To use chromium thin films to improve the properties of zircalog, some effects of its thickness have been studied. The interface
of Cr/Zr was studied by means of scanning electron microscope (SEM), the composition of the interfaces was identified by an energy dispersive spectrum of X-ray (EDX), the grain morphology of film surfaces were observed by using atomic force microscope (AFM), scratch adhesion tests were performed on a WS-97 Automatic Scratch Tester to examine the adhesion of chromium films to its substrate. The results show that interface of Cr/Zr is well-knit and that there are composition gradient within a narrow region, though there is visible boundary. As the thicknesses of chromium films increase from 0.5μm to 2μm, its grain sizes remain less than microns but grow rapidly, the compact fine-fibre grains become the ones with vaulted top. The scratch tests also demonstrate that the bond strength decreases about 50% between chromium films and their
substrates. When the
thickness of chromium films is up to 1μm, the rates of grain growing and adhesion degrading slow down synchronously, which indicates that the adhesion of chromium films relates with its grain sizes. The adhesion degrades while the film thickness increases, mainly because that the increased thickness changes the film structure and the performance, and increases the film stress.