Other Infiltration Products

• Influence of Liquid Metal Infiltration on the Superconducting Characteristics of Niobium Nitride, L.T. Summers, J.R. Miller, M.J. Strum, R.J. Weimer, and D.E. Kizer, Advances in Cryogenic Engineering, Plenum Press, Vol 34, 1988, p 835-842. A fully stabilized multifilamentary BN superconductor was prepared using a combination of physical vapor deposition of NbN on graphite followed by liquid metal infiltration using copper or aluminum. The resulting conductor assumed a finely divided multifilamentary form embedded in a matrix of conducting copper or aluminum. The geometry provides high stability to flux jumps and high quench protection. The effects of liquid metal infiltration and process variables on the electrical properties were determined. Critical current dependence on field strength and stabilizer residual resistivity ratio are discussed.

• Anomalous Growth of the Complex Carbide Phase in Carbon-Deficient WC-Co Hard Metal during Infiltration of Eutectic Liquid, J.K. Park, K.Y. Eun, and D.N. Yoon, Mater. Sci. Eng. A, Vol 105-106, 1988, p 233-236. Large angular grains of '/phase (Co3W3C) around WC grains formed during infiltration of the carbon-deficient 97WC-3Co with 25WC-75Co infiltrants. In contrast, in the uninfiltrated region, the fine ''/ and C0W3C phases were uniformly distributed. Some elongated '/grains grew at the infiltration boundary. The anomalous growth of '/phase is attributed to the composition change in the specimen from WC to '/to potassium region to the WC-K liquid region during infiltration.

• Correlation Among Process Routes, Microstructures, and Properties of Chemically Vapor Deposited Silicon Carbide, R.F. Davis, Chemical Vapor Deposition on Refractory Metals and Ceramics Symp., 29 Nov-1 Dec 1989 (Boston, MA), T.M. Besmann and B.M. Gallois, Materials Research Society, 1990, p 145-158. Silicon carbide is a generic term for a host of different materials produced by several process routes that yield a variety of microstructures and associated property characteristics. The route of chemical vapor deposition (CVD) is used primarily to deposit SiC for wear- and corrosion-resistant coatings and for diffusion barriers to and from the underlying substrate. Presently this technique is also being used to deposit monocrystalline semiconductor thin films of SiC and to infiltrate various high temperature woven fabrics. The paper describes the results of thermodynamic calculations to define SiC CVD diagrams using various precursor gas mixtures, discuss various CVD techniques, and detail the results of deformation, infiltration, and thin film deposition studies that have been recently conducted on vapor deposited SiC.

• Fabrication Aspects of Glass Matrix Composites for Gas Turbine Applications, D.A. Clarke, New Materials and Their Applications 1990, Proc. of the 2nd Int. Symp., 10-12 April 1990 (Warwick, U.K.), D. Holland, Ed., IOP Publishing, Bristol, U.K., 1990, p 173-183. A brief background to the development of glass matrix composites (GMCs) including the basic fabrication methods is presented. Some of the key problems involved in manufacturing production quantities of GMC gas turbine components are described and the need for highly repeatable, and hence largely automated, processing methods are highlighted.

• Processing and Properties of Silicon Carbide-Reinforced Aluminum Metal Matrix Composites for Electronic Applications, K.K. Aghajanian, Proc. 1991 Int. Symp. Microelectronics, International Society of Hybrid Microelectronics, Reston, VA, 1991, p 368-372. Alternative packaging materials with high thermal conductivity, high specific strength and stiffness, and low density are in demand for the microelectronic industry. SiC particulate reinforced aluminum MMCs satisfy these requirements. Using the Primex pressureless metal infiltration process, SiC loadings can be varied over a wide range, thus providing a family of composites with tailorable properties. The processing and properties, as well as the electronic applications of silicon carbide reinforced aluminum composites, are discussed.

• Microstructure and Properties of Metal Infiltrated Reaction-Bonded Silicon Nitride (RBSN) Composites, N.A. Travitzky and N. Claussen, J. Eur. Ceram. Soc., Vol 9 (No. 1), 1992, p 61-65. RBSN-metal composites were fabricated using gas-pressure infiltration. Various RBSN types have been infiltrated with molten aluminum, an Al-Si-Mg alloy, a Ti-Al intermetallic, and silicon, resulting in considerable increase in mechanical properties when compared to uninfiltrated RBSN. For example, strength was raised to 510 from

227 MPa when infiltrated with a Ti-39wt%Al alloy and the toughness to >5 from 2.7 MPavA^ when pure aluminum was infiltrated. Silicon infiltration proved to be most effective in enhancing the wear resistance.

