SiC Fraction Research Articles

Consumption of SiC whiskers by the Al–SiC reaction in aluminium-matrix SiC whisker composites

The Al–SiC reaction in aluminium-matrix SiC composites made by liquid metal infiltration resulted in the formation of silicon, the amount of which increased with increasing SiC volume fraction, but the fraction of SiC consumed by the reaction increased with decreasing SiC volume fraction. For SiC whisker composites made at an infiltration temperature of 800 °C, the fraction of SiC consumed was 18, 26 and 55% at SiC volume fractions of 0.31,0.23 and 0.10, respectively. The fraction of SiC whiskers consumed was inversely proportional to the volume fraction of SiC whiskers in the composite. The product of these two fractions provides a scale (called the reactivity index) that describes the Al–SiC reactivity. The index decreased with decreasing infiltration temperature and was higher for SiC whiskers than SiC particles. Even at an infiltration temperature of 670 °C, the fraction of SiC whiskers consumed was 26% at an SiC volume fraction of 0.10. In contrast, the fraction of SiC consumed was only 8.4% for a 55 vol.% SiC particle composite made at an infiltration temperature of 800 °C. The fractional consumption values were obtained by determining the silicon concentration in the aluminium matrix via calorimetric measurement of the liquidus-eutectic temperature difference.

Microfracture Analysis of SiC Reinforced Glass Composites by Acoustic Emission

SiC particulate reinforced glass matrix composites were fabricated by hot pressing. The volume fraction of SiC was changed from 0% to 30%. The elastic modulus of the fabricated composites was consistent with a law of mixture based on the micromechanics. In order to evaluate the mechanical properties of the materials we measured four-point bending strength and fracture toughness (K IC ) by Single Edge Pre-cracked Beam (SEPB) method. Acoustic emission (AE) tests were performed during four-point bending and fracture toughness tests We observed fracture surfaces after bending tests. The bending strength increased with increasing volume fraction of SiC particle. The bending strength of glass was 96MPa and that of the composite reinforced with 30 vol % SiC particle was 144 MPa. The fracture toughness K IC also increased with increasing volume fraction of SiC particle. The fracture toughness K IC of the composite reinforced with 30vol% SiC particle was 2.1 MPam 1/2 . The number of AE events increased with increasing volume fraction of SiC particle. However AE behavior during bending tests is different from that during fracture toughness tests The total number of AE during fracture toughness tests is more than that during bending tests.

SiCウィスカー強化Al<SUB>2</SUB>O<SUB>3</SUB>セラミックスにおける内部摩擦の振幅依存性

Mechanical properties of SiC-whisker-reinforced Al2O3 ceramics were investigated with attention to the volume fraction of SiC whiskers. Experimental results show that the fracture stress and the Young’s modulus increased, while the internal friction decreased, monotonously with increasing volume fraction of SiC whiskers.The date on the amplitude-dependent internal friction were analyzed on the basis of the microplasticity theory and converted into the plastic strain expressed as a function of stress. This enables one to evaluate non-destructively the stress-strain relation in the forerunning process of fracture of the ceramic composite. The microflow stress at the plastic strain of 1×10−10 increased linearly with increasing volume fraction of SiC whiskers up to 30%. Since the amplitude-dependent internal friction can be measured in the range of elastic deformation, the microflow stress is always reproducible and unaffected by an accidental propagation of the localized crack. However, the variation of microflow stress with the volume fraction corresponds to that of the fracture stress obtained by the three-point bending test. Therefore, it becomes possible to study the mechanical property leading to fracture based on the measurement of amplitude-dependent internal friction in whisker-reinforced ceramics.

Wear behavior of reinforced aluminum alloys in various impact loadings

The wear behavior of SiC particulate-reinforced 2024A1 and Al 2O 3- SiO 2 short fiber-reinforced SC 122A (ASTM) aluminum alloy composites has been investigated in three tests with various impact loadings: (1) sliding wear; (2) impact abrasion; (3) sand-blasting erosion. The results showed that in sliding with a steady load, the wear resistance of the composites was markedly better than that of the matrix alloys and increased with increasing volume fraction of SiC; with increasing impact component in loading, the wear resistance of the composites worsened rapidly. In the impact abrasion test, no obvious improvement in the wear resistance of the composites was found; in the sand blasting erosion test, the wear resistance of the composites was much worse than that of the matrix alloys, and decreased with increasing volume fraction of SiC. The reinforcing effectiveness of the fibers was better than that of the particles under steady loading, but worse under dynamic loadings.

