Plane and cross-sectional TEM observation to clarify the effect of damage region by ion implantation on induced phase transformation in austenitic 301 stainless steel

Abstract

Phase transformation in austenitic 301 stainless steel was studied under 300 keV Fe+ and Ar+ ions implantations to fluence of 1 × 1021 ions m-2 at room temperature, in order to pursuit the nucleation of martensitic phase transformation in ion-implanted region. Microstructures after ion implantation were observed by transmission electron microscopy (TEM) with plane view and for cross-sectional specimens. The plane view observation of the implanted specimen showed that phase transformation from the γ phase to α phase was induced due to implantation to doses of 5 × 1020 Fe+ ions m-2 and 1 × 1020 Ar+ ions m-2. The nucleation of implantation-induced phase increased with increasing of fluence. The orientation relationship between the γ matrix and the induced α phase was identified to be (11̄0)α ∥ (111̄)γ and [111]α ∥ [011]γ, close to the Kurdjumov-Sachs (K-S) for the Fe+ ion implanted specimen, and (110)α ∥ (111̄)γ and [001]α ∥ [01̄1]γ close to the Nishiyama-Wasserman (N-W) for the Ar+ ion implanted specimen. The cross-sectional observation after implantation revealed that the phase transformation preferentially nucleated in the region near the surface in metal (Fe+) ion implanted specimen, because the gradient of implanted ion concentration attains maximal near the surface. On the other hand, the behavior of phase transformation in the Ar+ ion implanted specimen was different from that of Fe+ ion implantation and the phase was induced at deeper region from surface than Fe+ ion case.