Sponsored by: EPD Process Fundamentals Committee, MSD Thermodynamics & Phase Equilibria Committee, Japan Institute of Metals
Program Organizers: Prof. R.Y. Lin, University of Cincinnati; Prof. Y. Austin Chang, University of Wisconsin-Madison; Prof. R. Reddy, University of Navada-Reno and Dr. C.T. Liu, Oak Ridge NL
Monday, AM Room: B2
February 5, 1996 Location: Anaheim Convention Center
Session Chairperson: Ray Y. Lin, Dept. Materials Sci. & Eng., University of Cincinnati, M.L. #12, Cincinnati, OH 45221-0012; Li Lu, Dept. Mech. & Production Engineering, The National University of Singapore, 10 Kent Ridge Crescent, Singapore OSIII
8:30 am Keynote Address
IN-SITU COMPOSITE SYNTHESIS OF METAL SILICIDE REINFORCED WITH SILICON CARBIDE VIA SOLID STATE DISPLACEMENT REACTIONS: C. R. Kao, Y. A. Chang, Department of Material Science and Engineering, University of Wisconsin, Madison, WI 53706
The principle of thermodynamics and kinetics which governs solid-state displacement reactions to synthesis structural composites in-situ will be briefly described. Application of these principles will be illustrated using experiments being carried out at Madison to synthesize NbSi2/SiC composite by reacting NbC powder compact with Si single crystal. Diffusion couple experiments consisting NbC/Si are being carried out at 1300=B0C for times=up to 100h. The resulting microstructure is a layer of continuos NbSi2 matrix dispersed with SiC particle with an average size of 1mm. The rationale for occurrence of this type of microstructure is discussed as well as our proposed reaction mechanism. Growth of the reaction layer involves long-range diffusion of Si through this layer and short-range diffusion of Nb and C around the reaction front. The particles sizes of SiC appear to be controlled by the voids in the NbC powder compact.
9:00 am Invited
CRITERIA FOR MATRIX SELECTION IN CONTINUOUS FIBER ALUMINUM MATRIX COMPOSITES: Colin McCullough, 3M Company, MMC Program, St. Paul, MN 55144
Traditionally Continuous Fiber Aluminum Matrix Composites have been fabricated using high strength fibers and high strength matrices, often commercial alloys, with the goal of producing high strength composites. However the specific role of the matrix on all areas of composite performance have not been well established. One way to control composite properties, which will be shown, is to use coatings to introduce a low strength interface between fiber and matrix which tends to reduce the importance of the matrix selection, but unfortunately renders the transverse strength unacceptably low. Thus using a system with strong bonding between fiber and matrix is desirable, such as an alumina fiber/aluminum alloy matrix system. In this case the transverse strength is a strong function of the matrix strength. However the longitudinal strength then depends largely on the characteristics of the matrix. The important role of the matrix will be discussed using examples of alumina fibers in various aluminum alloy matrices. The key attributes are matrix constituent phases, alloy chemistry,alloy reactivity with the fiber and matrix strength. From the understanding developed in these systems a set of design rules may be established for selecting an optimum matrix.
9:25 am Invited
SYNTHESIS AND CHARACTERIZATION OF LOW SILICA MoSi2 COMPOSITES USING IN-SITU DISPLACEMENT REACTIONS: M. J. Kaufman, A. Costa e Silva, S. Jayashanar, M.J. Kaufman, Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611
Previously, we have shown that MoSi2-matrix composites can be synthesized using in-situ displacement reactions involving carbon (to form SiC) and aluminum (to form Al203) additions. These reactions lead to the simultaneous reduction and elimination of silica from the micro-structures. In the present study, we have extended these efforts to produce MoSi2-boride (MoB, Mo2Bs and TiB2) composites using a combination of the lower silicides and boron. For the boride-reinforced materials, the resulting microstructures are fine scale and consist of interpenetrating silicide and boride phases. In this presentation the microstructural evolution in these composites will be. Our characterization of the mechanical properties of the low-silica material indicate that both silica and grain size are extremely important in determining the mechanical properties of these composites and that careful control of the processing strategies allow what appears to be superplastic deformation at small grain sizes and relatively high creep strengths at larger grain sizes. This work was supported by the Office of Naval Research, Grant No. N00014-91-J4132, under the direction of Dr. Steve Fishman.
