NANOSTRUCTURED COATINGS

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.

			Sputtering Chamber

• Materials Availability

• Materials Reproducibility

• Process Reproducibility

• Materials and Manufacturing Cost

• Selection of deposition process(es)

• Choice of processing parameters for compositional and microstructural control

• Selection of materials and deposition parameters for interface control in multilayered structures

• Selection of materials and deposition parameters to enhance thermal stability

• Materials availability

• Multi-lot properties data

• Thermal stability

• Cost-effectiveness

• Establishment and substantiation of scientific drivers

• Applications-driven research

• Disciplined concurrent engineering

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

Technology Assessment

• Quantum improvement in variety of properties
  • Hardness/strength
  • Strength and toughness
  • Thermal conductivity

• Properties generated on subscale specimens for simple alloys/ceramics

Nanomaterials Technology Requirements

• Applications-driven cost/benefit/risk analysis

• Synthesis of engineering alloys

• Generation of engineering properties

• Demonstration of cost-effective manufacturing feasibility

• Some early successes