Investigation of SiC films deposited onto stainless steel and their retarding effects on tritium permeation

Abstract

SiC films were deposited onto thin discs of 316L stainless steel by ion beam assisted deposition (IBAD) and/or ion implantation. The film thickness can be up to 2 μm. The permeability of tritium gas through stainless steel discs was measured at 308∼320°C. The composition and microstructure of the films were also analyzed using X-ray photoelectron spectrometry (XPS), Auger electron spectrometry (AES) X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the modification with SiC films reduces the tritium permeability down to approximately 3×10 −15 mol(NTP) m −1 s −1 MPa −1/2, by five orders of magnitude lower compared with the clean surface of SS 316L. The C/Si atomic ratio in the films depends on the conditions of preparation. A higher C/Si ratio can be obtained with the deposition from both Si and graphite targets and assisted by simultaneous C ion bombardment. A narrow scan XPS of Si 2p and C 1s peaks show that some SiC chemical bonding has formed inside the films. AES line-shapes of C KLL and Si LVV are also indicative of SiC bonding. It has been found by TEM that most IBAD films are amorphous or superfine-grained. However, a number of crystallites can be seen which can be interpreted as α-SiC-2H with the lattice parameter a=0.3076 nm and c=0.5048 nm. The existence of certain Si– and C– dangling bonds is believed to be the origin of tritium trapping and retarded diffusion.