Showing papers on "Whisker published in 1987"
Journal Article•
TL;DR: Etude du frittage sans pression et des proprietes mecaniques de composites d'alumine renforces par des trichites de SiC as mentioned in this paper.
Abstract: Etude du frittage sans pression et des proprietes mecaniques de composites d'alumine renforces par des trichites de SiC
140 citations
TL;DR: In this paper, ZrO2 particles were added to a toughened, whisker-reinforced ceramic matrix, and the results showed that the combination of these multiple toughening agents should result in ceramic composites tougher than (1) that achieved by either mechanism by itself or (2) the sum of two processes.
Abstract: Since the contribution of transformation toughening increases with the loca crack resistance (which is proportional to the toughness of the matrix), ZrO2 particles were added to a toughened, whisker-reinforced ceramic matrix. Analysis revealed that the combination of these multiple toughening agents should result in ceramic composites tougher than (1) that achieved by either mechanism by itself or (2) the sum of the two processes. The toughness of mullite could be increased 1.8-and 2.4-fold with a 20 vol% addition of ZrO2 particles or SiC whiskers, respectively. However, when 20 vol% of both ZrO2 particles and SiC whiskers were added, the toughness was increased at least 3-fold with monoclinic m-ZrO2 and by >5-fold with tetragonal t-ZrO2. The differences in the toughening achieved when t-ZrO2 vs m-ZrO2 is present in the SiC-whisker-reinforced mullite are attributed to differences in their interdependencies upon the whisker reinforcement.
115 citations
TL;DR: In this paper, the mechanical properties of bulk 60Sn-40Pb solder with and without the Cu6Sn5 intermetallic rods were tested in tension, at -196° C, 20° C and 125° C. The intermetallics had no effect on strength, but decreased elongation at lower temperatures.
Abstract: Hollow, Cu6Sn5 intermetallic rods form within molten 60Sn-40Pb solder when it reacts with Cu. It is suggested that these rods form at the Cu surface by a screw dislocation mechanism and break off into the bulk solder. Hollow hexagonal intermetallics result when the core of the rod dissolves away and fills with molten solder. The mechanical properties of bulk 60Sn-40Pb solder with and without the Cu6Sn5 intermetallic rods were tested in tension, at -196° C, 20° C, and 125° C. The intermetallics had no effect on strength, but decreased elongation at the lower temperatures. The intermetallics had a large effect on the fracture characteristics. At -196° C failures initiate by interfacial separation between the intermetallic and solder matrix. At 20° C failures initiate at cleaved intermetallic rods. At 125° C the intermetallic rods appear to have little effect on the mechanical properties.
93 citations
TL;DR: In this article, thermal shock testing of an alumina-20 vol% SiC whisker composite showed no decrease in flexural strength with temperature differences up to 900°C.
Abstract: Thermal shock testing of an alumina-20 vol% SiC whisker composite showed no decrease in flexural strength with temperature differences up to 900°C. Alumina, on the other hand, normally shows a significant decrease inflexural strength with a temperature change of >400°C. The improvement in the thermal shock resistance of the composite is believed attributable to the increased fracture toughness of this material.
81 citations
TL;DR: In this paper, the authors examined the deflection angles of cracks in a hot-pressed MoSi2 with 20 vol% vapor-liquid solid β-SiC whiskers to determine the degree to which they are affected by the whisker reinforcement.
Abstract: Crack propagation in SiC-whisker-reinforced MoSi2 was studied. In particular, the deflection angles of the cracks were examined to determine the degree to which they are affected by the whisker reinforcement. The composite studied was hot-pressed MoSi2 with 20 vol% vapor-liquid-solid β-SiC whiskers. A substantial difference was found between the deflection angles of cracks formed in the reinforced MoSi2 and those in a control sample with no whiskers, showing the process of crack deflection as an important, but not the only, toughening mechanism.
68 citations
TL;DR: In this paper, the effect of the whisker/matrix interfacial characteristics on the strengthening and toughening mechanisms is investigated. And the results show that a strong interfacial bond results in a composite exhibiting brittle behavior.
