Sponsored by: Jt. SMD-MSD Composite Materials Committee
Program Organizer P.K. Liaw, Materials Science and Engineering Department, The University of Tennessee, Knoxville, TN, 37996-2200; R. Pitchumani, Mechanical Engineering Department, University of Connecticut, Storrs, CT 06269-3139; S.G. Fishman, Office of Naval Research, 800 N. Quincy Street, Arlington, VA 22217
Monday, PM Room: Marquis 1&2
February 5, 1996 Location: Anaheim Marriott Hotel
Session Chairperson: R. Pitchumani, Mechanical Engineering Department, University of Connecticut, Storrs, CT 06269-3139; R.F. Cooper, Depts. MS&E and NEEP, University of Wisconsin, Madison, WI 53706
HIGH-TEMPERATURE FLOW OF SiC CONTINUOUS FIBER-GLASS-CERAMIC MATRIX COMPOSITES: THE EFFECT OF INTERFACE/INTERPHASE DUCTILITY: B.G. Nair, J.N. Almquist, R.F. Cooper, M.E. Plesha, Depts. MS&E and NEEP, University of Wisconsin, Madison, WI 53706
The high-T rheology of continuous SiC-calcium aluminosilicate glass-ceramic matrix composites is evaluated in uniaxial compression creep experiments (-[[sigma]]1 = 20-to-40 MPa; T = 1300-1320deg.C). The steady-state strain rate is highly sensitive to the orientation of the reinforcement relative to the maximum compressional stress, with highest bulk specimen strain rates noted for conditions in which the sliding between the fiber and the matrix is optimized as a kinetic flow response, i.e., a fiber orientation of approximately 40-50deg. from [[sigma]]1. (These conditions produce far higher strain rates than when the fibers are perpendicular to [[sigma]]1). One further discovers that the temperature sensitivity of flow increases as the amount of interface flow/sliding increases. The experimental results suggest that the high-temperature, low-stress interface response in this composite system is related to the ductile flow of the "planar" SiO2 reaction-layer interphase that exists (in addition to the well-recognized planar carbon interphase) in these materials.
ELEVATED TEMPERATURE-VARIABLE-RATE MECHANICAL RESPONSE OF ALUMINA/FLUOROMICA LAMINATES: Todd T. King, Reid F. Cooper, Department of Materials Science and Engineering, University of Wisconsin, Madison, WI 53706
Elevated-temperature flexural delamination experiments are used to evaluate the mechanical performance of thermochemically and structurally stable [[alpha]]-alumina/thin-film fluoromica (Al2O3/KMg3[AlSi3]O10F2/Al2O3) laminates under the conditions T=25-800deg.C: =1x10-5 - 5x10-3s-1; air environment. At low T, the laminates display a purely brittle delamination response, one based on the intrinsic cleavage behavior of the mica. For T>400deg.C, a mixed, brittle-ductile interfacial response is noted, which is a clear function of strain rate: consistent with the physics of the brittle-ductile transition, more rapid rates allow for a brittle interfacial response (usually desired in a ceramic composite). The onset of thermally activated ductile deformation increases the energy for delamination. Microstructural analysis indicates both (partially anelastic) kinking and slip mechanisms are active in the mica interphase at high T. The results suggest that the mica can be engineered chemically so as to produce mechanically functional interfaces for alumina-fiber composites over a broad range of (T) conditions.
INFLUENCE OF SUBSTRATE ON THE ELASTIC REACTION OF FILMS FOR THE MICROINDENTATION TESTS: Youngman Kim, R & D Center, Korea Gas Corp. Ansan, Korea; Min-Tae Kim, KIA Motors, Seoul, Korea
The influence of substrate on the elastic reaction of thin film was investigated using a depth-sensing microhardness tester. Silicon oxide films were produced in a radio frequency (rf) plasma with hexamethyldisilane and oxygen, on <111> silicon wafers and glass ribbons simultaneously for the first set of samples and on <111> silicon wafers but with various film thickness for the second set. Young's moduli of the silcon oxide films were measured to be different for the different substrates for the same thickness of film. Young's moduli of the silicon oxide films decreased for the same substrate with increasing film thickness. The elastic deformation was considered for the normal point load to a flat quasi-infinite surface using an elementary theory of elasticity under the assumption of perfect adhesion between film and substrate.
