Key Engineering Materials Vols. 336-338

Abstract: Titanium diboride nanoparticles reinforced copper matrix composite by combustion synthesis technology from titanium, boron and copper powders without other activated methods. Thermodynamics of the system was calculated theoretically. It was found that TiB2 was stable phase in the composite and TiCu interphase compound can convert into stable phase. The phases of the synthesized product were identified using X-ray diffraction and the results showed that only TiB2 and Cu phases, no other phases existed in the product. It is consistent with the calculated result of thermodynamics. SEM microstructural characterization showed that a homogenous distribution of the titanium diboride nanoparticles in the copper matrix.

Abstract: The WC particulates (0.076mm~0.100mm in size) and carbon steel (0.45wt% C) are selected as a reinforced phase and matrix in the composites. The techniques of warm compaction are systematically investigated with powder metallurgy solid phase sintering method. The performance of sliding friction wear of the composites is tested on a pin on disk tester. The test results of warm compaction show that the composites sample containing 50% WC and 50% steel possesses the perfect compaction density (9.4362g/cm3) and the relative density reaches 91.6% under the condition of 140°C compaction temperature, 320KN stress, and lubricated with zinc stearate. The results of wear test show that the composite sample under the condition of warm compaction gains the best wear property, and the relative wear resistance is the 2.9 times of 15Cr cast iron, 2.6 times of 20Cr cast iron and 2.8 times of the composite sample under the condition of room temperature compaction. And the wear mechanism of the particle-reinforced composites is analyzed using SEM.

Abstract: Si3N4-filled epoxy resin composite was fabricated employing liquid press molding method. Properties, such as thermal conductivity, dielectric constant of Si3N4-filled epoxy resin composite were evaluated, the effect of the content of Si3N4 and surface treatment of the filler was also considered. A silane coupling agent, namely NH2−(CH2)3Si−(OC2H5)3, was applied to functionalize the surface of Si3N4 filler. Experimental results showed that the thermal conductivity of the composites is strongly dependent on the filler and is dominated by the interface of epoxy resin and Si3N4 particles. As the Si3N4 volume fraction increasing, thermal conductance of Si3N4-filled composite was improved obviously, especially for that of silane-treated Si3N4 powder filled composite. Dielectric constant of the composite increases linearly, however, it still remains at a relatively low level (<5, at 1MHz).

Abstract: Thermally conducting, but electrically insulating, polymer-matrix composites exhibiting low dielectric constant are needed for electronic packaging. For developing such composites, this work used silicon nitride particles as fillers and epoxy as matrix. The thermal conductivity of Si3N4 particles epoxy-matrix composites was increased by up to 31.4 times than that of neat polymer by silane surface treatment of the particles prior to composites fabrication. The increase in thermal conductivity is due to decrease in the filler-matrix thermal contact resistance through the improvement of the interface between matrix and particles. At 45.4 vol. % silane-treated Si3N4 particles only, the thermal conductivity of epoxy-matrix composites reached 9.72W/ (m*K). The dielectric constant was also low (up to 5.0 at 1 MHz). However, Si3N4 addition caused the flexural strength and ductility to decrease from the values of the neat polymer.

Abstract: The amount of marble dust occurred during machining and cutting of marble pieces and fly ash emitted from coal power plant is rather high and these wastes create significant environmental pollution. In fact, these wastes can be utilized in various industrial applications. In this study, various amount of fly ash, marble dust and polyester as base material, methyl ethyl keton peroxid as hardener and cobalt naphtanats as accelerator were used to produce polyester matrix composite material. Mechanical properties of composite materials were investigated and the optimum values were determined. In the first step of the manufacturing of composite material, the amounts of hardener, accelerator and polyester were kept constant and only fly ash/marble dust ratio was changed. The experimental results showed that while fly ash/marble dust ratio up to 1/3 was increased, the strength and hardness of the composite materials increased. Thus, the composite materials with high strength and hardness were produced. The optimum three point bending strength and hardness values were 30.42 N/mm2 and 98 Shore A, respectively. In the second step, the amounts of hardener, accelerator and fly ash/marble dust ratio were kept constant and the effects of the change in the amount of polyester were investigated. It was seen that the highest tree point bending strength and hardness were obtained at polyester/filler (marble dust +fly ash) ratio of 0,38. The optimum three point bending strength and hardness values were 32.78 N/mm2 and 99 Shore A, respectively.

