CURSORY DEVELOPMENT OF AN NDI METHOD FOR INTERNAL COATINGS ON ARMY GUN BARRELS

摘要

The Army has researched the concept of utilizing cold spray coating technology as an alternative to the conventional electroplated chromium coating within 20mm gun barrels. This project was undertaken as part of the Army's Toxic Metal Reduction program to remove hexavalent chromium from the manufacturing process, and involves the creation of tantalum-10% tungsten "donor tubes" for explosive bonding to the inner gun barrel. A major concern of any internal coating process (such as the interior of a gun barrel) is the integrity of the final product, since it is not a location that is easily inspected. As such, a nondestructive inspection method was developed, allowing successful evaluation of the interior gun barrel coating. The research involved a high-frequency ultrasonic inspection whereby the elastic waves were transmitted from the exterior. The equipment consisted of contact and immersion probes with center frequencies of ～10 MHz connected to a pulser/receiver system with variable duty cycles. The analog time-amplitude signals were acquired with a high-speed (2 GHz) digitizing oscilloscope and evaluated/stored in a PC. The test arrangement was used to measure the average liner thickness as a function of distance along the barrel. Results comparing well-bonded and delaminated samples were also achieved.