Metallurgical post-mortem analysis of the cannon caliber electromagnetic gun: rails and insulating sidewalls

A post-mortem tear down analysis was performed on the chromium-copper rails (alloy C18200) and alumina insulating sidewalls (AD-96) of the Cannon Caliber Electromagnetic Gun (CCEMG) after it had launched forty-nine aluminum alloy 7475 slugs or sabots with projectiles. The rails did not exhibit signs of gouging, however, a layer of aluminum from the armatures, approximately 13 microns thick, was deposited on them. The hardness and conductivity values of the rail material remained consistent along the length of the rails. The alumina sidewalls were cracked at the breech end of the gun from the start of the gun to a distance of 61 cm. Most of the cracks were due to the armatures cutting notches in the ceramic and exceeding the critical crack size of the material. Molten aluminum was found in the cracks suggesting that the cracks had formed in service and not due to the tear down procedure. Aluminum had deposited on and adhered to the alumina sidewalls as well as the rails. Despite sustaining some damage to the sidewalls and a buildup of aluminum on the rails and sidewalls the gun functioned until its decommissioning.