Abstract: Whisker-reinforced ceramic matrix composites have recently received a great deal of attention for applications as high temperature structural materials in, for example, advanced heat engines and high temperature energy conversion systems. For applications requiring mechanical reliability, the improvements that can be realized in fracture strength and fracture toughness are of great interest. Of particular importance for optimizing the mechanical reliability of these composites is the effect of the whisker/matrix interfacial characteristics on the strengthening and toughening mechanisms. Whisker reinforcements are primarily utilized to prevent catastrophic brittle failure by providing processes that dissipate energy during crack propagation. The degree of energy dissipation depends on the nature of the whisker/matrix interface, which can be controlled largely by the matrix chemistry, the whisker surface chemistry, and the processing parameters.It is generally believed that a strong interfacial bond results in a composite exhibiting brittle behavior. These composites usually have good fracture strengths but low fracture toughnesses. If the interfacial bond is weak, the composite will not fail in a catastrophic manner due to the activation of various energy dissipation processes. These latter composites tend to have high fracture toughnesses and low fracture strengths. Generally, the interface should be strong enough to transfer the load from the matrix to the whiskers, but weak enough to fail preferentially prior to failure. Thus, local damage occurs without catastrophic failure. It is therefore necessary to control the interfacial chemistry and bonding in order to optimize the overall mechanical performance of the composites.
40 citations
TL;DR: In this article, the thermal conductivity and diffusivity of silicon carbide reinforced mullite was shown to increase with the amount of whisker content, and the effect was much greater for vapor-liquid-solid (VLS) whiskers than for rice-hull (RH) whisker.
Abstract: The thermal conductivity and diffusivity of silicon carbide whisker reinforced mullite was shown to increase with whisker content. This effect was much greater for vapor-liquid-solid (VLS) whiskers than for rice-hull (RH) whiskers. This suggests that the thermal conductivity for the VLS whiskers was significantly higher than for the RH whiskers. Due to preferred orientation of the whiskers, thermal conductivity and diffusivity of the composite samples exhibited significant anisotropy.
38 citations
Patent•
06 Apr 1987TL;DR: In this article, a Silicon-carbide-whisker-reinforced cordierite ceramic products are prepared by uniformly incorporating the whiskers in the ceramic batch, forming the batch into a product preform, e.g. by extrusion, and firing the preform according to a process wherein the conversion of the oxide batch materials to Cordierite occurs under a non-oxidizing atmosphere.
Abstract: Silicon-carbide-whisker-reinforced cordierite ceramic products are prepared by uniformly incorporating the whiskers in the ceramic batch, forming the batch into a product preform, e.g. by extrusion, and firing the preform according to a process wherein the conversion of the oxide batch materials to cordierite occurs under a non-oxidizing atmosphere. Significant improvements in product strength and thermal downshock resistance are obtained.
32 citations
TL;DR: In this paper, the microstructure of a silicon carbide whisker (SiCw) reinforced 2124 aluminium metal matrix composite was characterized using scanning transmission electron microscopy (STEM).
Abstract: The microstructure of a silicon carbide whisker (SiCw) reinforced 2124 aluminium metal matrix composite was characterized using scanning transmission electron microscopy (STEM). The SiC whiskers ranged in length from approximately 2 to 10 µm, and demonstrated good bonding to the aluminium matrix. In a few cases, the interface between SiC whiskers and the aluminium matrix exhibited wavy characteristics. The size of subgrains in the aluminium matrix was found to be dependent upon that of SiC whiskers. In addition, two types of intermetallic compounds were observed in the composite.
31 citations
TL;DR: In this article, the influence of nickel on the growth of TiC whiskers obtained by the CVD process was studied and it was shown that the gradual capture by the growing whisker of liquid Ni-Ti-C alloy which is at its tip is the chief cause of the change in growth mechanism.
TL;DR: In this article, the tensile mechanical properties of long (up to 77 mm length) SiC whiskers were investigated using multiple-fracture testing and the Weibull modulus for intrinsic whisker fracture was determined to be in the range 3 to 4.
Abstract: The tensile mechanical properties of long (up to 77 mm length) SiC whiskers have been investigated using multiple-fracture testing. SiC whiskers fractured from two types of defects. Below approximately 10 GPa stress, fracture occurred from extraneous surface defects, such as foreign matter particles and growth appendages. Above 10 GPa, fracture initiated from intrinsic defects. The Weibull modulus for intrinsic whisker fracture was determined to be in the range 3 to 4. Tests on very long whiskers indicated a strength plateau at 16 GPa for intrinsic whisker fracture. A basic statistical fracture description for the intrinsic fracture of whiskers was derived, which predicts a plateau in the intrinsic whisker strength.
