Effect of a nanostructured surface layer on the tensile properties of 316L stainless steel
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Suhua Fan Key Laboratory for Liquid-Solid Structure Evolution and Processing of Materials (Ministry of Education), Shandong University, Jinan 250061, China; and Shandong Women’s University, Jinan 250300, China
Kangning Suna) Key Laboratory for Liquid-Solid Structure Evolution and Processing of Materials (Ministry of Education), Shandong University, Jinan 250061, China; and Engineering Ceramics Key Laboratory of Shandong Province, Shandong University, Jinan 250061, China (Received 15 September 2012; accepted 29 March 2013)
A nanostructured surface layer was fabricated in the surface of 316L stainless steel by a novel fast multiple rotation rolling (FMRR) technique. The microstructure and the tensile properties of the treated sample were investigated in detail. The experimental results indicate that a nanograined (NG) film was successfully obtained in the surface of the sample. Equiaxed nanograins with the average grain size of about 12 nm are achieved in the surface layer. At the sample time, deformation-induced a-martensite is produced during the FMRR treatment. The volume fraction of martensite is about 20%. The yield strength (0.2% offset) of the sample, of which one side is of NG structure and the other is coarse grained (CG), is increased by 51% in comparison with that of the CG sample. Though the plasticity is diminished slightly for the FMRR specimen, the elongation still reaches a high value of about 38% owing to the contribution of the CG structure.
I. INTRODUCTION
A nanograined (NG) metal usually exhibits a higher tensile strength and a lower tensile ductility in comparison with its coarse-grained (CG) counterpart.1 The enhancement of tensile strength can be attributed to the grain refinement, following the well-known Hall–Petch relationship.2,3 The increased brittleness may be attributed to two reasons. First is the reduced dislocation glide, which is effectively obstructed by the extremely small grains. Second is the lack of grain boundary sliding or diffusional creep to accommodate plastic deformation.1 Nieman et al.4 reported that NG Cu prepared by the inert gas condensation method has an elongation of 8%. Karimpoor et al.5 reported that nanocrystalline Co with a 12 nm average grain size has a tensile strength about 3 times that of CG Co while maintaining a 7% elongation in tension. To expand the applications of nanocrystalline materials, an improved strength without much sacrifice in ductility is desired. Since a nanocrystalline metal is strong and brittle, while its CG counterpart is more ductile and less strong, an ideal design of a metal material is such that one side of the metal is NG and the other side is coarse grained, with the a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2013.85 J. Mater. Res., Vol. 28, No. 10, May 28, 2013
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former providing a good global strength and the latter providing ductility. This design can be realized by either ex situ or in situ methods. The ex situ method invo
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