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, the Ballistic Missile Defense Organization (BMDO), a predecessor of the Missile Defense Agency (MDA), funded the Annapolis, MD-based company Technology Assessment & Transfer, Inc. (TA&T) 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, the TA&T researchers determined that the chemistry and techniques involved in making the lubricant could be used to create 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, which 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 structures consist of localized five-fold or ten-fold atomic symmetries which were previously forbidden by crystallographers. They, however, exhibit long-range aperiodic structural order. Quasicrystalline materials are defined as quasi because their hardness is between that of crystal and glass.
Magnetron sputtering — considered ideal for high-adhesion, high-density thin-film coating — involves applying a magnetic field when making coatings to ensure the proper adherence and densities of particles. Use of magnetron sputtering for quasicrystalline materials, however, can present a host of technical challenges, and typically quasicrystalline coatings are made with electroplating techniques or other manufacturing methods that involve plasma sprays.
How it Works
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 objects 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, 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 attract 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.
Where it Stands
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. In tests, according to Fehrenbacher, the quasicrystalline-coated frying pans cooked well, 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 challenges. TA&T now seeks potential customers or strategic partnerships to help move its product to market.
For more information on TA&T's quasicrystalline coatings, visit http://info.hotims.com/34453-522. (Source: Joe Singleton/NTTC; MDA TechUpdate, Missile Defense Agency, National Technology Transfer Center Washington Operations)