TL;DR: In this article, a Silicon carbide whisker-reinforced Al2O3 composites were prepared using a processing scheme in which the constituents were dispersed in nonaqueous media, then colloid-pressed and pressureless-sintered under an inert atmosphere.
Abstract: Silicon carbide whisker-reinforced Al2O3 Composites were prepared using a processing scheme in which the constituents were dispersed in nonaqueous media, then colloid-pressed and pressureless-sintered under an inert atmosphere. Novel oligomeric and polymeric dispersants were used to sterically stabilize the SiC whiskers in the presence of the Al2O3 powder. The sintering studies indicated that in the absence of a suitable sintering aid, the whiskers significantly inhibited densification of the Al2O3 matrix. Doped composites containing yttrium isopmpoxide as a sintering aid were pressureless-sintered to final densities 95% of theoretical.
Patent•
06 Jul 1987TL;DR: In this paper, a process for preparing mullite, 3Al2 O3.2SiO2, whiskers by forming an intimate, anhydrous mixture of AlF3 and SiO2 powders in about a 12:13 molar ratio was presented.
Abstract: A process for preparing mullite, 3Al2 O3.2SiO2, whiskers by (1) forming an intimate, anhydrous mixture of AlF3 and SiO2 powders in about a 12:13 molar ratio; (2) heating the mixture in an anhydrous, SiF4 atmosphere at about 700° C. to about 950° C. to form barlike crystalline topaz, Al2 (SiO4)F2 ; and (3) heating the barlike crystalline topaz under anhydrous conditions in a SiF4 atmosphere at a temperature of from about 1150° C. to about 1400° C. to produce mullite whiskers. The mullite whiskers produced can be used in ceramic and metal matrices without further chemical treatment.
Patent•
28 Sep 1987TL;DR: In this paper, a whisker-reinforced zirconia-mullite composite article exhibiting excellent high-temperature modulus of rupture strength and good toughness is provided from batches comprising the free oxides ZrO2, SiO2 and Al2 O3 in combination with SiC whiskers for reinforcement.
Abstract: Whisker-reinforced zirconia-mullite ceramic articles exhibiting excellent high-temperature modulus of rupture strength and good toughness are provided from batches comprising the free oxides ZrO2, SiO2 and Al2 O3 in combination with SiC whiskers for reinforcement. Due to the fine oxide particle sizes attainable and the fact that the mullite is formed in situ in the consolidation process, dense, whisker-reinforced mullite composite articles exhibiting excellent high-temperature strength and toughness may conveniently be obtained.
TL;DR: In this article, a fabrication process for SiC whisker reinforced aluminium composites is developed, where the first step involves preforming the SiC Whisker and squeeze-infiltrating the molten metal into the preform.
Abstract: A fabrication process for SiC whisker reinforced aluminium composites is being developed. Theftrst step involves preforming the SiC whisker and squeeze-infiltrating the molten metal into the preform. Secondary fabrication can involve a conventional hot metal working practice such as extrusion. Microscopic observations indicate that the distribution of whiskers is very homogeneous. In an aluminium alloy (AA 6061) matrix composite containing 17 vol.-% SiC whiskers, the Young's modulus is > 100 GPa and the tensile strength increases by ~ 50–70% above that of the matrix to 460 and 529 MN m−2 in the cast and extruded products, respectively. The strength at elevated temperature and the wear resistance are also improved. These enhanced properties make the composite potentially suitable for a number of automotive applications.MST/574
Patent•
16 Jun 1987
TL;DR: In this paper, it has been found that coating with a thin surface layer protects the whisker material against chemical attacks and provides a possibility to make better use of the inherent good properties of whisker reinforced ceramics.
Abstract: The present disclosure relates to whisker reinforced ceramics preferably based upon pure oxide ceramics or mixed ceramics, which by means of coating with a thin wear resistant surface layer have obtained improved performance. It has been found that coating with a thin surface layer protects the whisker material against chemical attacks and provides a possibility to make better use of the inherent good properties of whisker reinforced ceramics.
