Program Organizers: Narendra B. Dahotre, Center for Laser Applications, University of Tennessee Space Institute, Tullahoma, TN 37388; Janet M. Hampikian, School of Materials Science & Engineering, Georgia Institute of Technology, Atlanta, GA 30332; Jacob J. Stiglich, PO Box 206, Sierra Madre, CA 91025
Monday, AM Room: B1
February 5, 1996 Location: Anaheim Convention Center
Session Chairpersons: Sun K. Kim, Department of Metallurgical Engineering, University of Ulsan, Kyung Nam, Korea 680-749; Narendra B. Dahotre, Center for Laser Applications, University of Tennessee Space Institute, Tullahoma TN 37388
8:30 am OPENING REMARKS
Narendra B. Dahotre, Center for Laser Applications, University of Tennessee Space Institute, Tullahoma TN 37388
8:40 am Invited
FORMATION OF WEAR-RESISTANT VANADIUM CARBIDE AND NITRIDE LAYERS ON TOOL STEEIS: Sun K. Kim, Department of Metallurgical Engineering, University of Ulsan, Kyung Nam, Korea 680-749
When steels are heated at 900 - 1000[[ring]]C in a fused borax bath containing Fe-V powder, vanadium carbide layers are formed on the steel surfaces. Effect of steel composition and the treating condition on the growth rate of the vanadium carbide layers were investigated. Hardness and wear resistance of such layers were determined. Also nitriding and vanadium carbide forming was combined to obtain better properties of treated specimen. EPMA analysis was done for this V(C,N) type layer. Hardness and wear resistant properties of such treated specimen were investigated.
DEVELOPMENT OF A CONVERSION COATING FOR SILICON CARBIDE: S.C. Kung, Babcock & Wilcox, Alliance Research Center, 1562 Beeson Street, Alliance, OH 44601
The formation of a chromium-carbide conversion coating on SiC has been demonstrated using the pack cementation technique. The conversion coating would improve the high-temperature corrosion resistance of SiC and its derivatives, such as SiC-based composites and continuous fibers, by forming a protective Cr2O3 scale upon exposure to corrosive environments. The coating consists of a multi-layered structure with each of the sub-layers containing a high Cr concentration. In addition, the conversion coating is relatively dense compared to the underlying porous SiC substrate material. Such a coating morphology is highly desirable for many applications when impermeability is required.
PLASMA SPRAYED MoSi2/SiC COATINGS: J. Wolfenstine, X Liang, E.J. Lavernia, Department of Chemical and Biochemical Engineering, University of California, Irvine, CA 92717-2575; A. Sickinger, Sulzer Metco (Irvine) Inc., 17426 Daimler Street, Irvine, CA 92714
Various processing techniques for the synthesis of MoSi2 composite coatings reinforced with SiC particles using low pressure plasma spraying will be presented. The microstructure and thermal behavior of the coatings were characterized using x-ray diffraction, scanning and transmission electron microscopy, x-ray photoelectron spectroscopy and dilatometry. In addition, the room temperature fracture toughness and high temperature creep behavior were investigated and compared to MoSi2-SiC particulate composites prepared by powder metallurgy methods.
A STUDY ON THE MICTROSTRUCTURAL DEVELOPMENT OF PLASMA SPRAYED CERAMIC COATINGS: Seiji Kuroda, Takeshi Fukushima and Shigiru Kitahara, National Research Institute for Metals, Advanced Materials Processing Division, 1-2-1, Sengen, Tsukuba-shi, Ibaraki, 305 Japan
Plasma sprayed ceramic coatings are widely in use for high temperature applications such as thermal barrier coatings in jet engines and power generators. However, the relationship between a number of process parameters and the microstructure of these coatings is not well established. Sprayed coatings consist of layers of rapidly solidified splats. The paper deals with the most important microstructural features of ceramic coatings, i.e., microcracks within splats and interlamellar gaps. A theoretical model to correlate the spray conditions and the density of microcracks is presented first. Then, experimental evidences on the pore structure within coatings are compared with the theory. Importance of the substrate temperature during spraying on the interlamellar bonding is also demonstrated.
CHEMICAL PROPERTIES OF SODIUM BERATE COATINGS: R.G. Reddy, J.Y. Yen, Department of Chemical and Metallurgical Engineering, University of Nevada, Reno, NV 89557
A thermodynamic study of ionic species distribution of high temperature sodium borate glass coating melts was undertaken to understand the boron anomoly. Mole fraction of BO3, B306, and B409 structural units in the depolymerized portion of borate melts were calculated at 1123K and as a function od composition. The addition of Na2O cause the boroxol ring breakdown into basic triangular structure unit BO3.
