Deformation mechanisms in an austenitic single-phase duplex microstructured steel with nanotwinned grains

A novel type of duplex microstructure is generated in a single-phase austenitic steel (AISI 316L; X2CrNiMo19-12), consisting of plastically compliant recrystallized austenitic grains as the matrix containing coarse non-recrystallized grains with a nanotwinned austenitic (nt- gamma ) structure as str...

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Veröffentlicht in:Acta materialia 2014-12, Vol.81, p.487-500
Hauptverfasser: YAN, F. K, TAO, N. R, ARCHIE, F, GUTIERREZ-URRUTIA, I, RAABE, D, LU, K
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Sprache:eng
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Zusammenfassung:A novel type of duplex microstructure is generated in a single-phase austenitic steel (AISI 316L; X2CrNiMo19-12), consisting of plastically compliant recrystallized austenitic grains as the matrix containing coarse non-recrystallized grains with a nanotwinned austenitic (nt- gamma ) structure as strengthening inclusions. This novel type of single-phase yet duplex microstructured steel exhibits an excellent combination of strength and ductility. We study the plastic co-deformation mechanisms between the nanotwinned and the recrystallized grains under tension using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). At tensile strains below 5%, the nt- gamma grains nearly deform homogeneously in conjunction with the surrounding statically recrystallized (SRX) grains without generating notable strain localization near their interfaces. The anisotropic plastic deformation of the nt- gamma grains with predominant shear parallel to the twin boundaries results in a higher dislocation density in the neighboring SRX grains. As the strain exceeds 12%, localized deformation occurs within the nt- gamma grains in the form of shear banding. A strain gradient is developed in the surrounding SRX grains as a function of distance from the nt- gamma /SRX interface. Deformation twinning is observed in the SRX grains near the nt- gamma grains, while away from nt- gamma grains dislocation slip dominates the deformation. The strengthening effect of the strong and ductile nt- gamma grains may offer a novel approach to strengthen austenitic steels and related alloys by generating a nanotwinned/recrystallized duplex microstructure.
ISSN:1359-6454
1873-2453
DOI:10.1016/j.actamat.2014.08.054