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Scientists at the Army Research Laboratory have developed an iron nitride coating with a nitrogen content of less than 20%. The patented technology is available via license agreement to companies that would make, use, or sell it commercially.
Gun barrels are often comprised of iron, steel or other ferrous alloys. They are frequently exposed to various combinations of high temperatures, high pressures, and corrosive environments. These conditions can cause thermochemical erosion, leading to pitting, cracking, and failure.
Ignition of a propellant charge creates combustion products which propel a projectile through the barrel. These combustion products can be in the form of ions, radicals or neutral species, and can cause a chemical reaction to occur. For example, carbon monoxide, one of several reactive combustion products, can cause carburization of the steel.
There is a need for methods of stabilizing steel alloys against thermochemical corrosion that are simple to implement and don’t interfere with device function. ARL scientists have developed a method for depositing a layer of a low-nitrogen, iron nitride on the surface of the gun barrel via chemical or plasma-assisted vapor deposition, evaporation, sputtering, or photochemically activated deposition.
The iron nitride’s atomic percentage of nitrogen is relatively low, at no more than 20 percent. These low-nitrogen coatings have a higher melting point than standard iron nitride coatings containing at least 33% nitrogen. Thus, the new layers are more suitable for extremely high-temperature environments with a melting point over 1,600° K. In gun barrels with high levels of friction, it may be advantageous to include a layer of a high-hardness refractory material atop the nitride layer.
The invention has specific utility for protecting gun barrels but also applies to turbines, internal combustion engines, drilling equipment, aerospace systems and chemical reactors that operate in extreme conditions.
- Nitride layer dramatically prolongs the service life of the gun barrel by preventing the carburization and subsequent melting point decrease of the steel, which could lead to pitting, erosion, and failure
- Nitride layer enhances the stability and compatibility of an overlying chromium protective layer and prevents cracking due to hardness mismatch
- Specifically tested for gun barrels, but applicable to any device operating in extreme temperature and pressure conditions
- Businesses can commercialize the technology by licensing U.S. Patent 7,650,710 from the Army
- This U.S. Patent 7,650,710 is related to U.S. Patent 7,669,358
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