EVOLUTION OF MICROSTRUCTURE DURING LASER INDUCED REACTION COATING OF ALUMINA ON SiC/Al2O3 COMPOSITE: Narendra B. Dahotre, C. Xiao, W. Boss, M.H. McCay, T.D. McCay, Center for Laser Applications, University of Tennessee Space Institute, Tullahoma, TN 37388
The protection of SiC/Al2O3 composite at high temperature from deleterious reactions occurring within and with the surrounding environment is required for several high temperature applications. The development of continuous Al2O3 coating on SiC/Al2O3 ceramic composites for such protection was achieved using the laser assisted in- situ reaction technique. As deposited alumina coatings were analyzed by scanning electron microscopy, energy and wavelength dispersive x- ray spectroscopy for their morphology and composition. The interface between the substrate and the laser deposited alumina coating were characterized for chemical composition using above techniques. The performance and microstructural and chemical compositions were studied after exposing the coated samples to high temperatures (>800deg.C) for long time durations.
OPTIMIZATION OF THE THERMAL SPRAY GUNS AND COATING PROCESSES USING NUMERICAL SIMULATIONIS: Shmuel Eidelman, Xiaolong Yang, Isaac Lottati, Science Applications International Corporation, McLean, VA 22102
Thermal Spray (TS) systems are low cost versatile methods of significantly improving the material properties of the base materials by coating them with the high performance materials. We show that the current TS systems are very inefficient in terms of energy and material utilization as well as in quality control. In addition, barrel erosion and coating lead to additional equipment maintenance costs and problems with coating consistency. We use a recently developed and validated three dimensional simulation capability for modeling TS systems gas and coating powder flow for the TS process analysis, and illustrate the roots of TS systems inefficiencies. The same capability can be used to design optimized TS gun systems, and for coating process optimization and control. Examples are given for TS process designs with improved performance and system efficiency. A reduced version of the developed numerical capability can be used for effective selection of the plating parameters and process control.
APPLICATION TO CERAMIC COATING AND SYNTHESIS OF SPHERICAL CERAMIC PARTICLES USING LASER SPRAY TECHNIQUE: Mamoru Okutomi, Koich Tsukamoto, Photon-process section, Electro-technical Laboratory, 1-1-4 Umezono Tsukuba ibaraki Japan
A laser spray method, which is melting and quenching of random shaped powder dropped perpendicularly to a focused CO2 laser beam in the air, has been developed. First, by observing using high speed camera, we investigate whether the ceramic particles in the ZrO2 -9 % mole Al203, [[gamma]]-Al203, TiO2 and Al203-Cr203 system are spheroid while passing through laser beam or not. The melting kinetics, residence time of particles inner laser beam and melting efficiency of particle with changing of laser power has estimated. Second, this rapid melting-solidification technique was applied to ceramic coating for improving several problems due to poor efficiency, production rates, controllability of the deposited structure. The properties of the coated layer are discussed with the melted particles passing through the laser beam.
STRUCTURAL CHANGES ON FLAME-SPRAYED ALUMINA AND CHROMIA: R.S. Lima, J.A.C. Martins, C.P. Bergmann, Department of Materials, School of Engineering, Federal University of Rio Grande do Sul. Av. Oswaldo Aranha 99/705, 90035-190 Porto Alegre RS, Brazil
Flame-sprayed substrate-free ceramic coatings of alumina and chromia were produced by applying the over preheated aluminum substrates around 200[[ring]]C. During the deposition temperatures above 500[[ring]]C were not allowed to avoid the substrate warpage. The coatings were easily detached from the substrate when the system coating-substrate reached the ambient temperature, due to the difference between the thermal expansion coefficient of the ceramic layer and the aluminum substrates. The coatings of alumina were reheated in air for periods of 2 hours at 1300 to 1700[[ring]]C. The coatings of chromia were reheated at 1500[[ring]]C for 2 hours. The structural changes occurred due to the heating on phase transitions, microstructure, true density, specific surface area for as-sprayed and sintered coatings were examined by X-ray diffraction, scanning electron microscopy, helium pycnometer and gas sorption analyzer respectively.
RESIDUAL STRESS, ADHESION AND THERMAL SPRAYED COATINGS: C. Richard, G. Beranger, Universtie de Technologie de Compiegne, Department de Genie Mecanique, URA 1505 du CNRS, 60206 Compiegne, France; J. Lu, Universtie de Technologie de Troyes, Department de Genie des Systems, Mecaniques,10000 Troyes, France
Most coatings are applied with a specific aim in mind, such as improving the
base material resistance to corrosion and wear, or providing a thermal barrier
against high temperatures. These aims can obviously be achieved if the coating
is properly bonded to the substrate. One important factor which contributes to
failure of plasma sprayed coatings is the residual stress produced during its
munufacture. This paper gives a review of the results on residual stresses
obtained in different coating systems (NiCrAlY metallic bonding layer, a Cr2O3
ceramic layer, and a WC-
cermet layer). To study the effect of the residual stresses on the properties
of the coatings (particularly on the adhesion of coatings to the substrate),
two techniques are used: a Vichers indention test is performed at the
substrate/coating interface (in order to determine, by a simplified model based
on mechanics concepts, "an interfacial toughness") and fout point bending test
assisted by an acoustic emission system.
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