ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1995.tb03549.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryA new class of materials, formed by dispersion of low‐melting‐point metal alloys in a polymer matrix, has been studied from the point of view of microstructure, interfacial interaction and mechanical properties. The phases in these composites were formed in the same way as for polymer blends and were thus dependent on viscosity ratio, concentration, surface tension and interfacial interactions.Metal alloys of tin and bismuth (Sn/Bi) were mixed with high‐density polyethylene (HDPE) and polystyrene (PS) at elevated temperatures. Some preliminary investigations of lead and tin (Pb/Sn) alloys blended with HDPE, PS, polypropylene (PP), polyoxymethylene (POM), polyethylene‐terephtalate (PET), polymethylmethacrylate (PMMA), polycarbonate (PC), polyvinylidenefluoride (PVDF) and Polyvinylchloride (PVC) were also undertaken. The composites were characterized by light and electron microscopy, image analysis, electrical conductivity measurements and impact testing.It is shown that the low‐melting‐point metal alloys can be dispersed in polymers to a submicrometre level by blending. The particle size distribution follows an exponential function, which means that very fine as well as large particles are present. The equilibrium between dispersion and coalescence is very rapidly established during mixing. The average particle size can be controlled by the properties of the matrix, concentration of the metal and processing conditions.An investigation of interfaces revealed that in some cases a chemical interaction between the metal and the polymer can occur. This is apparent by observation of degradation, fluorescence and changes in mechanical

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1995.tb03550.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryThree methods, namely microphotoelasticimetry, Raman spectroscopy and surface microgrids, are currently used at ONERA on fibre‐reinforced polymers to measure thein‐situfibre or matrix deformation. They provide the materials scientist with valuable indications on the early damage growth. Recent results are given and information about the limitations of the methods are indica

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1995.tb03551.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryThe resin transfer moulding (RTM) process is becoming increasingly important for the manufacture of continuous fibre‐reinforced thermosetting resin matrix composites. The RTM process is a closed mould technique which reduces volatile emissions relative to traditional hand lay‐up methods. The fibres, generally as several layers of fabric, are prepared as a preform and laid in the closed mould. The resin is injected, at one or more points, and flows through the mould to form the finished product. In the manufacture of high‐performance composite structures, the flow of resin is constrained by the high volume fraction of reinforcement fibres required to achieve the performance. Commercial fabrics are becoming available which are woven with specially designed mesoscale architecture to promote flow of the resin. The flow rates in a series of such fabrics have been studied. The microstructures of the resulting composites have been examined using brightfield optical microscopy. A Quantimet image analyser was used to quantify the structures on both the mesoscale and the microscale. The flow rate has been shown to be related to the presence of both large and more modest sized pore space in the reinforcement archite

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1995.tb03552.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryThe microstructure and properties of uni‐directional pitch‐based carbon‐carbon composites are explained in terms of the chemical composition of pitch precursors. Pitches are characterized by standard procedures (elemental analysis, softening point and solubility tests), extrography which is a simple and rapid silica gel adsorption chromatographic technique, Fourier transform infra‐red and gas chromatography of the toluene‐soluble fraction. Pitch pyrolysis behaviour is monitored by hot‐stage microscopy. The main microstructural features of uni‐directional composites from pitches and commercial PAN‐based carbon fibres are determined by light microscopy and scanning elec

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1995.tb03553.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryA new Nicalon SiC‐based fibre, characterized by a low oxygen content (0–5% wt) has been studied. The absence in this fibre of a continuous Si–C–O phase, which characterized the previous NLM 202 series of fibres, induces larger mean sizes for the constituents: the fibre is composed of β‐SiC grains 5–20 run in diameter and turbostratic aggregates of carbon 2–5 nm in diameter. The fibre is seen to be suffer at room temperature (E= 300 GPa) and stronger due to a reduction in critical defects thanks to improvements in processing conditions. The Young's modulus remains almost stable up to 1473 K in air and above this temperature the core of the fibre exhibits continuous grain growth up to 1773 K, but without the degradation that occurred in the previous generation of fibres. Fibre strength was seen to be lowered when compared to room temperature values even when exposed in air to temperatures of 1073 K. A comparable fall is not seen with the NLM 202 fibres until 1273 K and this difference is attributed to the oxidation of the carbon‐rich surface of the new fibre. SiC is oxidized at higher temperatures, inducing, above 1473 K, the growth of a silica layer on the surface, with defects at the glass/ceramic interface. The large discrepancies between the good thermo‐mechanical characteristics in inert atmosphere and the behaviour in air may be reduced if a coating resistant to oxidation could be ap

