2, Ti5Si3(Cx) and Ti3Si(Cx). The thickness of the interfacial reaction zone was measured and it is found that the thickening rate is slower in the samples in which the SiC fiber has the C-coating. The growth of the interfacial reaction products is diffusion-controlled and the parameters of the growth kinetics, k0 and Q, were determined, respectively. The profile of the element distribution was calculated according to the diffusion theory and is well consistent with the expeimental data.

Abstract: Steel-bonded cemented carbide GT35 was fabricated from natural ilmenite by in-situ carbothermic reduction and vacuum pressureless sintering. The effects of Mo-doped on the mechanical properties and microstructures of GT35 composites were investigated. That the good mechanical properties of steel-bonded cemented carbide GT35 with 9wt% Mo were obtained at the same sintering condition that the density reached 6.223g/cm3 and the average bending strength reached about 1155.6MPa after heat treatment, but the hardness dropped the lowest value HRC 60.94 and the difference was not apparent with the change of Mo content. The additive of Mo is beneficial to be refinement of carbide particle size, sphericity of grains and formation of compact composite. In-situ reduction of natural ilmenite was a feasible way to fabricate good performance composite GT35 with a relative low cost.

Abstract: The objective of present work is to investigate the internal friction behavior of TiNi shape memory alloy fiber/Ni matrix composite. The TiNi fiber/Ni matrix composite was fabricated by an electroplating method using TiNi alloy fiber as the cathode and Ni plate as the anode. The internal friction as functions of temperature and strain amplitude was measured respectively. The results showed that the internal friction peaks of the TiNi/Ni matrix composites, which due to the martensitic reverse transformation of the TiNi fiber, broadened with increasing prestrain level. There was a sharp internal friction increment at the high temperature, which due to thermal expansion mismatch between the TiNi fiber and Ni matrix and recovery stress generated. Contrast to the pure TiNi alloys, the internal friction background of the TiNi/Ni composites increased with increasing temperature. Furthermore, the internal friction of the TiNi/Ni composites decreased with increasing strain amplitude measured.

Abstract: The chemical element and its valence at the fracture surface of SiCp/Al2O3-Al composites synthesized by oxidative infiltration of Al melt were analyzed quantitatively using X-ray photoelectron spectrometer(XPS), the percentage content of various phase at fracture surface was determined accordingly. Additionally, the volume fraction of different phase in the composites was meassured by optical metallographic examination of the three-dimensional section. And then, by the comparison of phase content between fracture surface and section of the composites, the preference for the crack penetrating various phases of the composites was identified ,which in turn micro-fracture mechanisms of the composites were revealed quantitatively. It is proved that SiC particle size has a critical influence on the percent content of co-continuous Al2O3 and Al phases, as well as the micro-fracture mechanisms of this kind of composites. Based on the analysis of micro-fracture mechanisms, the moderate size (about 10μm) of SiC particulate would be beneficial to the mechanical properties of composites, the tested results of mechanical properties under room and elevated temperature verified the hypothesis.

Abstract: Smart composite material-MRF’s rheological properties such as viscosity and shear modulus can vary when subjected to different magnetic fields. This paper established the vibration model of the smart composite beam featuring MRF. The vibration analysis was finished under different magnetic field strengths using the method of complex stiffness. The experiment was performed to validate the theoretical predicted vibration responses. From both studies, the natural frequencies and loss factors of the MRF beam were shifted to a higher lever when the applied magnetic field increases. From the findings of the analysis, it is observed that MRF presents vibration control capabilities.

Abstract: Aluminum matrix composites, reinforced by 0.15μm and 5μm Al2O3 particles with 40% volume fractions were fabricated by squeeze casting technique. The microstructure characterization near the interfaces of Al2O3p/1070Al composites was investigated by SADP and HREM techniques. Results showed that high-density dislocations were generated in the 5μm-Al2O3p/Al composite due to the thermal mismatch stress. In contrast, the matrix of the 0.15μm-Al2O3p/Al composite appeared to be nearly free dislocations and some “micro distortion areas” of 1-5nm were observed, which was attributed to the dispersion of fine sub-micron particles and uniform distribution of the stress near the interfaces.

Abstract: Csf/Si3N4 composites were prepared by hot-press sintering method using α-Si3N4 power, short chopping carbon-fiber and sintering additives. XRD analysis showed that the α-Si3N4 was almost completely transferred into β-Si3N4. The SEM micrographs of fractured surfaces showed that special network developed by rod-like β- Si3N4 grains. The flexure strength of 590±10MPa, and fracture toughness of 7.94±0.1MPa·m1/2 were achieved for the samples incorporated with 0.5wt% the carbon fibers .The microwave dielectric property of Csf/Si3N4 composites was measured at a frequency range of 8.2~18GHz by E8362B PNA series network analyzer. The real part (ε ′ ) of the permittivity of the Csf/Si3N4 composites increases from 10 to 58 with the rise of the content of carbon fibers in the composites, as well as the imaginary part increases from 0.03 to 98 at frequency of 9.375GHz. A strong frequency dependence of the real part was observed both in X and Ku bands.

Abstract: Specimens of polyacrylonitrile-based carbon fiber (PAN-CF) with different graphitization temperatures were investigated by small angle X-ray scattering (SAXS) and wide angle X-ray diffraction (WAXD). Based on SAXS intensity data and fractal theory, surface fractal dimension of the pore in PAN-CF was given by small angle X-ray scattering intensity method, the size of various pores and the bigger pore percentage of unit volume were calculated by Fankuchen gradual tangent method. The result indicatesd that the size and surface fractal dimension of the pores, the bigger pore percentage of unit volume increased with increasing graphitization temperature. This forms stress concentration easily, which leads to the decreasing of tensile strength.

Abstract: This work is the first step to develop a programmable tactile array based on ER/MR fluid technology. Prototypes of display incorporating controllable fluids such as electrrheological (ER) fluid or magnetorheological (MR) fluid have been developed and investigated. Surface force responses of these tactile displays under various electric/magnetic fields have been measured while a probe moving across the upper surface. As the applied external electric or magnetic field varied, the sensed surface profiles changed in synchronisation with the field strength. With the controllable fluid actuator, the displayed surface information is stable and repeatable.