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Session Chairpersons: F.H. (Sam) Froes, University of Idaho, Institute for Advanced Processes, Mines Bldg 204, Moscow, ID 83844-3026; D. Chellman, Lockheed Aeronautical Systems Co., Lockheed Corporation, Marietta, GA 30063-0150
RECENT ADVANCES IN THE SYNTHESIS OF LIGHT WEIGHT METALLIC MATERIALS: C.M. Ward-Close, F.H. Froes, and S.S. Cho, Chief Metal Matrix Composites, Structural Materials Centre, DRA Farnborough, Hampshire GU14 6TD, UK; Director IMAP, University of Idaho, Moscow, Idaho 83844-3026; Lockheed Technical Fellow, Advanced Structures and Materials, Lockheed Aeronautical Systems Co., Marietta, Gorgia 30063; Vice Director of RASOM, Rapidly Solidified Materials Research Center, Chungnam National University, Taedok Science Town, Taijon 305-764, Korea
Recent advances in the synthesis of light-weight metallic materials will be reviewed with emphasis on developments which have occurred since the last symposium in this series. Primary consideration will be given to alloys based on aluminium, magnesium and titanium both in monolithic and composite configurations. Emphasis will be on synthesis/processing/fabrication rather than the more traditional microstructure-mechanical property relationships. Particular attention will be given to the status of commercialisation of high performance light-weight metallic materials.
HYDROGEN STORAGE WITH MAGNESIUM-IRON NANOCOMPOSITES: M.A. Imam, Materials Science and Technology Division, Code 6323, US Naval Research Laboratory, Washington, DC 20375; R.L. Holtz, Geo-Centers, Inc., 10903 Indian Head Highway, Fort Washington, MD 20744
Of potential practical hydrogen storage materials (HSM), pure Mg would be best from the standpoint of hydrogen capacity per unit mass. However, pure Mg has poor hydrating reactivity due to surface oxide poisoning and low catalytic activity. Mg-Ni is a well-known attentive that is more stable against oxidation. The Ni aids catalysis of the H2 dissociate chemisorption and produces additional benefits by lowering the dehydrogenation temperature, but at the expense of a decrease in storage capacity. Theoretical considerations suggest that nanostructured Mg with low concentrations of both Ni and Fe will be an optimum Mg-based HSM. We have prepared submicron Mg-(Ni,Fe) pseudoalloys by bail milling and report here on the hydrogen storage characteristics.
PROCESSING AND PROPERTIES OF TITANIUM AND TITANIUM METAL MATRIX COMPOSITE BASED LAMINATES: Y.Q. Zuo, D.J. Smith, P.G. Partridge, A. Wisbey; Department of Mechanical Engineering, Interface Analysis Centre, University of Bristol, UK; Structural Materials Centre, DRA Farnborough, UK
Two laminate systems based on titanium alloy IMI834 and titanium metal matrix composite (MMC) have been manufactured by diffusion bonding. The S-type laminate contain 50% MMC in the outside layers and 50% Vol. IMI834 in the middle of the laminate. The C-type laminate contains the same volume fraction of IMI834 and MMC, but here the MMC is in the middle of the laminate. Bonding parameters: temperature, pressure and time have been optimised. Effective Young's Modulus and bend strength have been investigated using four-point bend tests, and impact fracture toughness of the laminates and control samples have been assessed by using an instrumented impact testing. For un-notched specimens, 100% IMI834 has highest fracture toughness with lowest E and strength; MMC, in contrast, has higher strength and lowest fracture toughness. However, for notched specimens, both of them have lower strength and fracture toughness compared with the S-type laminate. The measured stiffness (E) for the S-type laminate was greater than that for IMI834 by about 1.7. By laminating materials, the impact fracture toughness of S-type laminate for un-notched and notched specimens, compared with 100% MMC material, increased by about 2.7 and 4.6. Young's modulus strength, and fracture toughness can be optimised by selecting different structures. Lamination by combining tough matrices and reinforced components is an effective way to improve toughness for high strength materials, like MMC, and the properties of the materials can be tailored according to a particular application.
