Morphology and erosive wear of Fe–Cr coatings for gun bores deposited by physical vapor deposition

Bores of high‐performance guns are often protected by electrodeposited Cr coatings. As those coatings show severe microcracking during service, a study was conducted to assess the performance of binary Fe–Cr coatings deposited by physical vapor deposition. Samples mountable as the outlet nozzle of a vented vessel were coated with alloys ranging from very low to 100% Cr by evaporating Fe and Cr from two separate crucibles. The coatings were characterized with respect to morphology and mechanical properties and then subjected to a number of propellant gas pulses using two different propellants of 2449 and 3046 K flame temperatures, respectively. The wear rates were measured after each round. The results revealed a rather complex interrelationship between wear rate and composition/morphology of the coatings with the thermochemical properties of the propellant as an additional factor. Interestingly, alloys with only 20%–40% Cr showed erosion rates as low as pure Cr, but with a much reduced tendency to microcracking. The comparatively low Cr content improved the mechanical properties of the coating without impairing the protective quality of the oxides formed. The findings obtained are discussed in the light of Auger electron spectroscopy depth profiles of the gas/coating reaction layers.