Patent•
08 May 1987TL;DR: In this article, a fiber-reinforced ceramic matrix composites incorporating a glass-ceramic matrix of lithium aluminosilicate composition is disposed a fiber reinforcement phase including at least one layer of unidirectionally oriented fibers (e.g. SiC), the matrix further comprising a whisker reinforcement phase selected from the group of SiC, alumina, HfC and Si3 N4, the whiskers imparting substantially improved transverse modulus of rupture strength and interlaminar shear strength.
Abstract: Fiber-reinforced ceramic matrix composites incorporating a glass-ceramic matrix of lithium aluminosilicate composition in which is disposed a fiber reinforcement phase including at least one layer of unidirectionally oriented fibers (e.g. SiC), the matrix further comprising a whisker reinforcement phase selected from the group of SiC, alumina, HfC and Si3 N4, the whiskers imparting substantially improved transverse modulus of rupture strength and interlaminar shear strength to the composite.
TL;DR: In this paper, the removal of particulate impurities from whiskers by sedimentation and for mixing whiskers and ceramic powder are described with reference to three types of commercially available whiskers.
TL;DR: In this paper, it was shown that carbon whiskers with diameters of order 15 nm and remarkably high aspect ratios on graphite surfaces in 1 keV sputtering systems can grow in length at a constant rate with little or no increase in their diameter, provided that possible attachment sites on the sides of the whiskers are bound.
TL;DR: In this paper, a synchrotron X-ray topography of ZnS crystal whiskers has been studied using continuous radiation and cylindrical camera geometry, providing information on lattice symmetry and polytype order as well as local lattice perfection in the whisker.
Abstract: ZnS crystal whiskers grown from the vapour at about 1450 K, with typical lengths of about 20 mm and diameters about 100 μm, have been studied by synchrotron X-ray topography. Crystallographic structure and texture have been compared with morphological and optical characteristics point-by-point along whisker axes. Using continuous radiation and cylindrical camera geometry, entire diffraction patterns from zones of type have been recorded, providing information on lattice symmetry and polytype order as well as on local lattice perfection in the whisker. The X-ray topographs spanned the three main types of structure in vapour-grown ZnS whiskers, namely an initial region of usually faulted 2H structure, a following region (of ‘striated’ appearance, optically) consisting of a stack of lamellae (average thickness a few μm) of polytypic structures with various c-axis repeat periods, and a third, following region containing long-period polytypes, all of the same order, in which individual structures can ...
TL;DR: In this paper, the vapor-liquid-solid process was used to produce twinned SiC in the cubic form as a byproduct of the corrosion of silicon nitride, and their properties related to their use in reinforced materials were characterized.
Abstract: Whiskers of twinned SiC in the cubic form were produced by the vapor-liquid-solid process as a byproduct of the corrosion of silicon nitride. These whiskers were characterized and their properties related to their use in reinforced materials.
TL;DR: In this article, the optimum growth conditions for needle-like or wool-like Al2O3 whiskers were examined and a variety of crystal morphologies were also shown and described with respect to the experimental conditions.
Abstract: Needle-like or wool-like Al2O3 whiskers can be grown on a substrate by the hydrolysis of aluminium fluoride vapour. Effects of the growth conditions on the morphology of the crystals and growth processes of the whisker were investigated, and the optimum growth condition of whiskers was examined. Adequate vapour pressure conditions of the reactant gases for the growth of the wool-like whisker were found to be
$$P_{AIF_3 } \times P_{H_2 O}^{3/2}< 3.0 \times 10^{ - 3} (torr^2 )$$
. Aluminium oxyfluoride was assumed to be the most probable intermediate species for the growth of Al2O3 whiskers. A variety of crystal morphologies are also shown and described with respect to the experimental conditions.
TL;DR: In this paper, the tensile properties and wear resistance of SiC whisker-reinforced Al alloy 4032 composites were investigated, and the elastic modulus of T 6 heat treated SiC/4032 composite can be expressed as E(GPa) = 180Vf(vol pct) + 85.