PROCESSING OF Ti/SiC COMPOSITES: A COMPARATIVE STUDY OF THE FOIL-FIBRE-FOIL AND THE TAPE-CASTING TECHNIQUES: Zheng Xiao GUO, Department of Materials, Queen Mary and Westfield College, University of London, Mile End Road, London E1 4NS, UK
Ti-based SiC fibre reinforced composites are strong, stiff and light-weight materials for high temperature applications up to 700-1000°C. As with any other advanced materials, their development has to overcome both economic and technical hurdles. Here, a study into the foil-fibre-foil and the tape-casting processing techniques is reported. The fundamental procedures involved in the techniques are compared and discussed. Possibilities of reducing product costs are analysed. Due to the reactive nature of titanium, the composites must be processed under minimum thermal exposure to reduce undesirable fibre/matrix interfacial reactions: on the other hand, care should also be taken not to use too low a temperature or too large a pressure in order to avoid fibre breakage. This requires an optimum balance of the processing temperature, pressure and time. Therefore, both theoretical and experimental investigations were conducted for the consolidation of aligned fibre mats with matrix foils or with matrix powder-tapes. The effects of processing parameters, such as temperature pressure and time, on the mechanisms of identification are evaluated. Predictions of the process model are compared with experimental findings, which shows satisfactory agreement. Various types of interfacial defects and fibre breaking have been analysed in relation to the processing parameters and fibre/matrix lay-ups. Consequently, defect- and reaction- free composites have been obtained. This is particularly successful with the assistance of a temporary hydrogenation procedure using either pre-hydrogenated foils or powder particles during processing.
10:00 am BREAK
CHARACTERISATION OF SIGMA SIC FIBRE/TITANIUM ALLOY MMCS FABRICATION BY PLASMA SPRAYING AND FOIL/FIBRE METHODS: A.M. Baker, P.S. Grant, M.L. Jenkins , C.M. Ward-Close, Z. Fan, B Cantor ,OCAMAC, Department Of Materials University of Oxford, Parks Road, Oxford OX1 3PH, UK
A new process for vacuum plasma spray manufacturing of multi-ply Titanium/SiC fibre MMC rings has been developed. Material produced can be identified easily by subsequent vacuum hot pressing or HIP. Ti and Ti-6A1-4V matrices have been 'spray-wound' with C coated and C/TIBx coated DRA Sigma SiC fibres. Characterisation by electron microscopy has identified interfacial reaction products, showing that the fibre/matrix reaction is similar to that for plasma sprayed monotapes. SiC fibres chemically extracted from the matrix have been subjected to tensile and bend testing to quantify process damage for spray-wound and foil/fibre material. This has shown that fibre damage from spray/winding is of a similar magnitude to that from foil/fibre processing. Possible mechanisms for fibre damage during processing have been identified.
CONSOLIDATION OF CONTINUOUS SiC/Ti-6Al-4V MATRIX-COATED FIBRE METAL MATRIX COMPOSITES: S. Schuler, B. Derby, M.J. Wood, C.M. Ward-Close1, Oxford Centre for Advanced Materials and Composites, OCAMAC, Department of Materials, University of Oxford, Parks Road, Oxford , OX1 3P; Structural Materials Centre, Defence Research Agency, DRA, Farnborough Hampshire, GU14 6TD, UK
The consolidation of continuous matrix-coated fibre Metal Matrix Composites, MMC, has been investigated using a theoretical as well as an experimental approach. A numerical, quantitative model has been developed for the solid-state consolidation of continuous Matrix-Coated Fibre, MCF, Metal Matrix Composites. In addition, an experimental verification programme was conducted using two different samples types, one produced under normal conditions and one containing yttrium maker layers. The marker layers were used to make the matrix deformation visible, which occurs during the consolidation, and hence offered the opportunity of a direct comparison of the predicted matrix deformation and the experimentally determined matrix deformation. The materials investigated were continuous Textron SCS-6 SiC fibres in a Ti-6A1-4V metal matrix. The fabrication route chosen was the Matrix-Coated Fibre method, developed by the DRA Farnborough, UK. In this method, the fibres are pre-coated prior to consolidation with the matrix material using Electron Beam Evaporation, a Physical Vapour Deposition technique. The thickness of the matrix-coating and hence the final fibre volume fraction of the composite can easily be varied by adjusting the coating time. For the consolidation to the final composite the matrix-coated fibres are stacked, degassed placed into a titanium container and hot-isostatically pressed. The analytical model is based on a Finite Element Model, FEM.
