Nitriding ferrous materials for enhanced thermochemical stability

A nitriding process and structure that improves thermochemical stability and safeguards steel and other ferrous materials exposed to combinations of high- temperature, high-pressure, and corrosive ambient environments


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The US Army Research Laboratory (ARL) is a national scientific and engineering leader in weapons, protection, and materials technologies, and is keenly focused on innovations to prevent or minimize thermochemical erosion of substrate materials leading to pitting, cratering, cracking, and failure.

ARL researchers have developed two new approaches to protecting steel and other ferrous materials: one is static and the other is dynamic.  The static approach creates a layer of low-nitrogen iron nitride directly on the steel surface, where the nitrogen diffuses into and reacts with the iron lattice.  The layer can be formed using any of several known deposition techniques or by nitriding the steel.  A refractory material such as chrome can be deposited overtop of the nitride layer, which has been shown to reduce cracking within the chrome layer.

The dynamic approach involves combusting a high-nitrogen content propellant or fuel so that the nitrogen in the combustion products reacts with the steel substrate to form a protective iron nitride surface layer.  This is particularly useful for protecting the underlying metal in a steel/chrome gun barrel system. When cracks develop in the overlying chrome layer, the exposed underlying steel is still protected.  Hence, in guns, this dynamic protective process would occur each time the ammunition containing the described nitrogen content is fired.

The inventor estimates that either the static or dynamic approach could extend barrel life by 10-15%. He further estimates that barrel life can be extended by 20-30% if the inventions are utilized together.

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