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Session Chairpersons: P. Grant, University of Oxford, Department of Materials, Parks Road, Oxford OX1 3PH, UK; M.A. Iman, US Navy Naval Research Lab, Materials Science & Technology Div., Washington, DC 20375
FABRICATION OF TiNi INTERMETALLIC COMPOUNDS BY SELFPROPAGATION HIGH-TEMPERATURE SYNTHESIS PROCESS (SHS): Suk-Kwon Ko, Joong-Chai Jung, Jong-Hyeon Lee, Chang-Whan Won, Rapidly Solidified Materials Research Center(RASOM), Chungnam National University, Yuseong, Taejon, 305-764 Korea
TiNi intermetallic compounds were manufactured by the self-propagating high-temperature synthesis process. The effects of chemical composition(Ni/Ti=0.5 ~2.0 molar ratio), compaction pressure and preheating temperature on the reaction were investigated. As the molar ratio of Ni, compacting pressure and preheating temperature were increased, the combustion temperature and its velocity were increased. In the every mole ratio of M, without preheating, secondary phases such as Ti2Ni, TiNi3, Ti3Ni4 as TiNi were found in the products according to the XRD analysis. At the same condition, the products prepared by of 200 were TiNi single phases by perfect reaction. Hence, the reasons to form the different phases during the reaction and the forming mechanism of TiNi for combustion reaction were discussed.
RAPID SYNTHESIS OF NANOSTRUCTURAL INTERMETALLICS AND THEIR BULK MECHANICAL PROPERTIES: S.M. Pickard, A.K. Ghosh, Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109-2136
A PVD process has been developed to produce bulk intermetallics at high rate by direct vacuum evaporation. Independent elemental sources are directly heated using 5kW electron beams and the evaporate is deposited as a nanolaminated (layered) structure at a rate of 1-mm/minute on a rotating substrate. Insitu reaction occurs on the heated substrate to produce a homogenous nanograined bulk intermetallic deposit. The deposit can be further thermomechanically processed to produce optimum mechanical properties. TIA1, NiA1 binary and ternary alloy systems has been chosen for initial evaluation of potential mechanical property and processing advantages of bulk PVD. Both relatively thin 9140-180mm) and relatively thick (2.3) mm) layers of intermetallic alloys, have been formed. Hardness characterisation of the -deposited film shows a Vickers hardness value which is 2-3 times higher than the expected value for an as cast alloy. An initial flow stress of 700-800 MPa has been observed for the T1A1, which is higher than that of conventional cast material, with delimitation failure of the layered material. Tests on the bulk material using 3-Point banding indicate and rupture strength of 450-500MPa for Ti-30a% A1, with linear-elastic loading response to failure, indicative of extrinsic defect controlled strength. Elevated temperature tensile tests are being conducted on the intermetallics to determine rate sensitivity.
DEVELOPMENT OF Nb3Al Mo and Nb3Al TiCr BASED ALLOYS: E. Passa, G. Shao, P. Tsakiropoulos, Dept. of Materials Science and Engineering, University of Surrey, GU2 5XH, UK
Abstract not available.
COMPRESSIVE STRENGTH AND FATIGUE PROPERTIES OF BE-A1 ALOYS: R. Schneeberger, B. Bavarian, School of Engineering and Computer Science, California State University at Northridge, Northridge, CA 91330; R. Hayes, Metals Technology, Inc. 19080 Nordhoff St, Northridge, CA 91330
Both 40 and 62 wt% beryllium compositions were evaluated for ambient and elevated temperature compressive strength at low and high strain rates. Data indicated a strong influence of beryllium percentage along with an increase of yield point for fast strain rates of 0.5-3 in/in/minute. Fatigue properties of a ternary Be-A1-Ag cast and extruded material were determined for full reversal and standard tension fatigue conditions. Typical S-N curve behaviour including endurance limit was observed.
CREEP BEHAVIOUR OF TWO BERYLLIUM-ALUMINIUM ALLOYS: R. Schneeberger, B. Bavarian, School of Engineering and Computer Science, California State University, Northridge, 18111 Nordhoff St, Northbridge, CA 91330; R. Hayes, Metals Technology, Inc 19080 Nordhoff St, Northridge, CA 91330.
