Microporosity in 304 stainless steel films prepared by vapor quenching

Thin films of type 304 stainless steel composition were d.c. planar magnetron sputter deposited onto chilled and elevated temperature metallic and non-metallic substrates within the thickness range from 40 nm to 3.5 ωm. Bright field and dark field transmission electron microscopy and electron diffraction techniques were utilized to investigate the as-deposited thin films. A b.c.c. microcrystalline grain structure was obtained through vapor quenching at substrate temperatures (deposition temperatures) between 77 and 473 K. The use of a defocus contrast technique and stereomicroscopy revealed a high density of intergranular and intragranular microvoids in all the films investigated. Microvoids were not observed in 304 stainless steel films sputter deposited by other investigators under similar conditions. Interconnected void networks did not exist in thicker regions of the film but were present in a “channel” in thinner film regions. Both the microcrystalline grain size and the void structures were influenced by the deposition temperature. In this study an attempt is made to evaluate the 304 stainless steel thin film microstructures in the light of their potential for protective coating uses.