An atom probe perspective on phase separation and precipitation in duplex stainless steels

Journal article

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 -Baron-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 hrs, 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 hrs, the number density of 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.

Authors: Haley, D; Garfinkel, D; Tucker, J; Young, G; Poplawsky, J

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Institute of Physics
• Journal: Nanotechnology
• Volume: 27
• Issue: 25
• Article number: 254004
• Publication date: 2016-04-01
• Acceptance date: 2016-04-26
• DOI: 10.1088/0957-4484/27/25/254004
• ISSN: 1361-6528
• Keywords: Fe-Cr alloy; Cu cluster; G-phase; phase separation; atom probe tomography; thermal embrittlement