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Interior Physical Vapor Deposition Coatings

One of the unique capabilities within the Energy and Engineering Division of the Energy Sciences and Technology Directorate is Interior Physical Vapor Deposition (IPVD) coating technology. The IPVD technique has been developed at PNNL over the past five years, and some of its applications are now nearing commercial implementation. The IPVD coating technology is applicable to a variety of coating and substrate materials with a unique capability of producing smooth and uniform coatings on the inner surface of small-diameter cylindrical components or other confined geometries. The technique has been used to deposit reproducible coatings on the inner surface of tubes as small as 10 mm in diameter in lengths up to 3.8 m. For larger-diameter tubes or pipes in which radiant heating of the substrate from the source filament is impractical, separate resistive or inductive heating of the substrate to the desired temperature is used. The image at above demonstrates one possible coating microstructure, showing multiple layers on the inner surface of a small diameter tube.

Many applications in which wear, corrosion or erosion cause design challenges involve geometries that are not amenable to traditional coating techniques. To address these challenges, exotic materials or sub-optimal design solutions are typically employed. The IPVD coating technique offers a potential alternative to these practices, enabling performance improvement and/or manufacturing cost reduction In the nuclear power industry, the process could be used to deposit corrosion- and erosion-resistant coatings in steam generator tubes, condensers, and valve and pump bodies. There also may be potential applications in producing mechanically-compliant coatings on the inner surface of cladding tubes or burnable absorber coatings in cladding or fuel channels. In the automotive industry, the technique could be used to deposit a hard-facing iron-, nickel- or chromium-aluminide coating on Al-alloy engine block cylinder walls to improve fuel economy and engine performance and decrease manufacturing costs. In the defense industry, the IPVD technique may offer an environmentally-friendly replacement for hexavalent-chromium electroplating in military gun barrels for wear- and corrosion-resistance. Other market opportunities may exist in the chemical processing and well drilling industries. Most of the potential commercial applications for the IPVD technique involve geometries that are less demanding than the application for which it was developed. Also, most potential commercial applications involve materials that may be evaporated from the solid state, further simplifying the process. The technique lends itself well to automation, and it is extremely flexible in terms of coating materials and geometry. Process times are short, allowing high throughput, no hazardous feed materials are required, and no hazardous effluents are produced. Each specific application will require fine-tuning of the filament design and process parameters, but the fundamental science behind the process is well understood and the path forward is essentially a matter of engineering.

Two IPVD systems used for coating development are currently housed in the Material Sciences Laboratory (Building 326) in the Hanford 300 Area north of Richland, Washington. One of the systems (shown at left) is used for process development on small-diameter tubes in lengths up to three feet. For shorter lengths, another system exists that can accommodate samples with larger diameters. The shorter system also is suitable for producing evaporative PVD coatings on exterior surfaces of moderate-sized samples. Two other IPVD systems have been constructed, one suitable for development purposes that is capable of handling tubes in lengths up to 4 m, and another production system built for a specific application that coats four 4-m long tubes simultaneously in each of three vacuum chambers. System control ranges from manual on the developmental systems to fully automated on the production system. Experience has been gained with a variety of coating and substrate material systems, including aluminum on 300- and 400-seriesstainless steels, aluminum on alloy steels, nickel on zircaloy, nickel on Al-base alloys, and iron on Al-base alloys.

For more information:

Contact David Senor (509-376-5610) for more information regarding the specific capabilities of the Interior Physical Vapor Deposition coating technology.