RECENT ADVANCES IN FIBER COATING TECHNOLOGY FOR USE IN SiC/Ti-MMCs: D. Upadhyays, P. Tsakiropoulos, and F.H. Froes, Institute for Materials and Advanced Processes, University of Idaho, Moscow, ID 83844-30261; Department of Materials Science and Engineering, University of Surrey, Guildford, Surrey, GU2 5XH, UK: Structural Materials Centre, DRA Farnborough, Hants GU14 6TD, UK
Continuous silicon carbide fibre-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 fibre to combat interfacial chemical reactions as well as to accommodate large mismatch in the coefficient of thermal expansion (CTE) between the SiC fibre and titanium matrix. This paper describes the strategy for designing coating for continuous silicon carbide fibre 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 -TiA1. The newly developed coating system, designated FUWT1. 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 a reaction barrier (protect the SiC fibre from reactions with titanium up to 100°C) and a compliant layer (absence of thermal cracking in AiA1 based composite). The interfacial shear strength of an as-fabricated SiC/FUWT/Ti-6A1-4V was found to be higher than the presently available SCS6/Ti-6A1-4V and Sigma (SM1240)/Ti06A1-4V composites. From the surnames of the four co-inventors: Froes, Upadhyaya, Ward-Close and Tsakiropoulos.
THE MANUFACTURE OF Ti ALLOY/SiC FIBRE COMPOSITES BY A NEW SPRAY/WIND PROCESS: Z.Y. Fan, P.S. Grant, B. Cantor, Department of Materials, Oxford University, Parks Road, Oxford OX1 3PH, UK.
This paper describes a new method of manufacturing Ti alloy/SiC fibre reinforced composites. Three dimensional hoop reinforced rings, cylinders and tubes are being manufactured by concurrent plasma spraying of titanium alloy and mechanical winding of SiC or other reinforcing fibres or wires. The paper will outline the manufacturing process concentrating on the range of geometry's which can be manufactured, and will discuss the variety of microstructures which can be achieved.
SYNTHESIS AND PHASE EQUILIBRA IN TiB2 PARTICLE REINFORCED HIGH MODULUS STEEL: Kouji Tanaka, Tadashi Oshima, and Takashi Takashi Saito, Toyota Central R&D Labs, Inc., 41-1 Yokomichi, Nagakute, Aichi, 480-11, JAPAN
This paper describes the synthesis of high modulus steel for automobile parts with an emphasis on its alloy-designing concept and phase equilibrium. Titanium diboride (TiB2) particles have been verified to be the best reinforcement for improving isotropic Young's modulus of steels. The calculated phase diagram shows that TiB2 has a narrow tow-phase equilibrium window with carbon-free Fe-Cr-Ti ferric steel and has neither solubility of iron nor chromium. Those thermo-dynamical stability's of TiB2 are responsible for maintaining its own high Young's modulus of 540GPa in the ferocity steel. Both pre-mixed and in-situ TiB2 particles effectively reinforced the ferocity steel matrix. The developed steel with 30vol.%TiB2 showed a Young's modulus of 280GPa which apparently corresponded to 350GPa due to its reduced density of 6.6g/cc compared with 7.8g/cc of the conventional steel.
LIGHT WEIGHT CELLULAR STRUCTURES BASED ON ALUMINIUM COMPOSITES: O. Prakash, Dept. of Mechanical Engineering, Indian Inst. of Technology, Kanpur 208016, India; J.D. Embury, C. Sinclair, Dept of Materials Science and Engineering, McMaster University, Hamilton, Ontario, L8S 4L7, Canada; H. Sang, Metallurgy Dept., Queenís University, Kingston, Canada; P. Silvetti, F.A.M.A.F. Dept. of Physics, University of Cordoba, Argentina
An interesting form of light weight material which has emerged in the past two decades is metallic foam. This paper deals with the basic concepts of making metallic foams and a detailed study of foams produced from Al-SiC. In addition some aspects of cellular solids based on honeycomb structures are outlines including the concept of producing both two phase foams and foams with composite walls.
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