The effect of fabrication techniques on the properties of Al-SiC composites

This study focusses on silicon carbide particulate-reinforced metal-matrix composites fabricated using four different powder metallurgy techniques. The effect of the fabrication method on the mechanical properties of the near net shape specimens was investigated.Sinter/hot isostatically pressed (sinter/HIPed) composites of up to 30 vol.% SiC were produced with a significant improvement in ductility and ultimate tensile strength compared with the other fabrication methods. The poor mechanical properties of composites produced by the other methods is attributed to the weak bonding between adjacent particles and to internal porosity. The measured densities of the fabricated materials indicated that fully dense material was not achieved. For composites with less than 10% volume fraction of SiC, the density was relatively independent of the fabrication method adopted.Microstructural examination of fracture surfaces in representative materials confirmed that the sinter/HIPing technique yielded the best composites. For particle loading less than 10% volume fraction, ductile failure of the matrix appears to be the limiting factor. At higher volume fractions, the strength of interfacial bonds, initiation and growth of voids, and particle cracking all play an important role in controlling the mechanical properties.

Elevated-temperature mechanical behavior of plasma-sprayed MoSi 2SiC

The elevated-temperature mechanical behavior of a plasma-sprayed MoSi 2-9vol.%SiC particulate composite was investigated over the temperature range 1100–1500°C. At temperatures of 1200 °C or less the stress exponent of 2.3–2.5, grain size exponent of −2.2, activation energy for creep of about 300 kJ mol −1, equiaxed grains after deformation and no deformation-induced dislocations suggest grain boundary sliding controlled by lattice diffusion of either Mo or Si as the dominant deformation mechanism. At temperatures of above 1300 °C the stress exponent is 1.3–1.5 and the activation energy for creep is 190 kJ mol −1. It is believed that the dominant deformation mechanism in this temperature range is grain boundary sliding controlled by grain boundary diffusion. The decrease in the stress exponent and activation energy for creep is thought to be a result of melting or softening of an amorphous silica grain boundary phase. The creep resistance of the plasma-sprayed MoSi 2SiC composite is lower than that for MoSi 2SiC composites produced using powder metallurgy and in-situ techniques as a result of its finer grain size and/or lower volume fraction of SiC.

Effect of microstructure (particulate size and volume fraction) and counterface material on the sliding wear resistance of particulate-reinforced aluminum matrix composites

The effects of microstructure (namely, particulate volume fraction and particulate size) and the counterface materials on the dry-sliding wear resistance of the aluminum matrix composites 2014A1-SiC and 6061Al-Al2O3 were studied. Experiments were performed within a load range of 0.9 to 350 N at a constant sliding velocity of 0.2 ms-1. Two types of counterface materials, SAE 52100 bearing steel and mullite, were used. At low loads, where particles act as loadbearing constituents, the wear resistance of the 2014A1 reinforced with 15.8 µm diameter SiC was superior to that of the alloy with the same volume fraction of SiC but with 2.4 µm diameter. The wear rates of the composites worn against a steel slider were lower compared with those worn against a mullite slider because of the formation of iron-rich layers that act asin situ solid lubricants in the former case. With increasing the applied load, SiC and A12O3 particles fractured and the wear rates of the composites increased to levels comparable to those of unreinforced matrix alloys. The transition to this regime was delayed to higher loads in the composites with a higher volume percentage of particles. Concurrent with particle fracture, large strains and strain gradients were generated within the aluminum layers adjacent to contact surfaces. This led to the subsurface crack growth and delamination. Because the particles and interfaces provided preferential sites for subsurface crack initiation and growth and because of the propensity of the broken particles to act as third-body abrasive elements at the contact surfaces, no improvement of the wear resistance was observed in the composites in this regime relative to unreinforced aluminum alloys. A second transition, to severe wear, occurred at higher loads when the contact surface temperature exceeded a critical value. The transition loads (and temperatures) were higher in the composites. The alloys with higher volume fraction of reinforcement provided better resistance to severe wear. Wearing the materials against a mullite counterface, which has a smaller thermal conductivity than a counterface made of steel, led to the occurrence of severe wear at lower loads.

