Materials Week '97: Monday PM Session

Focusing on physical metallurgy and materials, Materials Week '97, which incorporates the TMS Fall Meeting, features a wide array of technical symposia sponsored by The Minerals, Metals & Materials Society (TMS) and ASM International. The meeting will be held September 14-18 in Indianapolis, Indiana. The following session will be held Monday afternoon, September 15.

PROCESSING TECHNOLOGIES: General Abstract Session

Session Chair: Eric Rodeghiero, Cornell University, Ithaca, NY 14853

INVESTIGATION OF PROCESSING PARAMETERS FOR LASER DIELESS SUPERPLASTIC FORMING: N. Hu, C.W. Chen, T.R. Bieler, R. Averill, K. Mukherjee, High Energy Processing Laboratory, Dept. of Materials Science and Mech., Michigan State University, East Lansing, MI 48824

The feasibility of the Laser Dieless Superplastic Forming has been demonstrated. This novel laser processing technique employs a CO₂ laser generator and a numerically controlled x-y moving table, for superplastic forming of an aluminum alloy sheet mounted on the top of a vacuum chamber. Some processing parameters such as the laser power, laser spot diameter, scanning speed and cooling conditions have been investigated. These parameters have critical influence on the temperature distribution of the deformed area, the total strain and the strain rate. An evaluation of the microstructure and the thickness variance in cross section of the specimen and an analysis of the stress distribution and heat flow appropriate to the process will be presented.

2:20 pm

MATHEMATICAL MODELING OF LASER BEAM MACHINING AND DUAL LASER BEAM WELDING OF METAL MATRIX COMPOSITE: S. Kudapa, V. Barnekov, K. Mukherjee, Department of Materials Science and Mechanics, Michigan State University, East Lansing, MI 48824

A simplified analytical model of laser beam machining will be presented to determine the maximum depth of cut for a given traverse speed and laser power. The correlation between the analytical and experimental results will be discussed. Variation in the absorptivity of the material to the laser beam was also accounted in the mathematical model. The collinear dual laser beam welding (CD-LBW) technique pioneered by High Energy Laser Material Processing Laboratory at MSU, was also modeled using a commercial FEM package and the results were compared with the experimental values.

2:40 pm

SYNTHESIS AND CHARACTERIZATION OF RAPIDLY SOLDIFIED POWDERS OF A HYPOEUTECTIC CAST IRON: S.N. Ojha, Dept. of Metallurgical Engineering, Banaras Hindu University, Varanasi-221005, INDIA; Presently at Dept. of Chemical Engineering, SH470, Cleveland State University, Cleveland, OH 44115

A confined gas atomization process is described to synthesize rapidly solidified powders of a hypoeutectic cast iron melt. The process basically utilizes the melt-gas interaction at the tip of a flow tube concentric to an annular gas flow channel to promote an efficient atomization of the melt. The effect of gas-metal flow ratio on the size and size distribution of powder particles are discussed. The results of X-ray diffraction analysis are used to show a large volume fraction of retained austenite in different size range of powder particles indicating considerable departure from their equilibrium solidification conditions. The microstructural features are presented to show a typical cellular and dendritic morphology of the primary austenite phase depending on the size of powder particles. The cooling rates estimated from the microstructral features and also from the heat flow model are presented and compared to show that these are well within rapid solidification regime for a wide size range of powder particles.

3:00 pm BREAK

3:10 pm

CONTROL OF SILICON CARBIDE/METAL REACTIONS: J.S. Park, K. Landry, J.H. Perepezko, Dept. of Materials Science and Engineering, University of Wisconsin-Madison, 1509 University Ave., Madison, WI 53706

The diffusion pathway and kinetics governing the reaction between SiC/metal combinations have been examined to identify systematic behavior. With respect to the metal components, two separate reaction modes were identified formation of carbides and development of silicides or formation of silicides and free carbon (periodic morphology). In each case, the diffusion pathway is dictated by the formation of carbon or carbides, and mass balance requirements. The analysis of the separate reaction modes was confirmed by experiments of SiC/Ni, SiC/Cu/Ni and SiC/Cr/Ni reactions. For the SiC/Ni reaction at 1123K, the chemical potential of Ni and Si decreased but that of carbon increased and decreased along the reaction path with formation of silicides and free carbon. The analysis method offers general guideline for the control of in-situ composite synthesis reactions The support of ONR (N0001492-J-1554) is gratefully acknowledged.

3:30 pm

IMPROVEMENT OF CYCLIC OXIDATION RESISTANCE OF CARBON-CARBON COMPOSITES BY Si IMPREGNATION: Y. Sato, S. Ohtani, Y.-C. Zhu, N. Iwamoto, Ion Engineering Research Ins. Corp., 2-8-1 Tuda-Yamate, Hirakata, Osaka, 573-01 Japan

To improve high temperature oxidation resistance of carbon-carbon composites following surface treatment was performed before CVD SiC coating. The surface of C/C composites were exposed by SiO gas for forming thin SiC layer. Then Si impregnation at high temperature was performed. The pores existing at the surface region of C/C composites were almost infiltrated with SiC. SIG-C composite zone and furthermore smooth surface were formed.

The surface modified C/C composites were SiC coated by using conventional CVD method and then cyclic oxidation tests at 1500°C in air or in methane-combusted atmosphere were performed. SiC coated C/C composites after Si impregnation showed improved oxidation resistance although C/C composites directly covered with CVD SiC showed a greater mass loss.

3:50 pm

NONDESTRUCTIVE EVALUATION OF MECHANICAL AND ENVIRONMENTAL DAMAGE IN A CONTINOUS SWIRL GLASS REINFORCED POLYURETHANE COMPOSITE: H.M. Herring, D.C. Worley II, R.S. Benson, P.K. Liaw, Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996; J.M. Corum, W.A. Simpson, Jr., Oak Ridge National Laboratory, Oak Ridge, TN 37831

This paper describes research into the methods by which a glass reinforced polymer composite may be examined nondestructively for fatigue and creep damage. Glass fiber reinforced polyurethane composite samples were mechanically tested in standard conditions and after exposure to two distinct environments, and studied using various nondestructive test methods. Specifically, continuous swirl glass mat (CSM) polyurethane samples were fatigue and creep tested in a standard environment and after being subjected to distilled water and windshield washer fluid. Virgin specimens were examined prior to testing, using C-scan ultrasonics and light-transmission microscopy (LTM). After mechanical testing, the samples were again examined with C-scan ultrasonics and LTM to document the damage sustained. Additionally, any specimens that failed during the fatigue or creep tests were further examined by scanning electron microscopy (SEM) to evaluate damage on any existing fracture surfaces. Subsequent analysis of the C-scans and LTN images displayed a general tendency toward increased attenuation in the post-teat samples, believed to be the result of sustained damage. In the C-scans, changes in the increase in attenuation of ultrasonic waves appeared to be more attributable to the different environments. Increased attenuation of transmitted light in the LTM images, however seems to be due more to mechanical damage, such as fiber/matrix interfacial debonding. Selected C-scans, LTM, and SEM images are presented, and a comparison is made of the images taken prior to mechanical testing and those taken afterwards. Some advantages and disadvantages of using these techniques to determine damage in this composite are discussed.