Metallography of Sputter-Deposited SS304+Al Coatings

Abstract

Plasma-enhanced magnetron sputtered coatings of 304 stainless steel (SS304)+Al containing nominally 0, 4, 7, and 10 wt% Al were deposited on SS304 substrates. The sputter-deposited coatings were characterized for their phase formation and grain size using x-ray diffraction, scanning electron microscopy, and transmission electron microscopy techniques. The sputter-deposited SS304 coatings with no Al contained the metastable phases α and σ, while all other coatings that contained different levels of Al showed the presence of equilibrium phases, namely α-ferrite and B2. The grain size in the coatings varied from nanocrystalline to micron size and showed an increasing trend with an increase in the Al content. Reasons for the formation of the metastable phases and variation of grain size with the Al content in the coatings are discussed. © 2013 Springer Science+Business Media New York and ASM International.