Analysis of magnetron-sputtered tantalum coatings versus electrochemicallydeposited tantalum from molten salt

Prototype tantalum coatings, electrochemically deposited from a molten salt onto 20 mm interior bore steel liners, exhibited superior wear and erosion behavior to that of chromium coatings. The liners were subjected to cyclic exposures of high temperature, pressure, and an aggressive chemical enviro nment. X-ray analysis of the coatings revealed a low-hardness, randomly ori ented, body-centered cubic, alpha-phase tantalum. Formation of tantalum oxi des (predominantly Ta2O5), swaging due to the low-hardness of the coatings, a 2 mu m layer consisting of tantalum and carbon at the tantalum-steel int erface, and surface compressive residual stresses were observed. Cylindrica l magnetron sputtering systems were constructed to coat 45 mm interior bore steel cylinders to protect from wear and erosion. X-ray diffraction, scann ing 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. (C ) 1999 Elsevier Science S.A. All rights reserved.