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1995.tb03554.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryTwo experimental SiC fibre‐reinforced yttrium magnesium aluminosilicate (SiCf‐YMAS)‐type ceramic‐matrix composite (CMC) materials fabricated (i) by the glass process and (ii) by chemical precursor infiltration have been studied by light microscopy, transmission electron microscopy (TEM), high‐resolution electron microscopy (HREM) and energy‐dispersive X‐ray spectroscopy (EDS). The distribution of the fibres inside the composite as well as the average diameter of fibres have been determined by image analysis. The microstructure of the YMAS matrices has been characterized by TEM observations. YMAS matrices are formed of two main phases, cordierite and β‐yttrium silicate (Y2Si2O7). Two minor phases (mullite and spinel) have been found to crystallize inside the cordierite and the yttrium silicate crystals. Fibre‐matrix interfaces have been observed in HREM. A thin turbostratic carbon layer (20–30 nm) has been imaged in both composites at the fibre‐matrix interface. It crystallizes along the matrix interface and grows inside the fibre, forming a diffuse interphase. The carbon layer is believed to be the consequence of reaction between oxygen in the matrix and SiC nanocrystals

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1995.tb03555.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryA silicon carbide fibre‐reinforced glass‐ceramic composite, based upon a BaO–MgO–Al2O3–SiO2(BMAS) matrix, has been used for a study of microstructural stability (specifically interface stability) after environmental exposure at elevated temperature. Characterization of the as‐received material demonstrated the presence of a thin ‘carbon‐rich’ interfacial layer between fibre and matrix, as typically observed in glass‐ceramic/silicon carbide fibre composite systems. Samples have been subjected to heat‐treatments in an oxidizing atmosphere at temperatures between 723 and 1473 K, for up to 500 h. Intermediate‐temperature ageing, between 873 and 1073 K, results in strong fibre/matrix bonding, with consequent degradation of strength and composite ‘ductility’. This is due to oxidative removal of the carbon interfacial layer and subsequent oxidation of the fibre surface, forming a silica bridge. Carbon is retained at higher ageing temperatures due to the formation of a protective surface oxide scale at exposed fibre ends. Attempts to pretreat the BMAS composite at high temperature (1273–1473 K), designed to inhibit intermediate‐temperature degradation via the formation of silica plugs at exposed fibre ends, has given mixed results due to the high residual porosity content in these materials, allowing paths of ‘ea

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1995.tb03556.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryInterlayer phenomena, revealed by high‐voltage electron microscopy (HVEM) and high‐resolution electron microscopy (HREM), are presented as they occur in various SiC(Nicalon) fibre‐reinforced Duran glass composites (differing in the specific sol‐gel supported production processes). Their dependence on the production parameters and their influence on the materials properties are discussed, taking into account the results of scanning electron microscope (SEM)in situtensile tests.Besides graphitic carbon, textured to a variable degree and influencing the tensile behaviour, oxycarbide formation is indicated.A reactive matrix additive, such as, e.g. TiO2, resulted in a decrease in strength and a brittle behaviour, while the addition of ZrO2markedly improves the mechanical pro

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1995.tb03557.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryThe microstructure of a magnesium lithium aluminosilicate glass ceramic composite has been investigated by scanning electron microscopy and analytical transmission electron microscopy. Attention was focused on the as‐received material, showing that there is a non‐uniform distribution of the major silicate phases inside the matrix. The largest part is made of spodumene‐type crystals containing more than 4wt% Mg. A minor part of the matrix is made of micrometre‐sized crystallites of spodumene and cordierite. The spodumene is always sensitive to the electron beam irradiation. The morphology of the amorphized spodumene areas indicates that it may have crystallized during a later stage of the matrix formation, filling the gaps between cordierite crystallites. The third component of the matrix is made of carbon‐rich areas. They can be as large as 10 μm and they always include amorphous Mg‐rich silicates. However, they are mainly small (a few tens of nanometres in width) when located at grain boundaries of spodumene crystals. In this case the turbostratic carbon patches are also intimately mixed with an Mg‐rich amorphous silicate. The interface between the matrix and the fibres has also been analysed, its thickness changes from one to the other, and it is sometimes empty due to decohesion. When it is filled, its outer part contains mainly tubostratic carbon and the inner part is a mixture of silicon oxide and probably carbon. After creep at 1373K, the spodumene‐type crystals are larger and they are no longer sensitive to the electron beam. The cordierite areas appear to shrink and the amorphous patches which were mixed with carbon transform into small crystallites (1–10 μm). The areas next to the fibres are found to extend irregularly into the matrix, probably as a result of

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1995.tb03558.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY