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A Fast Approach to Coating

If you heard that something called "Cold Spray" was originally developed at the Institute of Theoretical and Applied Mechanics of the Russian Academy of Sciences in Siberia you might think that we are talking really cold.

If you heard that something called "Cold Spray" was originally developed at the Institute of Theoretical and Applied Mechanics of the Russian Academy of Sciences in Siberia you might think that we are talking really cold. Yet in point of fact, this coating process, which came to the U.S. in 1994 (it was invented 10 years prior to that), actually involves the coating materials being applied when they are at or near room temperature. (Specifically, the coating particles are at from 0oC to 700oC, below their melting temperature.)

A more appropriate name might be "Fast Spray" because the spraying occurs such that the 10- to 50-micron particles are traveling at a velocity of 500 to 1,500 meters per second when they hit the substrate that is consequently coated.

Research on the application of Cold Spray is underway at the Sandia National Laboratories in Albuquerque, NM, where there is a consortium of compnies involved. It includes Alcoa; DaimlerChrysler; Ford Motor; The Jacobs Chuck Manufacturing Co.; Pratt & Whitney; Praxair; Siemens/Westinghouse; Ktech Corp. The last-named company, which is based in Albuquerque, was established in 1971 as a research and engineering firm to study nuclear weapons effects. Subsequently, it has widened its areas of interest such that it employs Dr. Anatolii Papyrin, who holds the patent for the cold gas spray process. (He and his colleagues did the work at the Russian Academy of Sciences.)

Apparently, when the metal particles (metals that can be used include iron, stainless steel, nickel, copper, aluminum, molybdenum, titanium, and various alloys) hit the metallic or dielectric substrate, there is a disruption of the thin metal-oxide films on the surfaces of both the particles and the substrate so that there is intimate contact of the materials at an atomic level. The advantage of this approach as compared with the more common thermal (i.e., arc or flame processes) spray method is that the various effects that can be caused by high heat (e.g., oxidation, vaporization, residual stresses, debonding, gas release) are avoided.

There are a variety of purposes that this method can be deployed for, such as strengthening/hardening; providing wear resistance; providing corrosion resistance; metalizing plastics; joining, or sealing, parts; and providing electrical insulation for metals, ceramics, plastics.

According to Sandia researcher Mark Smith, "Cold Spray has some significant advantages as a coating and fabrication tool, and it provides capabilities not previously possible. It's a new enough technology that we don't yet know all the possible applications, but it has the potential to make truly revolutionary changes in the way some products are manufactured."

The system that is used to perform the process consists of a gas control module that regulates the high-pressure gas; a gas heater; a powder feeder; the supersonic nozzle; and a data acquisition and control system. According to the people at Ktech, there is no "standard" system for cold spray operations; however, when producing systems, they use standard components.

Although the particles are small, a high deposition rate can be achieved; the power feedrate can be up to 30 lb. per hour.

One of the evident application areas for automotive is in coating cylinder bores. Another is to deposit layers of conductive metals onto substrates for use in underhood automotive electronics.