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      Interface dominated cooperative nanoprecipitation in interstitial alloys

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          Abstract

          Steels belong to one of the best established materials, however, the mechanisms of various phase transformations down to the nano length scale are still not fully clear. In this work, high-resolution transmission electron microscopy is combined with atomistic simulations to study the nanoscale carbide precipitation in a Fe–Cr–C alloy. We identify a cooperative growth mechanism that connects host lattice reconstruction and interstitial segregation at the growing interface front, which leads to a preferential growth of cementite (Fe 3C) nanoprecipitates along a particular direction. This insight significantly improves our understanding of the mechanisms of nanoscale precipitation in interstitial alloys, and paves the way for engineering nanostructures to enhance the mechanical performance of alloys.

          Abstract

          The specifics of nanoscale precipitation in steels remain complex. Here the authors combine high-resolution microscopy and atomistic simulations to identify a cooperative growth mechanism leading to the preferential growth of cementite nanoprecipitates along a specific crystallographic direction.

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          Generalized Gradient Approximation Made Simple

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            Efficient iterative schemes forab initiototal-energy calculations using a plane-wave basis set

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              Metastable high-entropy dual-phase alloys overcome the strength-ductility trade-off.

              Metals have been mankind's most essential materials for thousands of years; however, their use is affected by ecological and economical concerns. Alloys with higher strength and ductility could alleviate some of these concerns by reducing weight and improving energy efficiency. However, most metallurgical mechanisms for increasing strength lead to ductility loss, an effect referred to as the strength-ductility trade-off. Here we present a metastability-engineering strategy in which we design nanostructured, bulk high-entropy alloys with multiple compositionally equivalent high-entropy phases. High-entropy alloys were originally proposed to benefit from phase stabilization through entropy maximization. Yet here, motivated by recent work that relaxes the strict restrictions on high-entropy alloy compositions by demonstrating the weakness of this connection, the concept is overturned. We decrease phase stability to achieve two key benefits: interface hardening due to a dual-phase microstructure (resulting from reduced thermal stability of the high-temperature phase); and transformation-induced hardening (resulting from the reduced mechanical stability of the room-temperature phase). This combines the best of two worlds: extensive hardening due to the decreased phase stability known from advanced steels and massive solid-solution strengthening of high-entropy alloys. In our transformation-induced plasticity-assisted, dual-phase high-entropy alloy (TRIP-DP-HEA), these two contributions lead respectively to enhanced trans-grain and inter-grain slip resistance, and hence, increased strength. Moreover, the increased strain hardening capacity that is enabled by dislocation hardening of the stable phase and transformation-induced hardening of the metastable phase produces increased ductility. This combined increase in strength and ductility distinguishes the TRIP-DP-HEA alloy from other recently developed structural materials. This metastability-engineering strategy should thus usefully guide design in the near-infinite compositional space of high-entropy alloys.
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                Author and article information

                Contributors
                hongcai.wang@rub.de
                xiezhang@ucsb.edu
                Journal
                Nat Commun
                Nat Commun
                Nature Communications
                Nature Publishing Group UK (London )
                2041-1723
                1 October 2018
                1 October 2018
                2018
                : 9
                : 4017
                Affiliations
                [1 ]ISNI 0000 0004 0490 981X, GRID grid.5570.7, Institut für Werkstoffe, Ruhr-Universität Bochum, ; 44801 Bochum, Germany
                [2 ]ISNI 0000 0004 1936 9676, GRID grid.133342.4, Materials Department, University of California, ; Santa Barbara, CA 93106-5050 USA
                [3 ]GRID grid.458484.1, Institute of Mechanics, Chinese Academy of Sciences, ; Beijing, 100190 China
                Author information
                http://orcid.org/0000-0003-3424-9253
                Article
                6474
                10.1038/s41467-018-06474-w
                6167330
                30275470
                3395a378-8ee3-4cab-a20f-a4e7f892594d
                © The Author(s) 2018

                Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

                History
                : 5 April 2018
                : 7 September 2018
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