Physical vapor deposition of chromium and iron

Chromium and iron films of 10–50μm thickness were deposited on beryllium substrates by electron-beam evaporation. Deposition rates varied from 35 to 425 Å/s. Substrate temperatures ranged from 300° to 650°C. The relationships between coatings characteristics and substrate temperatures, deposition rate, and angle of vapor incidence were studied. A columnar grain structure is achieved under these conditions with the chromium films having less than theoretical density. The chromium films become denser and less porous as substrate temperatures increases. The lack of full density in the chromium can be ascribed to discontinuities between grains. The iron coatings are denser, exhibiting very large columnar grains, approaching equi-axed, at the higher substrate temperatures. Deposition rates above about 300 Å/s lead to splattering of the evaporant and conelike defects in the films. Vapor deposition at oblique angles leads to less dense coatings, with grain growth occurring radially toward the source. Coatings microstructures were not disturbed by multiple, interrupted deposition. Burnishing or sanding the chromium films tends to densify and crush the coating.