Cooperative behavior during ferroelectric transitions in KNO3 powder

Experimental evidence of cooperative behavior during the ferroelectric phase transitions in granular and powder KNO3 at atmospheric pressure is presented. Three different experimental studies were performed in which phase transitions were detected and characterized by heat flow calorimetry: (1) the distribution of SiC powder in granular KNO3 was varied; (2) the volume fraction of SiC in powdered KNO3 was varied; and (3) pure KNO3 powder was thermally cycled. All three studies provided evidence of cooperative behavior between the KNO3 particles during the III-II phase transition. The cooperative behavior reduced the temperature range of phase III stability from ∼97–124 °C to that characteristic of bulk material (∼110–124 °C). Separate KNO3 particles behaved as individual ferroelectric domains, with each particle making the phase transition independently near the expected Curie temperature. Particles of KNO3 in intimate physical contact tended to behave cooperatively as a single large ferroelectric domain leading to sharper phase transitions more characteristic of single crystals. The degree of cooperative behavior was dependent upon the extent to which the individual particles were in physical contact. The absence of the III-II phase transition in KNO3 powder that has been reported in the literature can be understood from the results obtained using SiC powder to separate KNO3 particles during heat flow calorimetry measurements.

Quantitative measure of mixture homogeneity of an alumina silicon carbide composite

Homogeneity, defined in terms of spatial distribution uniformity of one phase or component within another, can be determined from the variation of the standard deviation of the measured volume fraction of one component with sampling area. We have applied this concept to the evaluation of dispersions of Sic whiskers in an alumina matrix by using energy dispersive x-ray spectroscopy (EDS) . The quantitative analysis measures the area to area variation in SiC fraction. The homogeneity distribution was obtained by calculating the variance in this fraction as a function of magnification (sampling area) in a scanning electron microscope. These data are compared to calculations of expected values based on a Poisson distribution model for the dispersion of SiC.Compositions were prepared from two different SiC size distributions. The blending procedures and volume fractions (0.30) were the same for each composition. Six polished specimens were analyzed from each of two 100mm diameter hot-pressed alumina - SiC billets.

Localized deformation of SiCAl composites

Tensile tests of SiC-6061 Al composites containing various volume fractions of whiskers or particles (20, 5 and 0 vol.%) showed that for samples containing a high volume fraction (20 vol.%) the fracture process was very localized, i.e. a very narrow neck. As the volume fraction of whiskers or particles decreased, the deformed region spread out. One might expect that the microstructure should correspond to the macroscale changes. In the highly deformed region the dislocation density is expected to be higher, in the less deformed regions the dislocation density should be lower, and if the deformation is very localized, then the high dislocation density should also be limited to a very narrow region. Overall, there is good agreement between the microstructure (dislocation density) change and the macroscale deformation of SiCAl composite tensile samples. The mechanism proposed to account for this change in deformation behavior as a function of volume fraction of SiC in aluminum is related to the expansion of the plastic zone (due to differences in thermal coefficients of expansion between SiC and aluminum) when the external stress is applied. Also, the localized deformation is related to localized clusters of SiC particles. There is a cooperative effect which leads to a region of very localized plastic deformation.

高温超強度Ｓｉ３Ｎ４‐ＳｉＣナノ複合材料

Effects of nano-size dispersions on mechanical properties such as hardness, fracture toughness and strength were investigated for the Si3N4-SiC nanocomposite system. The Si3N, -SiC nanocomposites were fabricated by hot-pressing the mixtures of amorphous Si-C-N precursor powder with various C/N ratio and sintering additives. Transmisson electron microscopic observation indicated that the Sic particles less than approximately 0.1μm in diameter were dispersed whithin the Si3N4, matrix grains. No apparent impurity phases was observed at the intertfaces of Si3N4 and Sic. The grain morphology of Si3N4 was strongly influenced by the Sic dispersion, indicating that the formation of elongated and equiaxed Si3N4 grains was acceralated at the lower and higher SiC volume fractions, respectively. As expected from this change of grain morphology, the fracture toughness and strength were showed the maxmima, 155OMPa and 6.5MPam1/2, at the certain volume fraction of SiC. The high-temperature strength was also improved by the Sic dispersion and the high strength of over 1GPa was observed even at 1400°C.

