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).

The effect of interstitial carbon on the mechanical properties and dislocation substructure evolution in Fe40.4Ni11.3Mn34.8Al7.5Cr6 high entropy alloys

“…following the procedures described in [21,22]. A local electrode atom probe (CAMECA LEAP 4000X HR) was used to perform the APT experiments with a 50 pJ laser energy, a repetition rate of 200 kHz, and a specimen temperature of 50 K [23].…”

Quantification of hardening contribution of G-Phase precipitation and spinodal decomposition in aged duplex stainless steel: APT analysis and micro-hardness measurements

“…As DSS steels, both spinodal decomposition and G-phase precipitation occur. Guo et al [12] also proposed a hardening model to evaluate hardening due to G-phase precipitation. Their model is based on the Ashby-Orowan equation [46].…”

The effect of carbon on the microstructures, mechanical properties, and deformation mechanisms of thermo-mechanically treated Fe40.4Ni11.3Mn34.8Al7.5Cr6 high entropy alloys

“…% C-doped HEA was characterized using atom probe tomography (APT). A dual FIB-SEM system (FEI Nova 200) was employed to prepare needle-shaped APT tips from grain boundary regions following procedures described elsewhere [24,25]. A site selective FIB liftout was used to target the grain boundary (GB).…”

“…CoCrFeMnNi HEA when the grain size was decreased from 155 µm to 4.4 µm [5], and Fu et al [6] have produced the highest yield strength (1795 MPa) for a HEA, thus far, in nanocrystalline f.c.c. Co 25 Ni 25 Fe 25 Al 7.5 Cu 17.5 with a grain size of 95 nm.…”