Tuesday, PM Room: B4
February 6, 1996 Location: Anaheim Convention Center
ON ELASTOPLASTIC RESPONSE OF PARTICULATE-REINFORCED METAL-MATRIX COMPOSITES UNDER MULTI-AXIAL LOADINGS: M.V.S. Ravisankar, Department of Mechanical and Aerospace Engineering and Engineering Science, N. Yu, P.K. Liaw, Department of Materials Science and Engineering, The Univ. of Tennessee, Knoxville, TN 37996
A micromechanics model based on periodic microstructure is developed to predict the overall elastoplastic response of and to examine the microstructure-property interactions in particulate-reinforced metal-matrix composites (MMCs) under multi-axial loadings. The model explicitly accounts for not only the material properties of the matrix and the particulates but also vital microstructural parameters, such as the shape, size and packing density of the particles. Analytic solutions of the average stress and strain increments in the MMCs are obtained by using homogenization techniques along with Fourier series(1). The elastoplastic behavior predicted by the present model are compared with the uniaxial tensile testing results of silicon carbide particulate reinforced (SiCp) aluminum (Al) matrix composites, fabricated by a powder metallurgy extrusion process. The effects of particle volume fraction (0~30~%), matrix properties (2124, 6061 and 7091 Al), and particle aspect ratio on the effective elastoplastic response of Al/SiCp composites are also studied.
THE DUCTILITY OF METAL MATRIX COMPOSITES UNDER TRANSVERSE LOADING CONDITIONS: Leon L. Shaw, Department of Metallurgy and Institute of Materials Science, University of Connecticut, Storrs, CT 06269
Continuous-fiber reinforced titanium alloys exhibit superior properties along the fiber axis. However, the transverse properties of these composites have been shown to be lower than desired for some applications. In this study, an effort is made to develop an understanding of the dependencies of the composite ductility on the matrix ductility and the fiber/matrix bond strength under transverse loading conditions. Localized ductility around the fiber was evaluated through a laser interferometer, and compared with the overall ductility of the composites under the transverse loading. Numerical modeling (elastic/plastic) was also carried out to extend the experimental results to accommodate composites with different matrix ductilities and interfacial properties. The experimental and modeling results will be presented and the approaches to improving the transverse ductility of the composites will be proposed.
MECHANICAL BEHAVIOR OF AN Al-6092 ALLOY REINFORCED WITH 17.5 VOLUME PER CENT OF SiC PARTICULATES: Kedarnath Poduri, Yan Ma, Terence G. Langdon (Departments of Materials Science & Mechanical Engineering, University of Southern California, Los Angeles, CA 90089-1453)
Experiments were conducted to evaluate the mechanical characteristics of an Al-6092 metal matrix composite containing 17.5 vol % of SiC particulates. Creep and tensile tests were performed in air at temperatures in the range from 723 to 823 K. Maximum tensile elongations in excess of 100% were recorded at the lower testing temperatures when using very high strain rates. This paper describes the results of these experiments, including the values of the stress exponent and the activation energy.
HIGH-TEMPERATURE DEFORMATION OF A SiC--2124 Al COMPOSITE AND 2124 Al: Yong Li, Farghalli A. Mohamed, Materials Science and Engineering, Dept. of Chemical and Biochemical Engilleering University of California, Irvine, CA 92717
The effect of stress and temperature on the high-temperature deformation of S vol.% silicon carbide particulate reinforced 2124 Al (SiCp-2124 Al), produced by powder metallurgy, has been studied. The experimental data of the composite are examined in reference to those of the matrix alloy, 2124 Al, that was tested under similar experimental conditions.
3:20 pm BREAK
CREEP IN SiC-REINFORCED P/M 6061 ALUMINIUM COMPOSITE: S. L. I. Chan, J. L. Hwang, Institute of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan, 100 China
The mechanical behaviour of P/M 6061 aluminium matrix composite at elevated temperatures (350-450°C) has been studied. These composites contained 0 to 20% of SiC reinforcements of different sizes. The results show that for the monolithic 6061 Al alloy, the solutes in the alloy impinged the movement of dislocations, consequently the first stage of creep was absent or reduced. A threshold stress was found for the onset of creep, but this threshold stress diminished as the temperature increased. With the addition of SiC reinforcement, the resistance of the material to creep was improved, and the activation energy for creep and stress exponent increased correspondingly. However, no threshold stress was detected in the composites. In contrast to the monolithic specimens, all three stages of creep were found for the composites, but the extent of steady creep (Stage II) was reduced by the increasing amount of ceramic reinforcement.
