Deformation Behavior of Surface Layer with Conical and Ring-Shaped Protrusions Formed by Sputter Etching of SUS304 Stainless Steel

Abstract

Austenitic stainless steel (SUS304) specimens were sputter etched by using argon ions, and the formation process of protrusions on the surface was investigated by changing the sputter etching time. In addition, tensile and bending tests of the specimens were carried out to examine whether the delamination between the protrusion and matrix occurs or not. When the sputter etching time is 0.9 ks, fine conical protrusions with diameter smaller than 2 mm are formed relatively homogeneously on the surface. When the sputter etching time is 1.8 ks, they grow to more than 5 mm. In some cases, the holes and cracks are formed on the wall of protrusions. When the sputter etching time is 3.6 ks, the protrusions grow further and occupy whole surface, and finally they collapse to form ring shaped protrusions. The tensile test of the specimens with conical protrusions shows that, even at a fracture strain of 0.53, the shape of the cones is almost maintained and the plastic deformation occurs mainly in the region around them without delamination of the cones. Also in the bending test, the similar behavior to the tensile test is observed. The tensile test of the specimen with ring shaped protrusions also shows that the deformation does not largely occur in the protrusion but occurs in the region outside of them. The reasons for the above characteristics seem to be that the outer shell of the protrusion with higher Cr content is strong and the protrusion grows from interior of specimen keeping high coherency to matrix.

Deformation Characteristics of Fine Protrusions Formed by Sputter-Etching of Stainless Steels

“…The deformation characteristics of conical or ring-shaped protrusions formed on the type 304 stainless steel during tensile and bending tests have been already reported in detail (7) , so only another test result on the same steel sputter-etched for 1.8ks is exhibited here. Fig.…”

“…2(c)), the protrusions have holes and further sputter-etching for more than 5.4ks results in the formation of ring-or wall-shaped protrusions( Fig. 2(d)) (7) . Fig.…”

“…Fig. 3 schematically shows the formation process of conical protrusions with increasing sputter-etching time and damage and decay processes to the ring-shaped protrusions by excess sputtering (7) . Vol.…”

“…7, 2010 Fig. 3 Schematic formation and grow processes of conical protrusions (a, b) , surface damage of protrusion by excess sputtering (c), and decay of the protrusions to form ring-shaped protrusion(d) with increasing sputter-etching time (7) .…”

“…Whatever purpose the surface with protrusions is used, the strength of protrusions is very important. The authors (7) have already reported that the protrusions formed on the type 304 stainless steel never drop out from surface during tensile plastic deformation of the substrate even when fracture of the specimen occurs, which means that the protrusions adhere strongly to the substrate. In addition, the layer with fine protrusions formed on a W-Cr-V tool steel has high resistance to the nano-indentation (9) .…”