Core-shell nanoparticle arrays double the strength of steel

J.-B Seol,C.-G Park,S.-H Na,B Gault,J.-C Han,D Raabe,J.-E Kim

doi:10.1038/srep42547

Abstract

Manipulating structure, defects and composition of a material at the atomic scale for enhancing its physical or mechanical properties is referred to as nanostructuring. Here, by combining advanced microscopy techniques, we unveil how formation of highly regular nano-arrays of nanoparticles doubles the strength of an Fe-based alloy, doped with Ti, Mo, and V, from 500 MPa to 1 GPa, upon prolonged heat treatment. The nanoparticles form at moving heterophase interfaces during cooling from the high-temperature face-centered cubic austenite to the body-centered cubic ferrite phase. We observe MoC and TiC nanoparticles at early precipitation stages as well as core-shell nanoparticles with a Ti-C rich core and a Mo-V rich shell at later precipitation stages. The core-shell structure hampers particle coarsening, enhancing the material’s strength. Designing such highly organized metallic core-shell nanoparticle arrays provides a new pathway for developing a wide range of stable nano-architectured engineering metallic alloys with drastically enhanced properties.

Highlights

Manipulating structure, defects and composition of a material at the atomic scale for enhancing its physical or mechanical properties is referred to as nanostructuring
By using atom probe tomography (APT) and high-resolution transmission electron microscopy (HRTEM), we explore the interface-stabilized core-shell NPs and their strictly regular arrangement
The mechanical properties of all the samples were characterized by means of ultimate tensile strength (UTS) and 0.2% offset yield strength (YS)

Summary

Introduction

Manipulating structure, defects and composition of a material at the atomic scale for enhancing its physical or mechanical properties is referred to as nanostructuring. An alternative approach is to exploit the formation of nanometer-sized precipitates through a simple heat treatment These precipitates act as nanoparticles (NPs) dispersed in a solid metallic matrix and provide effective obstacles for dislocation motion, thereby increasing yield strength, high-temperature strength, and creep resistance of numerous engineering alloys[11,12,13,14]. In body-centered cubic (bcc) alloys, strengthening via dispersion of an ultrahigh number density of NPs can be achieved by adding small quantities (≤2 wt.%) of elements (e.g. Ti, Nb, Mo, Ta, V) that promote their formation When finely dispersed, these NPs leave only narrow spaces for dislocations to move freely, so dislocations must curve around or cut through NPs to sweep the material during deformation. The substantially larger interparticle spacings occurring in random obstacle fields leave more room for dislocations to bow out and shear the material at lower stresses, as compared to regular NP arrays which more efficiently hinder dislocation motion[13,14]

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