Analysis of Molten Salt and Sputter-Deposited Coatings on Steel Cylinders

摘要

Prototype tantalum coatings, electrochemically deposited from a molten salt onto 20-mm interior bore steel liners, exhibited superior wear and erosion behavior compared to chromium coatings. The liners were subjected to cyclic exposures of high temperature, pressure, and an aggressive chemical environment. X-ray analysis of the coatings revealed a low-hardness, randomly- oriented, body-centered-cubic, alpha-phase tantalum. Formation of tantalum oxides (predominantly Ta2O5), swaging due to the low-hardness of the coatings, a 2-micrometers layer consisting of tantalum and carbon at the tantalum/steel interface, and surface compressive residual stresses were observed. Cylindrical magnetron sputtering systems were constructed to coat 45-mm interior bore steel cylinders to protect them from wear and erosion. X-ray diffraction, scanning electron microscopy, photomicrography, and hardness analysis of several sputter-deposited tantalum specimens revealed coatings consisting of soft body-centered-cubic alpha-phase and hard tetragonal beta-phase tantalum.