Date: Jul 15, 2010 Author: Joe Singleton Source: MDA (
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by Joe Singleton/jsingleton@nttc.edu
A technology initially designed to lubricate aircraft parts could lead to more durable nonstick cookware and prosthetic bone-repair implants.
Through a 2000 SBIR Phase II contract, MDA-predecessor BMDO funded Technology Assessment & Transfer, Inc. (TA&T; Annapolis, MD), to develop a low-friction, low-wear lubricant for the moving parts of missiles and aircraft.
After successfully developing a lubricant that met the SBIR contract's goals, TA&T researchers considered the overall commercial viability of such a product. Looking beyond the initial SBIR work, the researchers determined that the chemistry and techniques involved in making the lubricant could be used to develop hardened, wear-resistant coatings—not just for improving the durability of defense technologies, but also for improving cooking equipment.
The result of post-SBIR research led TA&T to develop quasicrystalline coatings using a process known as magnetron sputtering. Magnetron sputtering is a robust process that is capable of coating virtually any part of an object with a wide variety of materials. "Quasicrystalline" refers to metallic materials with unusual symmetrical patterns in their structure—substances that are very stable, but brittle. Quasicrystalline materials are defined as "quasi" because their hardness is between that of crystal and glass. Quasicrystalline structures consist of localized five-fold or ten-fold atomic symmetries which were previously forbidden by crystallographers. However, they exhibit long-range aperiodic structural order; hence, the term quasicrystalline. And magnetron sputtering—considered ideal for high-adhesion, high-quality, high-density thin-film coating—involves applying a magnetic field when making coatings to ensure the proper adherence and densities of particles. But use of magnetron sputtering for quasicrystalline materials can present a host of technical challenges, and typically quasicrystalline coatings are made with electroplating techniques or other manufacturing methods that involve plasma sprays.
TA&T's innovation lies in the formulation, processing, and preparation of the powder targets used in making the quasicrystalline coating as well as the sputter coating deposition conditions. The company has refined methods that solve two key problems associated with magnetron sputtering for quasicrystalline material—namely, the cracking and lack of stability that can occur when the coatings are exposed to high temperatures.
TA&T's quasicrystalline metal formulation is a combination of aluminum (Al), copper (Cu) or cobalt (Co), iron (Fe), and chrome (Cr) powders mixed in appropriate ratios to yield coatings with a 70-10-10-10 ratio. This four-metal mixture is known as a quaternary. The AlCuFeCr or AlCoFeCr compounds are good for coating things like frying pans and prosthetic joints because their chemical properties provide low friction, anti-adhesion, and corrosion resistance.
In TA&T's magnetron sputtering process (a technique that operates sort of like an atomic spray gun), frying pans, bone/joint replacements, or any other objects to be coated are placed on a carousel located in a vacuum chamber. Quasicrystalline quaternary material is added, followed by argon gas and electrical voltage. The voltage transforms the argon into a plasma (an ionized gas with high electrical conductivity), and the plasma spray flows into the chamber until the layers of the coating deposit at the requisite thickness (usually 5-10 microns). During the process, the positive argon ions are attracted to the negatively charged quasicrystalline target with enough energy to eject atoms from the material. The momentum imparted to the ejected quasicrystalline atoms end up depositing on whatever items are placed on the carousel in the vacuum chamber. The layer-by-layer sputtered deposition process continues until a coating of desired thickness is achieved.
Compared with other plasma-spray methods, quasicrystalline sputtering offers better adhesion, better corrosion resistance, and lower porosity, and the technique can produce thinner increments of film than other plasma sprays. TA&T President Larry Fehrenbacher said the average thickness of thin-film quasicrystalline sputtered coatings on frying pans is 5-10 microns, compared with more than 100 microns for other plasma methods. He further claims the adhesiveness and wear resistance of TA&T's coatings are superior to competitive variants.
TA&T has developed a practical, in-depth knowledge base between the processing methods used to deposit these coatings and their resulting properties. To date, TA&T has only tested its quasicrystalline coatings on frying pans in hopes of developing a better nonstick surface. According to Fehrenbacher, in tests the quasicrystalline-coated frying pans cooked great, had an attractive high-gloss look, and demonstrated no wear, but the company so far has not pursued commercial partners for the application. He said TA&T still is interested in marketing its coatings, and now is looking beyond the consumer cookware market. One such focus is the prosthetics market, as the coatings would be wear-resistant and accepted by human bodies, according to Fehrenbacher. The coating technology also has potential for use in any industrial or commercial equipment in which sticking, friction, wear, or corrosion are issues.
