Wednesday, PM Room: B4
February 7, 1996 Location: Anaheim Convention Center
Session Chairperson: TBA
FACTORS LEADING TO THE MICROSTRUCTURAL REFINEMENT AND ELIMINATION OF MICROPOROSITY IN DROPLET-BASED FREEFORM FABRICATION OF STRUCTURAL MATERIALS: M. Orme, J. Courter, C. Huang, Department of Mechanical and Aerospace Engineering,University of California, Irvine, CA 92717-3975
The development of a droplet-based freeform fabrication technique for the fast manufacture of metallic structural components directly from CAD information is presented. The technique relies on the use of precisely controlled molten nano-liter droplets as the deposition element. Encouraging experimental results indicate that typical material porosities as low as 0.03% and microstructures with grain sizes on the order of a micron can be achieved with molten droplet throughput rates as high as .18 ml/s with a single droplet stream. Extremely high control of the droplet trajectories (measured angular dispersions of the order of 1 micro-radian), and droplet speeds (measured speed dispersions of the order of 3x10-7times the average stream speed) provides the ability for precise control over the solidification characteristics and hence microstructure. Experimental results from parametric studies combined with results from numerical analyses on the solidification characteristics of the droplets determine a control scheme for achieving a controlled droplet deposited part with minimum porosity and microstructure.
FABRICATION OF Ti-Al INTERMETALLIC SHEETS VIA HOT ROLLING OF Ti AND Al MULTILAYER FOILS: W. J. Park, W. C. Lee, S. Lee, Nack J. Kim, Center for Advanced Aerospace Materials, Pohang University of Science and Technology, San 31, Hyojadong, Pohang 790-784, Korea
Ti-Al based intermetallics possess high specific strength and specific modulus, and high resistance to oxidation, which make them attractive for a variety of applications. However, these intermetallics are difficult to fabricate into near net shape using conventional processing due to their lack of ductility. It has recently been shown that a self-propagating, high temperature synthesis (SHS) can be used to produce near net shape intermetallic parts based on Ti and Al. Such processes usually involves the press and sinter or powder forging of elemental powders or the hot pressing of elemental foils. The present study is aimed at fabricating the Ti-Al intermetallic sheets via hot rolling of Ti and Al foils. It has been shown that the microstructure of hot rolled sheets consists of three phases; TiAl, Ti3Al and Al3Ti. Subsequent heat treatment of hot-rolled sheets results in the changes in the relative amounts of these three phases. The microstructural development will be discussed as functions of hot rolling and heat treatment conditions.
PREPARATION OF SiC POWDER BY SELF-PROPAGATING HIGH TEMPERATURE SYNTHESIS PROCESS FROM SILICA: Chang Whan Won, Seong Seock Cho, Byong Sun Chun, Engineering Research Center for Rapidly Solidified Materials Chungnam National University, Taejon 305-764
The SiC powder was prepared by a SHS processing using SiO2, Mg and C as raw materials to determine the optimum process variables. The results obtained from this study may be summarized as follows; 1) The mole ratio between C and Mg affected the magnesiothermic reduction reaction most and the highest yield of SiC was obtained at the mole ratio of SiO2: Mg: C = 1.0: 2.5: 2.2. 2) The propagation speed of combustion reaction was about 10mm/sec increasing with the decrease of SiO2 particle size. 3) The amount of unreacted silicon decreased with increasing compaction pressure. 4) Impurities were found to decrease by evaporation during the high temperature reaction or by solution during leaching process. 5) The particle size of prepared SiC powders was in the range of 0.2 ~ 1.0 microns with the purity of about 98.885 weight percent.
ALTERNATIVE PROCESSING METHODS FOR TUNGSTEN-BASE COMPOSITE MATERIALS: E. K. Ohriner, V. K. Sikka, Metals and Ceramics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6083
Tungsten composite materials contain large amounts of tungsten distributed in a continuous matrix phase. Current commercial materials include the tungsten-nickel- iron and related materials and also tungsten-copper materials. In the past few years, there has been interest in a wider range of matrix materials, which offer the potential for superior properties. These must be processed by solid-state processes and at sufficiently low temperatures to avoid undesired reactions between the tungsten and the matrix phase. These processes, in order of decreasing process tempeMture requirements, include hot-isostatic pressing, hot extrusion, and explosive compaction. The results of laboratory-scale investigations of solid-state consolidation of a variety of matrix materials including titanium, hafnium, copper, nickel aluminide, and steels are reviewed, including the limited available mechanical property data. The potential advantages and disadvantages of each of the possible alternative consolidation processes are identified. Managed by Lockheed Martin Energy Systems under contract DE-AC05- 840R21400 with the U.S. Department of Energy.
3:20 pm BREAK
SINTERING OF CUBIC BORON NITRIDE PARTICLES COATED WITH ULTR-FINE TITANIUM-METAL PARTICLES: H. Yoshida, National Institute for Advanced Interdisciplinary Research (NAIR), 1-1-4 Higashi, Tsukuba, Ibaraki 305, Japan; S. Kume, National Research Institute of Nagoya (NIRIN), Japan; Y. Yamada, T. Fuyuki, Nisshin Flour Milling Co., Ltd. Technical Research Center, Japan; Y. Sumita, K. Kimura, Read Co., Ltd., Japan
Pine-grained cBN whose grain-size is 0/2m was successfully coated with ultra-fine titanium-metal particles whose grain-size is less than 0.1m by PVD without creation of hBN. Tablets of the coated cBN were processed by a cubic-type high pressure apparatus under 5.5GPa at 1723K for 30 min. That is not too severe ultra-high pressure sintering condition but typical condition for industrial production of cBN sinter bodies. Reaction of cBN and titanium-metal during sintering resulted in dense cBN sintered body whose microstructure consists of more-fine-grained cBN than raw materials, and of binding material of TiN-TiB2. Hardness of the sintered body containing 83vol%cBN was fairly higher than that of the cBN-cutting tools on the market.