Abstract: The tensile properties and wear resistance of SiC whisker-reinforced Al alloy 4032 composites were investigated. The elastic modulus of T 6 heat treated SiC/4032 composites can be expressed as E(GPa) = 180Vf(vol pct) + 85. The wear loss of SiC/4032 composites decreases rapidly with an increase in the volume fraction of SiC whisker up to 14 percent, beyond which it remains unchanged. The addition of BN gives rise to the degradation of the mechanical properties and of the coefficient of friction, which improves the wear resistance of the composites. The wear resistance of SiC/4032 composites depends remarkably on the size and distribution of Si particles in the Al alloy 4032 matrix. 20 references.
01 Jan 1987
TL;DR: Silicon carbide whisker-reinforced alumina composites have been shown to be significantly more creep-resistant than single phase alumina, although creep strains to failure are lower.
Abstract: Silicon carbide whisker-reinforced alumina composites have been shown to be significantly more creep-resistant than single phase alumina, although creep strains to failure are lower.1 Failure during creep apparently originates at processing flaws in the composites, which consist primarily of whisker nests and alumina agglomerates. Procedures to reduce the flaw population by use of dispersion processing techniques have been developed. Mixed dispersions of alumina powder and silicon carbide whiskers are pressure-filtered and subsequently hot-pressed in graphite dies. The resulting composites exhibit comparable creep resistance together with significantly greater creep failure strains than externally obtained hot-pressed samples. The oxidation of the composies under creep conditions is discussed.
01 Jan 1987
TL;DR: Alumina-SiC whisker composites have high fracture toughness and strength up to elevated temperatures and consequently have great potential for use in structural components as discussed by the authors, and are resistant to thermal shock, slow crack growth4 and creep.
Abstract: Alumina-SiC whisker composites have high fracture toughness and strength up to elevated temperatures and consequently have great potential for use in structural components.1–4 In addition, the composites are resistant to thermal shock, 5 slow crack growth4 and creep. 6
Patent•
06 Jul 1987TL;DR: A whisker of molybdenum oxide in the form of a filament, rod, or flake is a very strong crystal which is expected to be useful as a filler for plastics and for a variety of other applications as discussed by the authors.
Abstract: A whisker of molybdenum oxide in the form of a filament, rod or flake. Molybdenum oxide whiskers are produced by firing metallic molybdenum at a temperature of at least 400° C., preferably at least 800° C., in an atmosphere containing oxygen, or by firing an organic molybdenum compound in an atmosphere containing oxygen at a temperature which is at least equal to its thermal decomposition temperature. They are very strong crystals which are expected to be useful as a filler for plastics and for a variety of other applications.
Patent•
24 Feb 1987
TL;DR: An improved composite material consisting of silicon nitride whiskers uniformly dispersed through a glass matrix and a method for making the composite which comprises the step of dispersing the whiskers in a suitable liquid and separating off the fines and, optionally, treating the dispersed whiskers with HF is described in this paper.
Abstract: An improved composite material consisting of silicon nitride whiskers uniformly dispersed through a glass matrix and a method for making the composite which comprises the step of dispersing the whiskers in a suitable liquid and separating off the fines and, optionally, the step of treating the dispersed whiskers with HF.
Patent•
13 Oct 1987
TL;DR: In this article, the authors proposed a method to obtain the title composition having excellent adhesivity and flexibil ity and useful as a conductive ink or conductive paint, by compounding carbon whisker, expanded graphite, carbon black, etc., to a resin as a binder, a filler and a solvent, etc.
Abstract: PURPOSE: To obtain the title composition having excellent adhesivity and flexibil ity and useful as a conductive ink or conductive paint, by compounding carbon whisker, expanded graphite, carbon black, etc., to a resin as a binder, a filler and a solvent, etc. CONSTITUTION: The objective composition is produced by adding and kneading (A) carbon whisker (preferably graphite whisker) produced by growing a whisker from a hydrocarbon in a space heated at 1,000W1,400°C using fine particle of iron, nickel, etc., as a catalyst or growth nucleus, (B) an expanded graphite produced e.g. by crushing natural flake graphite to particle diameter of ≤5μm, immersing in a sulfate and quickly heating at 900W1,100°C to effect the expansion and (C) a conductive carbon-based filler such as carbon black and/or graphite powder to a resin as a binder, an additive, a solvent, etc. The amount of the components A and B are 20W80wt.% and 10W70wt.% based on A+B+C, respectively. COPYRIGHT: (C)1989,JPO&Japio