PROPERTY-BASED OPTIMAL TAILORING OF COMPOSITE MATERIALS: D. Sadagopan, R. Pitchumani, Department of Mechanical Engineering, University of Connecticut, Storrs, CT 06269-3139
Composite materials offer designers the advantage of tailoring structures and materials to meet a variety of property and performance requirements in changing and demanding environments. However, the wide variety of materials combinations, reinforcement geometries and architectures to choose from, poses a bewildering problem of selections. Thus, an appropriate, and furthermore optimal, tailoring of materials for composites applications is a challenging design problem and forms the focus of the paper. Specifically, the present work addresses the problem of selecting optimal combinations of matrix and reinforcement materials, reinforcement morphology, architecture, and volume fraction so as to meet specified property and performance requirements. Matrix materials considered in the study span the material classes of polymers, metals and ceramics, while reinforcement geometries considered include continuous fibers, particulates and short fibers, and two-dimensional textile fabrics. Analytical models available in the literature are used to relate the composite properties to their microstructures. The property model base, in conjunction with the combinatorial optimization technique of simulated annealing, is used to solve the optimal materials tailoring problem. The overall approach and key results of the study will be presented and discussed.
EFFECTS OF NEUTRON IRRADIATION ON THERMAL EXPANSION OF SiCf/SiC COMPOSITES: D.J. Senor, Pacific Northwest Laboratory, Richland, WA 99352; D.J. Trimble, Westinghouse Handord Company, J.J. Woods, Lockheed-Martin, Schenectady, NY 12301
The effect of irradiation on thermal expansion of several SiCf/SiC composite types was studied. Thermal expansion was measured using an alumina pushrod dilatometer between room temperature and 1000deg.C. The irradiated specimens were subjected to a neutron dose of either 33 or 43 dpa-SiC in the Experimental Breeder Reactor-11 at approximately 1000deg.C. The composites possessed a variety of constituent materials including two matrix types (CVI SiC and liquid infiltrated polymer-precursor SiC), three fiber types (Nicalon, Tyranno, and HPZ), and two interface types (pyrolytic carbon and boron nitride). In the unirradiated condition, thermal expansion was primarily dependent on the matrix material. The presence of the fibers resulted in a contribution to the unirradiated thermal expansion only for highly anisotropic fiber architectures. After irradiation, the fibers were observed to have completely debonded from the matrix, resulting in thermal expansion behavior that was solely dependent on the matrix type.
INFLUENCE OF FIBRE NETWORK INTERCONNECTION ON THE THERMAL EXPANSION ANISOTROPY IN METALLIC COMPOSITES: L. Tao, F. Dolannay, Université catholique de Lonvain, Département des sciences des matériaux ei des procédés, PCIM, Place Sainte Barbe 2, B-1348 Louvain-la-Neuve, Belgium
Transverse isotropic fibre networks were prepared by pressing mats of steel fibers and sintering under protective atmosphere. The number and strength of the bonds at fibre interconnections varied as a function of sintering conditions, fibre volume fractions, and fibre cross-sections. These networks were used as preforms for creep strengthening Zn-Al foundry alloys. The composites were processed by squeeze casting. They presented widely different thermal expansion coefficents in the directions parallel and perpendicular to the plane of the preform. The magnitude of the anisotropy was found to depend on the degree of fibre interconnection in the network. Reversibility of the strains during thermal cycling up to 180deg.C suggested no plastic yielding of the matrix. A model is developed for accounting for this behavior.
FABRICATION OF SILVER-Al2O3p ELECTRICAL CONTACT BY ELECTROLESS PLATING AND HOT PRESSING: Jiunn-Horng Lin, Su-Jien Lin, Dept of Matls Sci & Engrg, National Tsing Hua University, Hsinchu, Taiwan, China
In this research, Al2O3p reinforced silver matrix composites with different
amounts of reinforcements, 10, 20 and 40 vol. % and different partical size, 3
um and 1 um, were fabricated by electroless silver plating followed by cold
compacting and hot pressing at 500[[ring]]C or 600[[ring]]C, 300 MPa in air.
The distributions of the Al2O3p were rather uniform. Densification was obtained
by comparing the true densities of the composites measured by Archimedes' law
with the theoretical densities calculated from ICP-AES analysis. Density
measurement confirmed that the composites can be fully densified. Hardness and
bending properties of the composites were also tested and found to be much
better than pure silver. Electrical conductivity were measured by four-point
probe method and revealed that the silver-Al2O3p composites have a higher
electrical conductivity than the traditional silver CdO electrical contact.
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