Properties of Thick Sputtered Tantalum Used for Protective Gun Tube Coatings

摘要

Thick tantalum coatings were deposited on the bore surfaces of 25-mm inner diameter cylindrical gun steel substrates using a high-rate triode- sputtering apparatus. Sputtering parameters affecting the tantalum phase and microstructure were investigated. Prior work has indicated that the sputtering gas species and substrate temperature during deposition affect the characteristics of the tantalum coatings. In the work presented here, we report on experimental studies aimed at evaluating additional phase and microstructural effects resulting from changes in sputtering gas species and substrate bias during the deposit. Tantalum deposits of 75 to 140 micrometers thickness were evaluated using x-ray diffraction, optical microscopy, and microindentation hardness measurements. Coatings deposited using krypton gas, a 200 deg C substrate temperature, and 3.5 mTorr gas pressure also showed little variation when deposited at substrate biases ranging from 50 to 150 V. However, the tantalum coatings produced under similar conditions with an unbiased (floating) substrate were found to be the beta phase of the material and had a columnar microstructure. Beta-phase tantalum was produced at low substrate biases (