1997 TMS Annual Meeting: Tuesday Session

ADVANCES IN COATINGS TECHNOLOGIES II: Session III

Session Chairperson: TBA

8:00 am

PULSED LASER DEPOSITION OF ELECTRONIC CERAMIC THIN FILMS: D.B. Chrisey, J.S. Horwitz, P.C. Dorsey, L.A. Knauss, R.C.Y. Auyeung, U.S. Naval Research Laboratory, Washington, D.C., 20375-5345

Pulsed laser deposition (PLD) is a unique physical vapor deposition technique that is making available high quality thin films of complex, multicomponent materials for the design and fabrication of advanced electronic devices and protective coatings. Single phase and epitaxial thin films can be deposited in situ. by PLD. Recent applications of PLD include high temperature superconductors, ferroelectrics, magnetoresistive materials and ferrites. Ferroelectric thin films grown by PLD are currently being developed into low loss, frequency agile microwave electronics which exploit the electric field dependence of the dielectric constant. More recently, colossal magnetoresistance with DRH/RH=0 ~100,000% has been observed in thin films of rare earth manganites deposited by PLD. These materials have applications in magnetic field sensing and recording as well as electrodes in solid oxide fuel cells and room temperature microbolometers. This presentation will show recent examples applying PLD to high quality electronics ceramic thin films growth for next generation devices.

8:35 am

THERMAL BARRIER COATINGS FOR AIRCRAFT ENGINES--A PRATT AND WHITNEY PERSPECTIVE: S. Bose, Pratt and Whitney, 400 Main Street, East Hartford, CT 06108

The gas temperatures in the turbine section of Aircraft Gas Turbine Engines are hundreds of degrees higher than the melting point of the materials of construction. Exposure to such high temperatures would result in structural failure of the materials from a variety of mechanisms. Yet, in modern engines, the components, generally made a nickel and cobalt based superalloys, survive for extended periods of time. This is accomplished by devising efficient air cooling of the components and by applying Thermal Barrier Coatings (TBCs) to the substrate alloy to reduce metal temperatures to safer levels. Combustor TBCs are processed with air plasma spray (APS) ceramic on APS metallic bond coat. Vanes, exposed to higher temperature and thermal load, require electron beam physical vapor deposition (EB-PVD) ceramic on FE/A1 laminates of different layer thicknesses were produced by PVD. TEM studies showed that as deposited microstructure depends on the ratio of the nominal thicknesses of the FE and A1 layers and on the actual layer thickness. For dfe:da1=0.4mm the microstructure consisted of nanocrystals of Fe/A1 solid solution with A2 or B2 structure and A13Fe. For dfe:dA1»44nm or 2.1mm:0.7mm laminated structures were produced. The laminates consisted of layers of Fe(A2-bcc) and of solid solution of Fe in A1 with B2 (ordered bcc) structure which was formed by interdiffusion between the Fe and A1 layers. Thermodynamic modelling showed that interdiffusion and interface reaction in the as deposited materials are closely related to the overall heat of mixing. The mechanical properties of the laminates will be related to their microstructures low pressure plasma spray (LPPS) bond coat. These TBCs have allowed the components to be operated at high gas path temperatures to meet thrust, efficient and life requirements of Pratt and Whitney's gas turbine engines. Details of Pratt and Whitney's experience on various aspects of TBCs will be discussed.

9:10 am

ANALYSIS OF THERMAL SPRAY METHOD FOR COATING NANOSCALE MATERIALS: Schmuel Eidelman, Xiaolong Yang, Science Applications International Corporation, 1710 Goodridge Drive, McLean, VA

Thermal Spray (TS) system allows delivery of the plating materials to the substrates at high velocities (on the order of 1 to 1.5 km/sec) and high temperatures. The total pressure of the particle impinging on the surface can reach 10 Gpa for some of the TS systems. Lower sintering temperatures and higher ductility of nanoscale materials open a range of attractive and unique possibilities for high rate deposition of nanostructured coatings. We use a recently developed and validated three dimensional simulation capability to model the TS systems' gas and coating powder flow for the TS process analysis, to illustrate the roots of currently used TS systems' inefficiencies, and to optimize and control the coating process. Examples are given for the TS process designs with improved performance and system efficiency. The use of numerical simulation will be especially crucial for the plating with nanoscale powders.

9:30 am

ROLE OF INTERDIFFUSION AND HEAT TREATMENTS ON THE ADHESION OF PLASMA SPRAYED NiCrAlY COATINGS: C.S. Richard, G. Beranger, Universite de Technologie de Compiegne, Department de Genie Mecanique, URA 1505 du CNRS, 60206 Compiegne Cedex, France; J. Lu, Universite de Technologie de Troyes, Department de Genie des Systemes Mecaniques, 10000 Troyes, France

During service blades and vanes of stationary gas turbines are subject to different kinds of loadings like mechanical and thermal stresses as well as corrosion, oxidation and erosion. Against these phenomena, plasma spraying coatings are frequently used to protect the componenets in the hot parts of these engines. The layers are commonly deposited by Atmospheric Plasma Spraying (APS) and by Vacuum Plasma Spraying (VPS). One of the main parameters in quality of a coating is its adhesion on a Ni-based superalloy substrate. This study focused on a NiCrAlY metallic bonding layer and its adhesion on a Ni-based supralloy substrate. It looks at the influence of different spraying methods (APS and VPS) and the influence of a post heat treatment on the adhesion of the coatings. In order to determine the interface toughness, a Vickers interfacial indentation test, based on fracture mechanics method, was performed. In APS and VPS cases, the residual stresses were evaluated by a step-by-step drilling method and these were taken into account in the adhesion parameters. The results were supplemented by a microstructural study of the interface in order to understand the role of interdiffusion on adhesion.

