Mr. Mark R. van den Bergh
President, DWA Aluminum Composites
21130 Superior Street
Tel: (818) 998-1504
Fax :(818) 998-0343
E-mail: mvdb@aol.com

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Discontinuously reinforced titanium (DRTi) matrix composites offer higher specific modulus, specific strength, wear resistance and thermal stability as compared to the unreinforced titanium alloys. The blended elemental (BE) powder metallurgy approach allows more control of alloy microstructure and a wider range of reinforcement volume percentage than conventional casting techniques or prealloyed powder techniques. Typically, morphology, not volume percentage, of the reinforcement phase is limited by the phase diagram for casting approaches. Hypereutectic compositions with primary titanium boride (TiB) particles are likely to have poor fatigue properties. Needle morphology, better for strength and fatigue, can most likely be obtained for hypereutectic compositions only by in-situ reaction with titanium diboride (TiB2). In this study two alloys were selected for investigation; DRTi-6Al-4V and DRTi-10V-2Fe-3Al, both reinforced with 15 volume percent TiB. The composites were produced via the blended elemental powder metallurgy technique and extruded to obtain a fully dense material. The composites were also produced using hot isostatic pressing (HIP) to compare with the extruded material. The particulate reinforcement was obtained through the in-situ synthesis of TiB from TiB2. Samples of the extruded materials and HIP materials where then heat-treated and microstructural characterization was performed to evaluate the reinforcement phase formation. The TiB evolution and transformation kinetics will be discussed.

This work was performed at the Materials and Manufacturing Directorate, Air Force Research Laboratory. Wright-Patterson AFB, OH.

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After more than 20 years of development, discontinuously reinforced metals have now achieved application in the aerospace, electronics and transportation industries . Despite this level of maturity, the scope of application of discontinuously reinforced metals is limited by low ductility and fracture toughness. While it is generally acknowledged that the composite particle distribution must be improved to improve these properties, a widely accepted means of quantifying particle distribution does not yet exist. The results of a novel, multi-scale microstructural characterization of the particle distributions based on complex systems analysis will be presented and related to the composite mechanical behavior. This technique represents a significant departure from previous methods, which rely on averaged particle local environments, and do not capture particle clustering on multiple length scales.

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MMC’s, metal matrix composites, discontinuously reinforced composites, particle distribution, complex systems analysis, fractals, multi-scale, image analysis, microstructure characterization.

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Aluminum matrix alloys in SiC and Al2O3 particulate reinforced MMC's with high ceramic particulate volume fraction were optimized for high ultimate tensile strength and fracture toughness. A wide spectrum of alloys was tested as a candidate matrix and as a result large database of composite properties was created. Successful strategy for matrix alloying in SiC and alumina reinforced composites is discussed in application to pressure infiltration manufacturing technology. Effects of matrix alloy composition on mechanical properties of composites are explained using results of microstructure and fracture mechanisms studies carried out in the work.

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A.B. Pandey, B.S. Majumdar, and D.B. Miracle

Materials and Manufacturing Directorate
Air Force Research Laboratory, AFRL/MLLM,
Wright-Patterson AFB, OH 45433

UES, Inc.
4401 Dayton-Xenia Road
Dayton, OH 45432

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DRA composites have received considerable attention in the recent years due to their superior specific stiffness, specific strength, wear resistance, and thermal resistance as compared to the unreinforced aluminum alloys. However, DRAs have lower ductility and fracture toughness than the base alloys, and these are the key issues in the application of these materials in aerospace structures. In this study, SiC particle reinforced aluminum alloy composites produced using a powder metallurgy technique were considered. Tensile and fracture toughness, JIc, tests were performed in different microstructural conditions. The effect of heat treatment, particle size, volume fraction, and matrix alloy on the ductility and toughness of the composites were evaluated. The ductility and fracture toughness varied inversely as the strength, being the highest in the solution-treated and highly-overaged conditions, and lowest in the peak-aged condition. In all the heat treatment conditions, damage was present in the form of particle fracture and interface debonding, with the peak-aged material exhibiting damage and associated plasticity in a very small fraction of the gage length. While there was a considerable effect of particle size on the strength and ductility of the composite, the toughness was almost independent of the particle size within the limited size range considered. These are discussed in the context of damage in tensile specimens, as well as in the highly constrained region ahead of the crack tip.

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A new metal matrix/ carbon fiber composite has been fabricated. The new material is 50 to 60 volume percent continuous carbon fiber in a nickel alumide matrix. The composite exhibits the high strength and modulus of the carbon fiber while the matrix is essentially a superalloy, which maintains its properties to high temperatures. The carbon fiber is shown not to react with the matrix even though the composite was formed at high temperature, this being due to the thermodynamically stable nature of the nickel alumide matrix with respect to carbon. The uniform nickel and aluminum distribution in the matrix is obtained by coating each carbon fiber with nickel and aluminum by a chemical vapor deposition process, then subsequently hot pressing the coated fibers at high temperature to the desired shape.

The method of manufacture of this new material will be described. The physical properties of the material will be shown as a function of temperature and compared to other aerospace materials. In the temperature range of 400 to 600 degrees Celsius, the new material can be seen to have approximately twice the specific strength of other aerospace materials.