Thermal Damage and Shear Failure of Chromium Plated Coating on an A723 Steel Cannon Tube
Abstract
Degradation of the electroplated chromium coating at the bore of A723 steel cannon barrels is characterized here following cannon firing and used to model the coating failure process. Transient thermal stresses due to firing are calculated using one-dimensional heat flow analysis and used as input to a shear failure model of the coating/substrate couple. The cracking array that develops in the coating and substrate with repeated thermal cycles, the configuration of cracked segments of the coating, and the elevated temperature properties of the coating and substrate are considered in the shear failure model. Accordingly, the coating failure behavior predicted from the model is compared with the observations of coating failure mechanisms from actual fired cannon tubes. The results of the investigation show that growth of hydrogen cracks in the steel under the chromium coating allows broadening of cracks in the coating, and subsequent shear failure of the steel under a segment of coating due to transient thermal stresses. Loss of coating segments then leads to rapid hot gas erosion of the steel and loss of function of the cannon tube. The objective is to model the final critical phase of thermal damage imparted to a chromium coating on a cannon bore that leads to the separation of a segment of coating.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 01, 1999
- Accession Number
- ADA367743
Entities
People
- Anthony P. Parker
- John H. Underwood
Organizations
- United States Army Armament Research, Development and Engineering Center