9:50 am

PLASMA SPRAYED ZIRCONIA BASED COATINGS FOR USE AS AN INSULATING LAYER IN DIE CASTING: M. Giannis, CAST, CSIRO Division Manufacturing Technology, Melbourne, Victoria, Australia

The casting of light alloys, such as aluminum, requires insulation in the form of a ceramic-based coating applied on the metallic die. This assists in the production of sound castings in gravity and low pressure die casting processes by preventing premature solidification. The currently used coatings are based on ceramic particles and sodium silicate binder slurry applied by spray-gun to the preheated substrate. These coatings were found to be fragile due to the highly porous network of binder an particles. Plasma spraying of ceramic zirconia-based particles was studied for possible use as a die coating. The coatings studied were characterized in terms of composition and microstructure. In addition, thermal properties were determined using experimental and simulation techniques to estimate the heat transfer coefficient at the die coating/casting interface. Zircona-based plasma sprayed coatings had high wear resistance and good heat transfer resistance and would therefore function as an improved die coating.

10:10 am

COATING PHASES OF COMMERCIAL GALVANNEALED COATINGS: Carlos Nelson Elias, Universidade Federal Pluminense, Av. Dos Trabalhadores 420, Vila Santa Cecilia 27260-740 Volta Redonda, RJ-BRAZIL, Jorge Alcala Vera, Institutio Militar de Engenharia, Pr General Tiburcio 80, 22290 270 Rio de Janeiro, RJ

Hot-dip galvannealed steel sheet has been increasingly used in the automotive industry and more recently it has been found that a zinc-iron alloy steel sheet, such as galvannealed would provide even better results. The galvannealed steel sheet is a product with good corrosion resistance, weldability and paintability. Therefore it has been used in the automotive and appliance industries. The properties of galvannealed steel are strongly influenced by the iron content of the coating, especially galling, corrosion resistance, welding and powdering. The galvannealed steel is predominately composed of delta phase. When the soft zeta phase is present in the surface of the coating, it adheres to the die and reduces the performance of steel sheet during deformation. When the hard and brittle gamma phase is at the interface steel-coating , the galvannealed coating fails by powdering. In this work we discuss the formation of Fe-Zn intermetallic compounds in the industrial galvannealed coating.

10:30 am BREAK

10:40 am

RECENT TRENDS IN ELECTROPLATING: Brian Am Manty, Concurrent Technologies Corporation, Johnstown, PA

This paper reports on recent trends and advances in electroplating as a surface finishing technology. It includes a description of environment and worker exposure regulations that have affected the industry. New developments in water and chemical recycling equipment and techniques have substantially reduced the amount of wastes generated during electroplating. Near-zero discharges are now technically and economically feasible for many electroplating shops. Several guidance documents are available to help electroplaters reduce wastes with simple, inexpensive techniques. Alternative electroplating processes and materials are also being developed for processes requiring the use of toxic materials. On-going programs within industry and the government are aimed at reducing the use of cadmium, chromium (hexavalent), lead and cyanide. There is a substantial increase in commercial formulations for alloy electrodeposits, especially where those alloys may be used as a substitute for more toxic coatings.

11:05 am

STRUCTURE AND PROPERTIES OF FUNCTIONALLY THICK CHROMIUM ELECTRODEPOSITS FROM A TRIVALENT ELECTROLYTE - A " GREEN " TECHNOLOGY: Christian E. Johnson, Jasper L. Mullen National Institute of Standards and Technology, Gaithersburg MD 20899

Chromium is widely used as an electrochemically applied coating on metal for wear resistance, to reduce friction, or for a desired appearance. In present
commercial electroplating processes, the chromium is deposited from electrolytes in which it is in the hexavalent state. With recent interest in seeking alternatives to the toxic Cr6+, a process has been developed to deposit thick chromium coatings from a non-toxic trivalent electrolyte. The coatings deposited from this electrolyte are an alloy of chromium-carbon-oxygen-hydrogen having an amorphous structure, as-deposited. However, with heat treatment they are transformed to a crystalline structure of chromium carbide in a chromium matrix. The hardness and resistance to wear increase with the transformation of this coating after heat treatment. The structure of the electrodeposited coatings, will be discussed. Property measurements of microhardness, wear and coefficient of thermal expansion will be discussed for the as-deposited and heat treated coatings.

11:35 am

COPING WITH UNINTENDED Cu ENRICHMENT DURING CONVERSION COATING OF MICROSTRUCTURALLY COMPLEX ALUMINUM: R.G. Buchheit, Sandia National Laboratories, Albuquerque, NM 87185

Copper is a major alloying element in engineering aluminum alloys. Cu is concentrated in second phase particles distributed throughout the alloy. The interaction of these particles with conversion coating solutions can result in enrichment of Cu on the treated surface. This enrichment has serious negative consequences on subsequent corrosion and adhesion properties. Direct examination using high resolution SEM shows that in 2024-T# Cu is segregated into large (2-6 micrometer) Al2CuMg particles. During surface finishing these particles experience severe dealloying and produce a fine dispersion of Cu-rich clusters that are distributed across the alloy surface facilitating galavanic corrosion during testing or service. Since redistribution of Cu across the surface is possible without ever oxidizing the Cu, mitigation schemes based on Cu complexing agent additions alone may be inadequate. However, mitigation schemes that utilize a Cu complexing agent and a sufficiently oxidizing solution can successfully prevent Cu enrichment and produce significant improvements in corrosion resistance.