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

Area of Science:

• Materials Science
• Metallurgy
• Physical Chemistry

Background:

• Fe-Cr alloys are susceptible to phase separation, impacting mechanical properties.
• Understanding precipitation behavior is crucial for alloy performance and stability.

Purpose of the Study:

• To investigate the three-dimensional chemical imaging of Fe-Cr alloys using atom probe tomography.
• To quantitatively assess phase separation and G-phase precipitation in alloys 2101 and 2205.
• To correlate microstructural evolution with mechanical properties like hardness and thermal embrittlement.

Main Methods:

• Atom probe tomography (APT) for 3D chemical imaging.
• Langer-Baron-Miller, proximity histogram, and autocorrelation function methods for phase separation analysis.
• Ashby-Orowan equation for evaluating the effect of precipitates on hardness.

Main Results:

• Fe-rich (α)/Cr-rich (α') phase separation was observed and quantified in both alloys.
• Alloy 2101 showed larger phase separation amplitude and wavelength but lower hardness than alloy 2205.
• Ultra-fine Ni-Mn-Si-Cu-rich G-phase precipitates formed at α/α' interfaces, with higher density in alloy 2205 after prolonged annealing.
• Distinct G-phase formation mechanisms were observed: core-shell in alloy 2101 and simultaneous enrichment in alloy 2205.
• G-phase precipitates were found to contribute to thermal embrittlement.

Conclusions:

• The study elucidates the complex interplay between phase separation, G-phase precipitation, and mechanical properties in Fe-Cr alloys.
• Alloy 2205 exhibits superior hardness despite similar phase separation due to differences in G-phase precipitation and distribution.
• G-phase precipitation significantly influences thermal embrittlement, explaining observed hardness discrepancies.