Thermal–chemical–mechanical gun bore erosion of an advanced artillery system part one: theories and mechanisms

Thermal–chemical–mechanical gun bore erosion theories and mechanisms are described for an advanced artillery system and its associated laboratory-firing simulator system. Both high and low contractile chromium electroplated-coating types are examined. These theories and mechanisms are based on bore erosion measurements and characterizations for each of the coating types used in this live fired system and its simulator. This artillery system consists of a cannon, charge, projectile, and additives. Its simulator consists of a vented combustor, charge, and additives. Gun bores typically have an erosion barrier of 0.05–0.50 mm high or low contractile chromium electroplated coating on a nickel–chromium–molybdenum–vanadium high strength gun steel substrate. Gun system firing rates, zones, coating types, and coating thickness vary. The main types of measurements and characterizations are of gun system components, firing conditions, gas–wall kinetic thresholds from simulators, during-life erosion metallography and depth, and end-of-life erosion metallography, depth and chemistry. The initial gun bore erosion theories and mechanisms consist of combustion gases traveling down very fine radial cracks in the chromium coating and degrading the substrate steel. These fine cracks result from the plating process. This thermal, diffusion, and chemical degradation weaken the coating–substrate interface. Coating platelets eventually depart forming micro-pits that grow into gun tube condemning macro-pits. These erosion theories and mechanisms are subsequently used to develop erosion models, predictions, and mitigation efforts for each of the coating types used in this advanced artillery system and its simulator.