2017 Volume 103 Issue 2 Pages 101-110
Argon ion sputter etching was applied to SUS410 stainless steel at a radio frequency power of 250 W for 1.8 ks to 21.6 ks. When the sputter etching time is 1.8 ks, pillars with diameters smaller than 1 μm are formed perpendicular to the surface of the steel. With increasing sputter etching time, cone-shaped protrusions are formed around the root of the pillars, and the base diameter of the protrusions increases to more than 20 μm at a sputter etching time of 14.4 ks. When the sputter etching time is 21.6 ks, the surface of the protrusions is heavily damaged. An EDX analysis reveals that the Cr content of the pillar is larger than that of the matrix. In addition, an EBSD analysis shows that the protrusions are formed preferentially on the grain surface with {110} plane where the atomic density and sputtering yield are larger than {100} and {111} planes. These facts suggest that the (Cr, Fe)23C6 carbides that are precipitated near the surface of the {110} plane grow more stably as the pillars perpendicular to the plane without being removed by sputtering, i.e. higher temperature, higher temperature gradient and vacancy-density gradient than those of the other planes seem to have promoted the stable growth of pillars by fast diffusion of Cr and C from interior of the grain to the bottom of pillars. The successive diffusion of Cr and C to protrusion surface should be the reason for the stable growth of cone-shaped protrusions even after the sputter shrinkage of the pillars.