Creep testing performed on 40 and 62 wt% beryllium compositions of a power metallurgy composite alloy at several elevated temperatures indicated a dependence of steady state creep rates and times to rupture on beryllium content, test direction, stress, and test temperature. A stress exponent of 8.5 for 40% beryllium and 10 for 62% beryllium was obtained form tests at 550 degrees F 630 degrees F. Activation energies for creep were somewhat higher than for self-diffusion in either pure metal, and exhibited significant anisotropy.
3:40 pm BREAK
BERYLLIUM ALUMINUM ALLOY DEVELOPMENT FOR INVESTMENT CASTING: Nancy F. Levoy, Brian J. Smith, Nuclear Metals Inc., 2229 Main St., Concord, MA 01742
Be-Al alloys are unique, light weight, composite alloys that combine high specific stiffness and substantial strength with good ductility and toughness. This combination of properties makes these alloys attractive for many high performance aerospace applications. Due to the inherent problems associated with casting Be-Al alloys, processing of these alloys has previously been restricted to rolling or extrusion of prealloyed powder compacts. Beralcast(363 is a new cast in-situ composite alloy containing 65 wt% Be that is formed by the controlled solidification processing of a higher-order Be-Al alloy. This paper will describe the development of the Beralcast( family of alloys specifically for production of near net shape components via investment casting.
OXIDATION BEHAVIOUR OF Nb3A1-xMo ALLOYS: E. Passa, G. Shao, P. Tsakiropoulos, Department of Materials Science and Engineering, University of Surrey, Guildford, Surrey GU2 5XH, England, UK
Phase selection and microstructural refinement in Nb-17A1-xMo (x=20,30,40) alloys can be controlled via alloy design and solidification processing route. The formation of ordered (B2) or disordered (A2) phases in the as cast microstructures of cold hearth processed ingots and cold hearth melt overflow processed ribbons will be briefly reviewed. DSC and TG studies of the ingots and ribbons will be discussed with emphasis on the oxidation behaviour of the alloys. It will be shown that additions of Mo can improve the oxidation behaviour of Nb3A1.
GRAIN SIZE CONTROL AND PROPERTIES OF TiAl-BASED ALLOYS: S. Davey, P. Gouma, A. Godfrey, D. Hu, P.A. Blenkinsop, M.H. Loretto, IRC in Material for High Performance Applications, The University of Birmingham, Edgbaston B15 2TT, UK
The production of TiA1-based alloys with small grain sizes has been approached in two distinct ways. Firstly, by addition of B-containing compounds to the melt and secondly via atomisation and subsequent processing. These route coupled with hot extrusion, allow control of the microstructure of these alloys so that a wide range of properties can be obtained. Results for several different alloys will be presented and the influence of composition on control of microstructure and hence of properties will be illustrated.
MICROSTRUCTURE AND MECHANICAL PROPERTIES OF GAMMA TITANIUM ALUMINIDE STRIP: Gopal Das, Pratt & Whitney, P.O. Box 109600, West Palm Beach, FL-33410-9600
Thin gamma titanium aluminide (Ti-45A1-2Cr-2Nb at.%) series, 20 mils thick, were produced by the melt overflow rapid solidification technology (MORST) process. The microstructure resulting from heat treatments was studied by a combination of optical, X-ray, SEM and TEM methods. Transition temperatures including the alpha transits temperature were determined by DTA. Textures of gamma TiA1 strips were studied on as-cast and heat treated specimens. The microhardness was measured for specimens subjected to different heat treatments. Tensile properties of heat treated specimens were determined at RT-760°C along the strip growth direction and perpendicular to it. The material failed in a brittle manner at RT for both orientations. It started to yield at 650°C and at 760°C, it failed in a ductile manner. The strain-to-failure along the direction perpendicular to strip growth direction was poor. Deformation microstructure was analysed by TEM and fractographs were studied. Results will be compared with those of investment cast and wrought gamma titanium aluminised. This work was supported by NASA LeRC, Cleveland, OH under Contract No. NAS3-26385.
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