IDENTIFICATION OF THE INTERFACE FAILURE MECHANISM DURING TRANSVERSE LOADING OF SCS-6/Ti-6Al-4V COMPOSITES: Sunil G. Warrier, Systran Corporation, Dayton, OH; Bhaskar S. Majumdar,UES, Inc., Dayton, OH; Daniel B. Miracle, Materials Directorate, Air Force Wright Laboratory, Wright-Patterson Air Force Base, Dayton, OH 45433
During transverse testing of continuous fiber-reinforced composites, along with the increase in the normal stress parallel to the loading axis, large tangential shear stresses develop at the interface at about 45deg. to the loading axis. Depending on the properties of the interface, these shear stresses may initiate interface failure. Once frictional sliding has initiated, either the interface can lose a part of its load carrying capacity or lower the normal strength of the interface. It is therefore necessary to establish a fundamental understanding of the governing interface failure mechanism in these composites. In order to clearly quantify the tangential shear strength of the interface, shear stresses have to be isolated from mechanically induced normal stresses. In the present study, the interface has been subjected to pure shear stresses through torsion testing. Result indicate that in SCS6/Tl-6Al-4V composites shear failure is likely to have preceded normal failure of the interface during transverse loading. Detailed evaluation of the micro-mechanical aspects of the interface response to torsion testing will be presented.
10:15 am BREAK
10:25 am Invited
PERFORMANCE OF BARRIER COATINGS FOR AL2O3 FIBERS IN TITANIUM ALLOYS: Rob Kieschke, J.R. Heffelfinger, C.B. Carter, 3M Company, MMC Program, St.Paul, MN 55144
Abstract not available.
KINETICS OF INTERFACIAL REACTION IN COMPOSITES: Al/Inconel Inconel 601. A. V. Ruzette, F. Boland, A. Colin, F. Delannay, Universite catholique de Louvain, Departement des sciences des materiaux et des procedes, PCIM Place Sainte Barbe, PCIM Place Sainte Barbe; 2, B-1348 Louvain-la-Neuve, Belgium
Reinforcement of Al-base alloys with continuos Inconel 601 fibers is studied as a means for enhancing high temperature properties. The volume fraction of the fibers was varied between twenty and sixty volume percent. The composites were processed by squeeze casting. Adequate ductility requires that the extent of interfacial reaction be minimized. A low thermal inertia squeeze casting set up was designed in order to achieve rapid solidification of the metal after infiltration of the preform. The severity of reaction was controlled by varying the preheating temperature of the mold and of the fiber preform and the mass and temperature of the liquid metal cast in the mold. The influence of these parameters was monitored by measuring the temperature evolution from the moment of infiltration. The nature and amount of reaction compounds was characterized by EPMA and image analysis. The reaction kinetics was modeled assuming a parabolic law. The influence of fiber heat treatment, fiber volume fraction, and silicon content of the matrix alloy on reactivity was also elucidated.
11:15 am Invited
INTERFACIAL CHARACTERISTICS OF SQUEEZE-CAST SiC-REINFORCED AZ91D MAGNESIUM-BASED COMPOSITES: Jason Lo, Graham Carpenter, MTL/CANMET, Department of Natural Resources Canada, 568 Booth St., Ottawa, Ontario K1A0G1, Canada
The method of producing magnesium-based composites with silicon carbide (SiC) particulates embedded in the matrix of magnesium AZ91D alloy by the squeeze casting technique are described. This method involves the fabrication of a SiC particulate preform and the subsequent squeezing of molten magnesium into the preform. In this study, alumina, phosphate and aproprietary binder were used for the fabrication of SiC particulate preforms. The procedures employed in the fabrication of SiC/AZ91D composites are presented, together with the results of characterization of the composites using scanning and transmission electron microscopy. Special attention is given to the reaction products in the bulk alloy and at the interfaces between SiC particles and the AZ91D matrix alloy especially when different binders were employed. The significance of the presence of some reaction products in relation to their effects on mechanical properties are discussed.
11:40 am Invited
THERMAL CYCLING OF AL2O3 FIBER-REINFORCED SUPERALLOY COMPOSITES: Gopal Das, Robert J. Miller, D. Wheeler, Pratt & Whitney, P. O. Box 109600, W. Palm Beach, FL 33410-9600
The coefficient of thermal expansion (CTE) mismatch between the fiber and
matrix is known to cause damage in a composite following thermal cycling, the
severity of which intensifies with increasing CTE mismatch. Two superalloy
matrix, HA 214 and MA 956 with significantly different CTE were
unidirectionally reinforced with single crystal A1203 fibers (Saphicon) and
subjected to thermal cycling between room temperature and 1800 F in air. The
Saphicon/HA 214 composite bar started to exhibit bending after 50 cycles while
the Saphicon/MA956 composite showed negligible bending after 400 cycles.
Thermal cycling in air was accompanied by a substantial weight gain (1.77%) in
Saphicon/HA 214 composite and a negligible weight gain (0.197%) in
Saphicon/MA956 composite after 400 cycles. Microstructural characterization of
thermally cycled Saphicon/HA 214 composite bar revealed twinning in fibers and
with increasing cyclic exposure all these fibers appeared cracked. In contrast,
fibers in Saphicon/MA 956 composite did not reveal any twinning or cracking.
The presence of both oxides and nitrides were detected in the fiber/matrix
interface of thermally cycled composites by a combination of x-ray, SEM and
electron microprobe studies. The observation of twinning and cracks in fibers
will be discussed in terms of residual stresses developed during cooling and
heating of the composite.
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