Interstellar SiC in the Murchison and Murray meteorites: Isotopic composition of Ne, Xe, Si, C, and N

Five SiC fractions were isolated from the Murray and Murchison C2 chondrites, and were examined by noble-gas and ion-probe mass spectrometry as well as by SEM-EDX. The SiC (totalling ~6–9 ppm of the meteorites) contains record concentrations of the exotic components Ne-E(H) (nearly monoisotopic Ne 22) and Xe-S (enriched in isotopes 128, 130, 132), which are located in coarse- and finegrained SiC, respectively. The Ne 21-content exceeds up to 40-fold that expected from the recent cosmicray irradiation, implying a presolar cosmic-ray exposure age of 39 (+19, −13) Ma. This age is much shorter than the predicted ~500 Ma lifetime of refractory interstellar grains and implies one of the following: a selective interstellar destruction process for SiC, enhanced supernova activity in the protosolar neighborhood, or late outgassing of >90% of the SiC. Si, C, and N all have highly anomalous and variable isotopic compositions, varying by 1.4×, 16×, and 120×. Analysis of 12 single, mainly monocrystalline grains (which must be endmembers) shows that at least 4 and probably ≥6 independent Si components are present, corresponding to a like number of individual stars. As SiC is stable only at C O ≥ 0.83 (nearly 2× solar), its parent stars must be mainly carbon-rich red giants. The mean C 12 C 13 ratio of SiC indeed resembles that of present-day carbon stars and interstellar gas (44 ± 3 vs. 45 ± 4 and 43 ± 4), but in view of the ~4.6 × 10 9 y difference in age, this agreement is surprising. Correlations between C 12 C 13 and N 14 N 15 show mainly the signature of hydrostatic H-burning followed by early stages of He-burning (red giants), less commonly explosive H-burning (novae) or advanced stages of He-burning (Wolf-Rayet stars, Type II supernovae). The first two stellar types could also account for Xe-S and Ne-E, respectively. Meteorites contain only 4 × 10 −5 of their Si as SiC, in contrast to an estimated value of ~1 3 for fresh interstellar matter. Some selective destruction process is required, either in interstellar space or in the early solar system.

Non-enzymatic glycosylation influences Hb S polymerization.

In vivo glycosylated components of Hb S were isolated from red cell hemolysates of sickle cell anemia patients by application of affinity chromatographic and cation exchange chromatographic techniques. The total glycosylated fraction (GHb) of the whole hemolysate, Hb SIc, Hb So-glycosylated (formed mostly by glycosylation epsilon-NH2 groups of lysyl residues), and Hb So-nonglycosylated fractions were isolated in this manner. GHb contained about 33% Hb SIc and 42% Hb So (Hb So-glycosylated) and the rest was glycosylated Hb F and Hb A2. As expected, the binding of 2,3-DPG was affected only in Hb SIc and not in Hb So-glycosylated. Hb SIc and Hb So-glycosylated had higher solubility in concentrated phosphate solutions and had higher minimum gelling concentrations than the non-glycosylated form of Hb So. These effects are interpreted to be due to modification by glycosylation of specific sites that are directly or indirectly involved in the intermolecular contacts.

Ways of improving the quality of 80% Ni-20% Cr alloy coatings

It has been established that recrystallization annealing increases at of an 80/20 alloy/ substrate composite and decreases its τs and, consequently, such heat treatment may be beneficial to parts provided with “skins” but not to coating/substrate composites. A study was made of the structural changes induced by the reaction of SiC powder with the substrate material investigated during recrystallization annealing. It is shown that the strength of adhesion σad of an 80/20 alloy coating to its substrate can be increased by blasting the latter with a coarse SiC fraction (800–1000 µm).

Subcellular localization of LH releasing activity in the rat hypothalamus.

Separation of particulate fractions associated with LH releasing activity has been effected by differential centrifugation followed by sucrose density gradient centrifugation. The fractions were monitored for LH releasing activity by an in vitro incubation with rat pituitaries and for subcellular organelles by electron microscopy. LH released into the incubation medium and contained in the pituitaries was measured by radioimmunoassay (RIA). After differential centrifugation only the "crude mitochondrial fraction" caused an increase of LH release accompanied by a depletion of pituitary LH and a rise in total LH. Further fractionation of this pellet on a discontinuous sucrose gradient resulted in three opaque bands and three clear areas which were removed as sic fractions. Only one fraction, not associated with myelin, synaptosomes, or mitochondria, caused an increase in LH release and total LH while pituitary LH remained unchanged. This fraction appears to be predominantly composed of electron dense vesicles of varying sizes. Also of interest is another fraction which decreased LH release and was again not associated with myelin, synaptosomes, or mitochondria. The decreased release was associated with an increased pituitary LH while total LH remained unchanged. Of the six subcellular fractions obtained from the "crude mitochondrial pellet" only these two caused significant changes in LH release. Two other neural tissues, the cerebellum and cerebral cortex, were similarly processed. None of these subcellular fractions significantly altered LH release and/or synthesis.