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, PM Room: B1
February 5, 1996 Location: Anaheim Convention Center
Session Chairpersons: Ashok Kumar, Department of Electrical Engineering, University of South Alabama, Mobile, AL 36688; Jacob J. Stiglich, P.O. Box 206, Sierra Madre, CA 91025
GRADED Ni-Al2O3 COATINGS VIA ELECTRODEPOSITION:
S.W. Banovic, C.M. Petronis, Barmak, K., Marder, A.R. Department of Materials Science and Engineering, Lehigh University, Bethlehem, PA 18015
Functionally Graded Materials (FGMs) are being investigated for use as thermal barrier coatings (TBCs) in advanced gas turbine systems. The principle failure mechanism in conventional TBCs is the spallation of the ceramic top coat from the metallic bond coat due to dissimilar thermal expansion coefficients. In order to eliminate this problematic interface, FGMs are being evaluated. A model system of codeposited metallic nickel matrix with second phase alpha-alumina particulates (Ni-Al2O3) was studied in an initial effort to produce a graded structure. Electrodeposition process variables were investigated and optimized to produce Ni-Al2O3 composite coatings with varying Al2O3 volume percents. Through manipulation of these process variables, a discretely graded structure of Ni-Al2O3 ranging from 0 to 35 volume percent alumina particulate in the deposit has been produced. Light Optical Microscopy (LOM), Scanning Electron Microscopy (SEM), and Quantitative Image Analysis (QIA) techniques were used to characterize the electrodeposited microstructure in detail. Microhardness tests were performed to evaluate the mechanical properties of the electroplated coatings. The relationships between the microstructure and microhardness were analyzed.
2:20 pm
EROSION OF THERMAL SPRAY MCrAlY-Cr3C2 CERMET COATINGS: K.J. Stein, B.S. Schorr, A.R. Marder, Energy Research Center, Lehigh University, Bethlehem PA 180l5
Solid particle erosion (SPE) is a serious problem for the electric power industry, costing an estimated $150 million a year in lost efficiency, forced outages, and repair costs. In an attempt to reduce the damage caused by SPE many industrial users have turned to high velocity oxy fuel (HVOF) cermet coatings. The ceramic content of these cermet coatings needed for optimum erosion resistance is still unclear. The current work investigated the erosion resistance of FeCrAlY-Cr3C2 and NiCr-Cr3C2 cermet coatings with carbide levels ranging from 50-100% (in the pre-sprayed powder). The as sprayed coating microstructures were fully analyzed using light optical microscopy (LOM), scanning electron microscopy (SEM), x-ray diffraction, and microprobe analysis. This line of testing revealed the carbide levels in the starting powder are much higher than in the final as sprayed coating. It appears that the carbides react with the HVOF jet resulting in the formation of various oxides. Erosion testing was carried out using a particle accelerator apparatus set at 40 m/s, 80 g/min, and 400[[ring]]C with 300um A1203 particles for both 30[[ring]] and 90[[ring]] impact angles. Upon erosion testing of the sprayed coatings it was discovered that the erosion rate decreased as the carbide content, and overall hard phase content (oxides and carbides), was reduced for 90ø impact. In addition the erosion rate remained fairly constant regardless of carbide content, or hard phase content, for 30[[ring]] impact.
2:40 pm
CUBIC CALCIA STABALIZED ZIRCONIA COATINGS WITH SPUTTER DEPOSITION: Mahendra Pakal, Ray Y. Lin, Departrnent of Materials Science, University of Cincinnati, M.S. 12, Cincinnati, OH 45221; Heather Walls, Crucible Magnetics, Magnet Drive, Elizabethtown, KY 42701
Calcia stabalized zirconia films were deposited on the surface of <111> silicon wafers using RF magnetron sputter deposition. Deposition was carried out at substrate temperature varying between 80deg.C and 900deg.C. X- ray diffraction results show that all films consist of cubic zirconia. The fracture surface morphology of the films were studied using scanning electron microscope (SEM). Depending on the deposition temperature, the structure of the film is either columnar or equiaxed. The transition temperature from columnar structure to equiaxed structure was found to lie between the T/Tm ratios of 0.39 and 0.43. The microhardness of the films is found to increase deposition temperature. This is due to probably that the hardness of ceramic materials decreases with the increase in the defect concentration.
3:00 pm
PHASE COMPATIBILITY OF ZrO2-ZrSix-SiO2 AT 2073 K: Charles A. Odegard, Mario Cuen, Arturo Bronson, Materials Research Center of Excellence (MRCE), 321 Burges Hall, The University of Texas at El Paso, El Paso, TX 79968
Multiphase compatibility has been investigated for the reaction couple zirconium oxide/zirconium silicide/silica at 2073 K in air. The multiphase system was assembled by encapsulating zirconium disilicide in a quartz capsule. In a previous study of this system at 2273 K, annealing resulted in an inner core consisting of liquid zirconium silicide and an interdiffusion zone. The interdiffusion zone developed between the liquid silica layer and liquid silicide was composed of zirconia precipitates with liquid silicide globules dispersed in a liquid silica matrix. The microstructural features and their consequences on the oxygen flux of the zirconium silicide/oxide coating will be discussed.
