title: Ultrastrong steel via minimal lattice misfit and high-density nanoprecipitation.
abstract: Next-generation high-performance structural materials are required for lightweight design strategies and advanced energy applications. Maraging steels, combining a martensite matrix with nanoprecipitates, are a class of high-strength materials with the potential for matching these demands. Their outstanding strength originates from semi-coherent precipitates, which unavoidably exhibit a heterogeneous distribution that creates large coherency strains, which in turn may promote crack initiation under load. Here we report a counterintuitive strategy for the design of ultrastrong steel alloys by high-density nanoprecipitation with minimal lattice misfit. We found that these highly dispersed, fully coherent precipitates (that is, the crystal lattice of the precipitates is almost the same as that of the surrounding matrix), showing very low lattice misfit with the matrix and high anti-phase boundary energy, strengthen alloys without sacrificing ductility. Such low lattice misfit (0.03 ± 0.04 per cent) decreases the nucleation barrier for precipitation, thus enabling and stabilizing nanoprecipitates with an extremely high number density (more than 1024per cubic metre) and small size (about 2.7 ± 0.2 nanometres). The minimized elastic misfit strain around the particles does not contribute much to the dislocation interaction, which is typically needed for strength increase. Instead, our strengthening mechanism exploits the chemical ordering effect that creates backstresses (the forces opposing deformation) when precipitates are cut by dislocations. We create a class of steels, strengthened by Ni(Al,Fe) precipitates, with a strength of up to 2.2 gigapascals and good ductility (about 8.2 per cent). The chemical composition of the precipitates enables a substantial reduction in cost compared to conventional maraging steels owing to the replacement of the essential but high-cost alloying elements cobalt and titanium with inexpensive and lightweight aluminium. Strengthening of this class of steel alloy is based on minimal lattice misfit to achieve maximal precipitate dispersion and high cutting stress (the stress required for dislocations to cut through coherent precipitates and thus produce plastic deformation), and we envisage that this lattice misfit design concept may be applied to many other metallic alloys.
authors.affiliation: State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China.
authors.forename: Suihe
authors.initials: S
authors.lastname: Jiang
authors.affiliation: State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Wang
authors.affiliation: State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Wu
authors.affiliation: State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China.
authors.forename: Xiongjun
authors.initials: X
authors.lastname: Liu
authors.affiliation: State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China.
authors.forename: Honghong
authors.initials: H
authors.lastname: Chen
authors.affiliation: Department of Microstructure Physics and Alloy Design, Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Straße, Düsseldorf 40237, Germany.
authors.forename: Mengji
authors.initials: M
authors.lastname: Yao
authors.affiliation: Department of Microstructure Physics and Alloy Design, Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Straße, Düsseldorf 40237, Germany.
authors.forename: Baptiste
authors.initials: B
authors.lastname: Gault
authors.affiliation: Department of Microstructure Physics and Alloy Design, Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Straße, Düsseldorf 40237, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Ponge
authors.affiliation: Department of Microstructure Physics and Alloy Design, Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Straße, Düsseldorf 40237, Germany.
authors.forename: Dierk
authors.initials: D
authors.lastname: Raabe
authors.affiliation: WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.|Mathematics for Advanced Materials-OIL, AIST-Tohoku University, Sendai 980-8577, Japan.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Hirata
authors.affiliation: WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.|Department of Materials Science and Engineering, Johns Hopkins University, Baltimore Maryland 21218, USA.
authors.forename: Mingwei
authors.initials: M
authors.lastname: Chen
authors.affiliation: State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China.
authors.forename: Yandong
authors.initials: Y
authors.lastname: Wang
authors.affiliation: State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China.
authors.forename: Zhaoping
authors.initials: Z
authors.lastname: Lu
mesh_terms: D000535:Aluminum / Q000737:chemistry; D011232:Chemical Precipitation; D003035:Cobalt / Q000737:chemistry; D003722:Dental Alloys / Q000737:chemistry; D004548:Elasticity; D008422:Materials Testing; D017348:Microscopy, Electron, Scanning Transmission; D053758:Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D036103:Nanotechnology; D013232:Steel / Q000737:chemistry* / Q000191:economics; D017356:Synchrotrons; D013718:Tensile Strength; D014025:Titanium / Q000737:chemistry; D014054:Tomography
chemical_list: D003722:Dental Alloys; C093824:Martensite; D013232:Steel; D003035:Cobalt; D000535:Aluminum; D014025:Titanium