THERMOMECHANICAL FATIGUE OF A METAL MATRIX COMPOSlTE: D. R. Lesuer, C. K. Syn, T.G. Nieh, L-342,Lawrence Livermore National Laboratory, Livermore, CA 94551
The thermo mechanical fatigue (IMF) behavior of a discontinuously reinforced aluminum (6090/SiC/25p) has been studied over the temperature range of 25-450°C. TMF can occur in metal matrix composites because of the internal stresses produced during thermal cycling. These stresses result from the thermal expansion mismatch between matrix and reinforcement. It is well established that during temperature cycling these internal stresses can produce local plastic flow near the interface of the matnx and reinforcement. Damage can also result that leads to failure. In this study we have evaluated the influence of cyclic mechanical loading and thermal loading on fatigue life. The work reported here was conducted with a unique experimental apparatus that permits independent control over both the thermal and the mechanical loading histories applied to the sample. This presentation will describe the results of these studies including the influence of cycling temperature and cycling thermal frequency. The origins of fracture will be described and possible mechanisms discussed. This work was performed under the auspices of the U.S. Department of Energy by LLNL under contract No. W-7405- Eng- 48.
THE COMBINED EFFECT OF SOLUTIONIZING TIME AND VOLUME FRACTION OF PARTICLES ON THE AGING CURVES AND MICROSTRUCTURES IN A COMPOSITE WITH 6061 ALLOY MATRIX REINFORCED WITH Al2O3 PARTICLES: Javier Ponce, Daniel Salas, Michael Solis, Shane Andrews, S. K. Varma, Department of Metallurgical and Materials Engineering, The University of Texas at El Paso, El Paso, TX 79968-0520
The composites with 6061 aluminum alloy matrix and 0.10, 0.15 and 0.20 volume fractions of Al2O3 particles have been solutionized at 540°C for different times up to 20 hours to produce various grain sizes after quenching. The aging response of these solutionized composites have been examined with the help of microstructural evolution and aging curves. The relationship between the grain size developed during the solutionization process by grain growth and volume fraction of the particles on the aging curves has been investigated. The influence of CTE dislocations on the precipitation sequence and peak hardness values will be compared with the behavior of 6061 aluminum alloy in its monolithic form under identical experimental conditions. This research has been supported by the National Science Foundation through the grant number HRD-9353547.
LASER BEAM PROCESSING OF PARTICULATE REINFORCED 6061 ALUMINIUM METAL METRIX COMPOSITE: Li Hong, Laser Lab, Department of Materials, Institute Superior Tecnico Av. Revisco Pais, 1096 Lisbon, Portugal; Wang Youming, Department of Metal Forming, University of Science & Technology Beijing, Beijing 100083, China
SiC/Al203 particulate reinforced 6061 Al metal matrix composites were laser beam cut and welded using a 3kw continuous wave C02 laser. The influence of of laser processing parameters such as cutting/welding speed, laser power, and shielding gas rate on the quality of cuts and welds were investigated. Optical microscopy, scanning electron microscopy and x-ray diffraction were used to analyze the laser treated zone. Experimental results had shown that 6061 Al MMCs can successfully laser cut and weld. The Al4C3 plates were formed in HAZ due to the chemical reaction between Si and Al ocurring during laser processing.
MICROSTRUCTURE AND PROPERTIES OF A SiC FIBER-REINFORCED "ORTHORHOMBIC" TITANIUM ALUMINIDE COMPOSITE PRODUCED BY PHYSICAL VAPOR DEPOSITION: S. Krishnamurthv, P. R. Subramanian, A. McCormick, UES, Inc., Dayton, OH 45432
Several methods are currently available for fabricating fiber reinforced titanium matrix composites which are candidate materials for structural aerospace applications at moderately high temperatures. The present work deals with the processing of a SiC fiber reinforced "orthorhombic" titanium aluminide composite using physical vapor deposition (PVD). The PVD process consisted of magnetron sputtering of a Ti3Al-Nb alloy matrix on SCS-6 SiC fibers. The matrix-coated fibers were consolidated by hot pressing to form a unidirectionally reinforced composite containing about 35 vol.% fibers. Unreinforced matrix alloy samples were also fabricated using identical sputtering and consolidation conditions. The microstructural changes in these materials following different heat treatments was studied. Preliminary tensile tests were also conducted on matrix and composite specimens at room temperature. The microstructures of all the specimens were characterized by optical microscopy, SEM, electron microprobe, and x-ray diffraction techniques. The results of microstructural charactelization and tensile testing of these PVD processed matelials will be discussed. This research was performed under AF Contract F33615-94-C-5214.
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