Program Organizer: P.W. Keefe, Special Metals Corporation, New Hartford, NY 13413, M. Sohi, Allied Signal Engines, Phoenix, AZ 85072-2118
Tuesday, AM Room: B4
February 6, 1996 Location: Anaheim Convention Center
Session Chairperson: P.W. Keefe, Special Metals Corporation, New Hartford, NY 13413
RECENT ADVANCES IN FIBER COATING TECHNOLOGY FOR USE IN SiC/Ti-MMCs: D. Upadhyaya, Institute for Materials and Advanced Processes, University of Idaho, Moscow, ID 83844-3026; M. J. Wood, C. M. Ward-Close, Structural Materials Centre, DRA Farnborough, Hants, GU14-6TD, UK; P. Tsakiropoulos, Department of Materials Science and Engineering, University of Surrey, Guildford, Surrey, GU2 5XH,UK; F. H. Froesa, Institute for Materials and Advanced Processes, University of Idaho, Moscow, ID 83844-3026
Continuous silicon carbide fiber-reinforced titanium-based metal matrix composites offer many advantages over conventional monolithic materials including high strength-to-density ratio. However, there is a need to design an improved protective coating for the silicon carbide fiber to combat interfacial chemical reactions as well as to accommodate large mismatch in the coefficient of thermal expansion (CTE) between the SiC fiber and titanium matrix. This paper describe the strategy for designing coatings for continuous silicon carbide fiber and reports on a new coating system based on a compliant layer/reaction barrier concept developed for titanium metal matrix composites including those based on [[gamma]]-TiAl. The newly developed coating system, designated FUWT, consists of Gd/GdB3 where the Gd layer (adjacent to SiC) works as a compliant layer while the GdB3 layer works as a reaction barrier. The results of this work indicate that the FUWT coating perform well both as a reaction barrier (protect the SiC fiber from reactions with titanium up to 1100C) and a compliant layer (absence of thermal cracking in TiAl based composite). The interfacial shear strength of an as-fabricated SiC/FUWT/Ti-6Al-4V was found to be higher than the presently available SCS6/Ti-6Al-4V and Sigma (SM1240)/Ti-6Al-4V composites.
SiC FIBER STRENGTH BEFORE AND AFTER CONSOLIDATION IN A Ti-ALLOY MATRIX COMPOSITE: M. L. Gambone, Materials Directorate, Wright Laboratory, Wright-Patterson AFB, OH 45433; V. Fry, Amercom, ARC Sequa Corporation, Chatsworth, CA 91311
The strength distribution of three spools of SiC fiber was measured before fabrication in Ti-22Al-23Nb (atomic percent) matrix composite panels. Fibers were then extracted from the composite and tensile tested to measure the post-consolidation strength distribution. The tensile properties of each fiber spool tested before and after composite processing were compared. Fibers from the spool which showed the best pre-consolidation strength demonstrated little loss of strength after extraction from the matrix; however, indications of low strength fiber in the pre-consolidation tensile data were mirrored in the extracted strength distributions. Fractography of extracted fibers indicated tensile failure initiated from the core, mid-radius, and surface of fibers. The relative strength of failures initiating from each location will be discussed as well as their impact on the overall fiber strength distribution.
THE INDENTATION SHEAR STRENGTH OF SCS-8/7075 AL COMPOSITES: Liang-Guang Chen, Su-Jien Lin, Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan, China
Push-out tests were conducted to determine the interfacial shear strengths of SCS-8/7075 Al composites prepared using diffusion bonding process. The effects of strengths of matrix after aging and annealing treatment on the debonding behavior were studied. The interfacial shear strength of the peak-aged composite was found to be higher than those of the under-aged and over-aged composites. Due to the low strength of the matrix after annealing treatment relative to the interfacial strength, the premature fracture of the SCS-8 fiber occurred and resulted in a lower interfacial shear strength during the test. The interfacial shear strengths were also variant for the different SCS-8 fibers of a specimen because the extent of matrix plastic flow during hot-pressing was not the same.
THE DEVELOPMENT OF MONOLITHIC AND GRADED CERAMIC/INTERMETALLIC COMPOSITES BY TAPE CASTING AND REACTIVE INFILTRATION: S. F. Corbin, P.S. Apté, Sherritt Inc. Fort Saskatchewan, Alberta, Canada T8L 2P2
Intermetallic and ceramic materials are candidates for a number of applications including high temperature oxidation-resistant structural materials for aerospace and turbine service. The fabrication of composites from these two class of material allows one to tailor the properties of a part to suit the desired application. This is particularly true if a manufacturing process can be developed where a functionally graded component can be produced with controlled composition and microstructural architecture. This paper will describe the development of a process whereby monolithic and functionally graded ceramic/intermetallic components are formed using a tape casting/reactive infiltration route. Development of tape casting formulations and debindering/sintering techniques will be described which result in the formation of ceramic/metal preforms with both graded composition and porosity. In addition, the reactive infiltration of these preforms to form intermetallic/ceramic composites will be described. The dependence of the microstructural characteristics of these composites on the preform microstructure (i.e. porosity and ceramic/metal composition) and infiltrating conditions (i.e. time and temperature) will also be described.
9:50 am BREAK
ON THE PERFORMANCE OF TITANIUM BASED HYDROGEN STORAGE ALLOY ELECTRODE WITH ALUMINIUM ADDITION: B. Luan, N. Cui, H. J. Zhao, S. Zhong, H. K. Liu, S. X. Dou, Centre for Superconducting & Electronic Materials, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522 Australia
Effects of aluminium addition on the performance to Ti2Ni hydrogen storage alloy electrode have been studied in the present work. The cycle life of the electrode was found greatly increased with aluminium addition. XRD (X-Ray Diffraction) analysis indicated the co-existence of a new phase, Ti2Al, with Ti2Ni. Electrochemical studies revealed that the electrode with aluminium additions are characterized of having active-to-passive transition. The reason for this was attributed to the passivation of the new Ti2Al phase. The passive film was confirmed to be composed of titanium and aluminium by AES (Auger Electron Spectroscopy) analysis. Passivation of the electrode reduce the oxidation of alloy powder during charge-discharge process and therefore increase the cycle life of the titanium based hydrogen storage alloy electrode.
ELECTRODE PERFORMANCE OF Mg2Ni-10wt.%Ti2Ni COMPOSITE ALLOY: N. Cui, B. Luan, H. J. Zhao, S. Zhong, H. K. Liu, S. X. Dou, Centre for Superconducting and Electronic Materials, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522 Australia
Mg2Ni-10wt.%Ti2Ni sintered composite alloy has been successfully synthesized.
The performance of the electrode fabricated from this alloy has been
investigated for the first time. X-ray diffraction results showed that
Mg2Ni-10wt.%Ti2Ni sintered composite alloy composed of Mg2Ni, Ti2Ni and TiNi.
Composite of Mg2Ni with Ti2Ni greatly increased the discharge capacity of the
Mg2Ni-type alloy electrode. The discharge capacity of the electrode was
increased from 8 mAh/g for Mg2Ni electrode to 126 mAh/g at ambient temperature.
This may be attributed to the co-existence of Ti2Ni and TiNi with Mg2Ni alloy
which enhanced the hydrogen reaction electrocatalytic activity of Mg2Ni alloy,
resulting in the improvement of the hydriding-dehydring kinetics.
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