Abstract: Among a variety of fiber sensors, the fiber Bragg grating (FBG) sensor has numerous advantages over other optical fiber sensors. One of the major advantages of this type of sensors is attributed to wavelength-encoded information given by the Bragg grating. Since the wavelength is an absolute parameter, signal from FBG may be processed such that its information remains immune to power fluctuations along the optical path. This inherent characteristic makes the FBG sensors very attractive for application in smart material structure, health monitoring field et al. But FBG sensors are sensitive to temperature and strain simultaneously; it is necessary to analyze the characteristics of temperature and strain of FBG applied for smart structure. Short overview of the FBG sensing principle as well as theoretical analyses is presented at first; then the paper proposes a simple, convenient, and low cost experimental method to verify the performance of FBGs. The improved high-accuracy experimental instrument of thermal deformation, which consists of an accurate temperature controlling and measuring subsystem, supporting and adjusting subsystem, collimating and positioning subsystem and fine motion and measuring sub-system, is simply introduced. The proposed experimental method involves bonding one uniform FBG to the center of the pole, which is about 89.5mm long; another FBG temperature sensor is free in the temperature-control box. The temperature in the box is -20°C-+50°C is adjusted according to experimental schedule. The characteristics of the FBG are analyzed by actual datum, which are simultaneously collected by a PC through a FBG interrogator. Comparing the data of FBG bonded to the pole with another FBG temperature sensor in the free state, the characteristics of the temperature and the thermal strain of the FBG can be obtained. The experimental result shows the FBGs used to the smart material have good agreement characteristics with theoretical calculation of the FBGs.

Abstract: The SiC/Si multilayer composites were fabricated successfully by reaction sintering method with normal stacked papers as the raw materials. Paper was cut into rectangular sheets and stacked, then infiltrated with phenolic resin to get a laminar structure. This paper /resin laminar composite was transformed into porous carbon with laminar structure after heating at 800 oC for 2h in N2 atmosphere. Finally this porous laminar carbon was reheated with silicon powder at 1450-1650oC for 1-2h in a vacuum furnace and SiC/Si multilayer composites can be obtained through the in-situ reaction between carbon and liquid silicon. The microstructure, reaction mechanism, phase composition and mechanical properties of these multilayer composites were researched. The final material shows a distingished laminar structure with alternating arrangement of SiC thick layers and silicon thin layers. SiC layer was composed by beta-SiC and a little of free silicon and carbon not reacted. The capillarity infiltration and in-situ reaction of liquid silicon act key roles in this process. Higher strength and non-catastrophic failure mode for this material were observed.

Abstract: MoSi2 is one of the few intermetallics to have potential for further systems. However, the use of MoSi2 has been hindered due to the brittle nature of the material at low temperatures, inadequate creep resistance at high temperatures, accelerated (pest) oxidation at temperatures between 450~ 550°C. In this investigation Mo(Al,Si2)/Ti3SiC2 composites has been prepared by reaction hot-pressing from Mo, Si, SiC, Ti, Al powder mixture under different temperatures. XRD results show that the main products are Mo(Si,Al)2 and Ti3SiC2. Part of TiC and SiC also appeared at low treating temperature. With the treating temperature increasing SiC disappeared. No evidence show lattice change of Mo(Si,Al)2. It must be the results of sufficient Al added. The electrical conductivity properties were also investigated. Samples treating under different temperatures showed different changes. Samples under high treating temperature showed a near linear change ranging from 27~800°C and Samples under low treating temperature showed a nonlinear change.

Abstract: Ti3SiC2/20vol%SiC composite was synthesized by spark plasma sintering (SPS) under a pressure of 50MPa at 1350°C using Ti, Si and C as starting powders. The phase constituents and microstructures of the composite were investigated. X-ray diffraction (XRD) results demonstrated that Ti reacted with C to form TiC firstly, then TiSi2 formed from Ti and Si. The formation of Ti3SiC2 might come from two reactions. One was that TiSi2, Ti and TiC reacted directly to form monolithic Ti3SiC2. The other one was that TiSi2, Ti and C reacted to form Ti3SiC2 and SiC. The EPMA results showed that the main phases were Ti3SiC2 and SiC with a minor content of TiC as impurity. TiC particles less than 1μm in diameter distributed in SiC phase.

Abstract: An interformational exfoliation behavior of the layered Ti3AlC2 induced by copper was firstly investigated via a “Cu-Ti3AlC2-Cu” sandwich sample infiltration-sintered at 1100oC to 1200oC. It was found that the molten Cu accelerates Ti3AlC2 to decompose, induces the interformational exfoliation to generate, and consequently forming a sub-micro-layered structure making up of TiC0.67 layers and Cu-Al alloy layers within a Ti3AlC2 grain. This interformational exfoliation behavior can be attributed to a topotactic mechanism due to the outward diffusion of Al the entering of Cu.