title: An atom probe perspective on phase separation and precipitation in duplex stainless steels.
abstract: Three-dimensional chemical imaging of Fe-Cr alloys showing Fe-rich (α)/Cr-rich (α') phase separation is reported using atom probe tomography techniques. The extent of phase separation, i.e., amplitude and wavelength, has been quantitatively assessed using the Langer-Bar-on-Miller, proximity histogram, and autocorrelation function methods for two separate Fe-Cr alloys, designated 2101 and 2205. Although the 2101 alloy possesses a larger wavelength and amplitude after annealing at 427 °C for 100-10 000 h, it exhibits a lower hardness than the 2205 alloy. In addition to this phase separation, ultra-fine Ni-Mn-Si-Cu-rich G-phase precipitates form at the α/α' interfaces in both alloys. For the 2101 alloy, Cu clusters act to form a nucleus, around which a Ni-Mn-Si shell develops during the precipitation process. For the 2205 alloy, the Ni and Cu atoms enrich simultaneously and no core-shell chemical distribution was found. This segregation phenomenon may arise from the exact Ni/Cu ratio inside the ferrite. After annealing for 10 000 h, the number density of the G-phase within the 2205 alloy was found to be roughly one order of magnitude higher than in the 2101 alloy. The G-phase precipitates have an additional deleterious effect on the thermal embrittlement, as evaluated by the Ashby-Orowan equation, which explains the discrepancy between the hardness and the rate of phase separation with respect to annealing time (Gladman T 1999 Mater. Sci. Tech. Ser. 15 30-36).
authors.affiliation: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak ridge, TN, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Guo
authors.forename: David A
authors.initials: DA
authors.lastname: Garfinkel
authors.forename: Julie D
authors.initials: JD
authors.lastname: Tucker
authors.forename: Daniel
authors.initials: D
authors.lastname: Haley
authors.forename: George A
authors.initials: GA
authors.lastname: Young
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Poplawsky