A MONTE CARLO SIMULATION OF POWDER COATING USING TUMBLING FLUIDIZED BED: Hiroyuki Nakamura,Eiichi Abe, Noriyuki Yamada, Kyushu National Industrial Research Institute, Shuku-machi, Tosu, Saga, 841 Japan
In a preparation of coated particles, homogeneous distribution of coating mass is often desired and a lot of effort is made to accomplish it. If it is possible to reproduce the effect of operating conditions on coating mass distributions by computer simulations, the effort will be reduced. From this point of view, in this study, Monte Carlo simulations for coating mass distribution of particles were performed to reproduce the results obtained by using tumbling fluidized bed. As the result, this method was found to be applicable to reproducing the experimental tendency of the effect of operating conditions on the coating mass distribution, showing more homogeneous coating mass distribution was achieved under these conditions; long coating time, small hold up of core particles, large mixing rate of particles etc. Furthermore, some predictions of the effect of operating conditions on coating mass distributions using this simulation method were performed.
COATING MASS DISTRIBUTIONS OF THE CORE PARTICLES IN A TUMBING FLUIDIZED BED COATER: Eiichi Abe, Noriyuki Yamada, Hideharu Hirosue and Hiroyuki Nakamura, Kyushu National Industrial Research Institute, Shuku-machi, Tosu, Saga 841 Japan
In order to control the extent of the function of coated particles, it is necessary to clarify how each individual core particle is coated quantitatively. In this work, coating mass distribution of core particles in a tumbling fluidized bed coater, having a rotary disk at the bottom of the coating chamber, was investigated experimentally. As the results, coating mass per unit surface area of core particles was found to obey a normal distribution by number. Coefficient of the variation of coating mass distribution, cv, varied depending upon the operating variables of the coater. It was found that cv decreased with increasing coating time and size of core particle and with decreasing holdup of core particles and concentration of the coating substance in a spraying solution. However, rotational speed of the disk, effective to force aggregative coated particles apart, hardly affected cv.
TI(ON)-WO-TaC-Ni-Co CERMETS; PROCESSING & MICROSTRUCTURE: S. Kang, Seoul National University, Seoul, Korea (02) 880-7167
Some issues in the dissociation behavior of a carbonitride solid solution, the transport and precipitation phenomena of second phases in the binder phase were investigated with a TI(ON)-WO-TaC-Ni-Co system. It was shown experimentally that the dissociation of the cubic phase occurred at a fixed ratio of carbon to nitrogen. This indicated that the nitrogen in the cubic phase has a stronger affinity with the metallic species that expected, making the system of interest relatively stable at higher temperatures. For the reactions occurring in the binder phase, the effects of sintering conditions on the binder structure were measured with coercive force (Ho) and magnetic saturation (a). This study showed some evidence that the precipitation in the heating stage influence the binder microstructure extensively and nitrogen can transport to the surface in the form of voids during sintering. The issues were discussed with the results of an analytical electron microscopy and thermodynamic principles.
FOAMING PROPERTIES OF ALUMINA HYDRATE-COATED FINE VOLCANIC GLASS: Kunio Kimura, Hiroyuki Nakamura, Kyushu National Industrial Research Institute, Calceed Co., Ltd., Shuku-machi, Tosu, Saga 841 Japan; Hiromi Okada, 4611-1 Isa, Isa-machi, Mine, Yamaguchi 759-22 Japan
The hollow glass microspheres larger than a few decades microns have been produced from natural volcanic glass particles (VGP) by heat treatment. However, it was difficult to produce hollow glass microspheres less than 10 microns resulting from the insufficient amount of water in VGP for foaming. Homogeneous precipitation technique was applied to coating VGP with alumina hydrate to inhibit the release of water vapor from the particle surface under heating. VGP ranging from 5 to 10 microns were suspended in the aqueous solution of aluminum sulfate and urea. Alumina hydrate-coated VGP were obtained by heating the suspension at 80deg.C for 4 hours. Fine hollow glass microspheres of around 10 microns could be produced from alumina hydrate coated VGP by heat treatment of 1040°C for a few seconds.
ADVANCED CERAMIC: Rajeev Agrawal, Rajendra Kumar Goya, Department of Metallurgical Engineering Malaviya Regional Engineering College, Jaipur, India
Advanced Ceramics are a relatively new class of high performance material with a significant potential for future economic impact. This paper deals with processing and applications of sialons. By substituting some of the silicon and nitrogen in silicon nitride by aluminium and oxygen the sialon ceramics are formed. During sintering, silica (SiO2) on the surface of the silicon nitride particle reacts with alumina and yttria, to form a low melting liquid. The silicon nitride reacts with this liquid to form sialon. Sialons have been shown to work efficiently both at low and high speeds. Sialon has been successful in machining super alloys at considerably high speeds.
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