Corrosion is a universal problem for engineers. Every industry, to some degree, has to combat the environmental degradation of its products. Not every industry, however, has to deal with the demanding service conditions of an artillery piece such as a Howitzer.
Large caliber weaponry has what might be considered a rough life, and the breech spindle, which seals the chamber to hold pressure during firing, is right in the thick of it. Corrosive firing byproducts in combination with extreme temperatures and pressures have led to premature failure of these components due to accelerated corrosion.
To extend the service life of the spindle, an engineering collaboration led by a team at the U.S. Army Research, Development and Engineering Command (RDECOM) is researching advanced coatings and processes. The research, headed by project officer Maira Senick and technical lead Chirstopher Mulligan, is seeking to identify a suitable replacement for chromium, the current standard in breech spindle design.
As described by Mulligan, a materials engineer, "A lot of times when you're trying to improve performance or eliminate hazardous materials, you end up with a more expensive process. Here, we're a [sic] saving a significant amount of money over the life cycle of the weapon with minimal to no increase in production cost."
That significant amount of money is stated to be something like $2M or more. A welcome improvement for sure, but there is more than cash being considered in the project.
The current technology involves electroplating chromium onto the spindle. Although tightly controlled, a highly carcinogenic byproduct, hexavalent chromium, is produced during the process. The proposed replacements are aimed at reducing the environmental impacts.
< The work was initiated in response to the inadequacy of current technology. The engineers sought to address 10 key aspects they aim to improve including corrosive, thermal, and mechanical properties. Among the processes being considered are High Power Impulse Magnetron Sputtering, Accelerated Plasma Arc, and Electroless Nickel Plating, as well as newly-developed coating known as Carbonyl deposited through chemical vapor deposition (CVD).
To test the coatings, the spindle is subjected to a round of firing, 30 days of weathering in “swab water” (a corrosive propellant byproduct bath), a second round of firing and a final weathering cycle. The team is hoping to identify and deploy a new coating within 6-12 months.
Images courtesy of US Army