Difference of the bend-cracks between Ti-coated (011)[100] Si-steel single crystal and ferritic stainless steel

摘要

In order to clarify the crack morphology in 1800 bend-forming of Ti films on a (011)[100] single crystal of silicon steel [sample (a)] and a ferritic stainless steel sheet [sample (b)], Ti coating by the hollow cathode discharge (HCD) method wasperformed on polished steel sheets. The Ti-coated samples were then 1800 bend-formed, and observed using a scanning electron microscope (SEM).Sample (a) showed no distinctive cracks in the Ti films coated on the steel sheet, on which slip lines at interval of 1~5μm in the direction of [1210]{sub}(Ti) could be observed in a rectangular-like morphology 5~25μm in width and 15~60μm in length.Moreover, many fine slip lines at intervals of 50~600 nm in the direction of [0001]{sub}(Ti) could be observed.In contrast, sample (b) exhibited many highly-curved, 10~50μm long cracks in a slightly elongated state.It should be noted that the cracks in the Ti films differed remarkably depending on the kind of steel sheet, that is, whether the steel substrate was a single crystal or polycrystalline. In particular, the Ti films deposited on a (011)[100] single crystal of silicon steel showed epitaxial growth with a good coherency relationship between the Ti film and the silicon steel matrix.