• Low Shrinkage Refractories by an Infiltration Technique, N. Lequeux, P. Larose, P. Boch, and N. Burkarth, J. Eur. Ceram. Soc., Vol 14 (No. 1), 1994, p 23-27. Infiltration of presintered silica-zircon preforms with silica of alumina precursors and subsequent heating lead to the development of crystallized segregation (e.g., silica, alumina, or mullite), which decreases the sintering shrinkage. The decrease in shrinkage is very sensitive to the nature of segregations.

• Mechanical Properties of Al2O3/Si Composites Fabricated by Pressureless Infiltration Technique, N.A. Travitzky, E.Y. Gutmanas, and N. Claussen, Mater. Lett., Vol 33 (No. 1-2), 1997, p 47-50. A microstress-induced strengthening concept was applied to Al2O3/Si composites fabricated by pressureless infiltration of porous Al2O3 preforms with molten silicon. The mechanical properties (strength, hardness, fracture toughness) were superior to a material with the same amount of Al2O3 with aluminosilicate phase instead of silicon. For example, at 30% Si, the composite exhibits a bending strength of 320 MPa and K\c of 4.8

MPaV^ as compared to 230 MPa and 3.5 MPaV^, respectively, for a technical alumina AD-85. This strengthening is attributed to the compressive residual microstresses in an inherently weak silicon phase generated as a result of solidification-related expansion of silicon.

• Mullite/SiAlON/Alumina Composites by Infiltration Processing, M.P. Albano and A.N. Scian, J. Am. Ceram. Soc., Vol 80 (No. 1), Jan 1997, p 117-124. The formation of mullite/SiAlON/alumina composites was studied by infiltrating a SiAlON/alumina-base composite with two different solutions, followed by thermal treatment. The base composite was prepared from a mixture of Al2O3 grains, fume SiO2, and alumina powders. The mixture was pressed into test bars and nitrided in a nitrogen gas (N2) atmosphere at 1480 °C. The infiltrants were prehydrolyzed ethyl polysilicate solution and ethyl polysilicate-aluminum nitrate solution. The composites were infiltrated under vacuum, cured at 100 °C, and precalcined in air at 700 °C. This infiltration process was repeated several times to produce bars that had been subjected to multiple infiltrations, then the bars were calcined in a N2 atmosphere at 1480 °C to obtain mullite/SiAlON/alumina composites. The infiltration process increased the percentage of nitrogenous crystalline and mullite phases in the matrix; therefore, a decrease of the composite microporosity was observed. The infiltration increased the mechanical strength of the composites. Of the two composites, the one produced using prehydrolyzed ethyl polysilicate as the infiltrant had a higher mechanical strength, before and after being subjected to a severe thermal shock.

• Infiltration of Porous Aluminum Bodies with Solution Precursors, P. Honeyman-Colvin and F. Lange, Am. Ceram. Soc., Vol 79 (No. 7), July 1996, p 1810-1814. Alumina powder compacts, partially densified with a low-temperature heat treatment and then cut into bars, were infiltrated with liquid precursors that decomposed to either mullite (Al2O3, SiO2), fully stabilized zirconia (cubic Zr(8Y)O2), or partially stabilized zirconia (tetragonal Zr(4Y)O2). The specimens were repeatedly infiltrated and pyrolyzed to achieve a higher concentration of the precursor near the surface. The infiltrated bodies were then densified at 1500 °C for 2 h. Residual stresses developed during cooling from the densification temperature because of the higher concentration of the second phase near the surface and their differential thermal expansion relative to the matrix material. At least ten bars of each two-phase material were fractured in four-point bending to determine the effect of the second phase on strength. The alumina bars without a second phase had a larger grain size (=7 /'m) and a mean strength of 253 GPa. The intruded phases significantly reduced the A1203 grain size to =1 /'m. Despite their higher concentration near the surface and apparent surface tensile stress, both of the Zr(Y)O2 phases increased the mean strength to 413 MPa (cubic Zr(8Y)O2) and 583 MPa (tetragonal Zr(4Y)O2, an apparent toughening agent). The mullite second phase produced a high mean strength of 588 MPa, apparently due to its concentration gradient creating a compressive surface stress.

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