NANOSTRUCTURED COATINGS

Maurice Gell
Department of Metallurgy and Materials Engineering
University of Connecticut
Storrs, CT 06269

Nanostructured materials and coatings offer the potential for significant improvements in engineering properties based on improvements in physical and mechanical properties resulting from reducing microstructural features by factors of 100 to 1000 times compared to current engineering materials. The potential benefits include higher hardness and strength in metals and cermets resulting from reduced grain size and slip distance, respectively. In ceramics, higher hardness and toughness may be accomplished with reduced defect size and enhanced grain boundary stress relaxation, even at ambient temperature. Diffusivity is greatly increased, associated with a larger volume of grain boundaries. Thermal conductivity may be reduced because of enhanced phonon scattering from grain boundaries and other nanoscale features.

In engineering materials, there is usually a toughness tradeoff with strength and hardness. The possibility exists that this tradeoff will occur at higher levels for ceramics and cermets. This is believed to be the explanation for improved wear and abrasion resistance of monostructured WC-Co. Fischer has shown that the wear track is much smoother and narrower in nanostructured WC-Co. This has important implications for a wide variety of wear-, erosion-, and abrasion-resistant coating applications.

Thermal barrier coatings (TBCs) are used extensively in gas turbine applications to insulate superalloy turbine blades and vanes from the hot gas stream. There is a need for thermal barrier coatings with improved durability and performance. In thermal sprayed TBCs, failure of the coating occurs by spallation in the ceramic "splat" boundaries near the ceramic-to-metal interface. It should be possible to strengthen the boundaries by refining the structure to the nanoscale. In addition, it may be possible to develop TBCs with improved performance, by reducing thermal conductivity resulting from enhanced phonon scattering at grain boundaries. Both of these concepts are being evaluated in a recently awarded Office of Naval Research contract to the University of Connecticut.

The coatings industry is a major industry in the United States and worldwide. Coatings are needed to prevent wear, erosion, and corrosion, and to provide thermal insulation. For both commercial and military applications there is a need for coatings with improved durability and performance. Nanostructured coatings show promise based on initial laboratory trials. Durability improvements of 3 to 5 times can be projected for a number of coating applications. It will be necessary to demonstrate the technical and economic viability of these coatings on a commercial scale. To accomplish demonstration and implementation of this technology in a timely, cost-effective manner, a disciplined concurrent engineering approach is recommended.

Nanostructured Materials -- Potential Benefits




Increased Hardness and Toughness


Wear Resistance of Conventional and Nanostructured WC-Co Composites


Wear Surface Morphology of
Conventional and Nanostructured WC-Co Composites




Improvements Afforded by Nanostructured TBCs

Current 7 YSZ Coating



Nanostructured 7 YSZ Coating


Calculated Thermal Conductivity of 7 YSZ
as a Function of Temperature and Grain Diameter




Nanostructured Materials -- Processing Methods


			Sputtering Chamber



Critical Issues for Manufacturability

Critical Control Parameters

Barriers to Progress

Approaches to Overcome Barriers

Nanostructured Materials -- Coating Technology Plan


Nanostructured Materials -- Gas Turbine Engine Materials Requirements



	Thrust-Vectoring P&W F100 Engine	High-Speed Civil Transport

Nanostructured Materials -- Gas Turbine Engine Applications


Nanostructured Materials -- Coatings Opportunities


Nanostructured Materials -- Technology Assessment

Technology Assessment

Nanomaterials Technology Requirements

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Published: January 1998; WTEC Hyper-Librarian