3:20 pm BREAK
3:30 pm Invited
EXPERIENCE IN SEEKING HOT CORROSION-RESISTANT STABILIZERS FOR ZIRCONIA: Robert L. Jones, Chemistry Division, Code 6170, Naval Research Laboratory, Washington, DC 20375-5342
This paper summarizes the results of a research effort aimed at identifying hot corrosion-resistant stabilizers for use in zirconia thermal barrier coatings (TBCs) for engines. Among the oxides investigated were TiO2, CeO2, Y203, MgO, Sc2O3, In2O3 and SnO2. A brief overview of the hot corrosion of zirconia TBCs is given to illustrate the rationale used in evaluating the hot corrosion performance of the candidate oxides.
3:55 pm
STRUCTURE AND PROPERTIES OF SPUTTER-DEPOSITED BN THIN FILMS: R. Capelletti, Istituto Nazionale di Fisica della Materia; Dipartimento di Fisica, Universita' di Parma, Parma, Italy; M. Elena, CMBM, 38050 Povo (TN), Italy; D. Ielmini, Dipartimento di Ingegneria Nucleare, Politecnico di Milano, 20133 Milano, Italy; A. Miotello, Istituto Nazionale di Fisica della Materia; Dipartimento di Fisica, Universita di Trento, 3 8050 Povo (TN), Italy; P.M. Ossi, Istituto Nazionale di Fisica della Materia; Dipartimento di Ingegneria Nucleare, Politecnico di Milano, 20133 Milano, Italy
This paper presents results obtained on BN thin films deposited with an RF magnetron sputtering machine, adopting RF bias of the samples and process atmospheres composed of argon, or of an argon-nitrogen mixture. Comparisons with films produced by applying DC bias are also made. The techniques used to characterize the films, which were deposited on silicon substrates, were IR spectroscopy, AES, SEM and nanoindentation, providing information on structure, composition microstructure and mechanical properties (hardness and Young's modules). By a suitable choice of experimental parameters, both hexagonal and cubic phases were produced. The type of bias (DC or RF) has a major influence on the film structure of the samples. Film composition, which is significantly influenced by process atmosphere is also important for determining the relative abundance of the hexagonal and cubic phases.
4:15 pm
PROCESSING AND CHARACTRIZATION: PLASMA ASSISTED-CVD DIAMOND FILMS: Mohit Sisodia, T.V. Rajan, Dept. of Metallurgical Engr., Malaviya Regional Engr. College, Jaipur-17, India
Recent advancement in surface modification by high temperature coating technology that allows the chemical vapour deposition (especially the plasma assisted) of diamond films on many different materials. Present paper critically reviews the morphologies/physical properties of Diamond and Diamond like carbon (DLC) films produced by various techniques like Magnetron sputtering, microwave plasma, laser assisted with much emphasis on Plasma assisted - CVD along with its characterization and process variables. Besides it, Japans latest technique of Stable Plasma process are also discussed. Due to the high temperature properties such as melting, solid-solid equillibria and thermal expansivity by laser heated cell, these films have been used extensively for fabrication of high temperature, high power and high frequency semiconductor/electronics devices. Thermal imaging windows and mechanical components of industrial practices, are also studied at length.
4:35 pm
MICROSTRUCTURE OF LASER CLAD ZrO2- (Ni ALLOY) COMPOSITE COATING: Y. T. Pei, T.C. Zuo, Institute of Applied Lasers, Department of Physics, Beijing Polytechnic University, Beijing 100022, China
The microstructure of laser clad 60vol.% ZrO2 (partially stabalized with 2mol% Y2O3) plus 40vol.% Ni alloy composite coating on stainless steel 4Crl3 was investigated by scanning electron microscopy, electron probe microanalysis, X- ray diffraction, energy- dispersive X- ray analysis, and microhardness tests. A stratification is observed in the clad coating which consists of a pure ZrQ clad layer in the outer region and a bonding zone of Ni alloy adjacent to the substrate. The pure ceramic layer exhibits columnar ZrO2 dendrites growing from the ceramic layer- bonding zone interface. This ceramic layer is composed of metastable x1- ZrO2 phase and a very small amount of m- ZrO2 phase distributed along the boundary of tl grains. The high heating and cooling rate caused by laser cladding restrains the t- >m phase transformation in the ceramic layer. The bonding zone of u-Ni alloy shows the multi- phase structure of primary ll- Ni dendrites and interdendritic eutectics, and have good metallurgical characteristics between the clad ceramic layer and the substrate.
4:55 pm
ZnO COATINGS GROWN BY PULSED LASER DEPOSITION: M. Baleva, A. Chalkov, E. Mateena, Faculty of Physics, Sofia Unviersity, Sofia 1126, Bulgaria
Abstract not available.
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