Screening Gun Barrel Coatings' Response to Combustion Gases

A 37-mm blowout gun, long used at BRL to study gun barrel wear, was evaluated as a screening device for testing coatings or platings on gun steel. It was shown that selection of charge mass, propellant flame temperature and rupture pressure made it possible either to remove the plating in one shot or to leave the plating virtually intact after ten shots. An erosion profile similar to plated large caliber guns was duplicated with a nozzle coated with sputtered chromium, i.e., virtually no erosion for several shots followed by flaking of the chromium from the surface. Several alloys sputtered onto nozzles and low- contraction, electroplated chromium were tested. Sputtered coatings containing tantalum warrant further investigation due to the method of the coating failure, while the low-contraction chromium did not appear any better than thicker, standard high-contraction, electroplated chromium.