Interface dominated cooperative nanoprecipitation in interstitial alloys

Hongcai Wang,Christoph Somsen,Dingshun Yan,Gunther Eggeler,Xie Zhang

doi:10.1038/s41467-018-06474-w

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 (Fe3C) 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.

Highlights

Steels belong to one of the best established materials, the mechanisms of various phase transformations down to the nano length scale are still not fully clear
Carbide precipitation in steels has been extensively studied in the literature, correlative studies that combine atomic-scale experimental characterizations and theoretical simulations have recently been demonstrated to be an efficient approach for investigating carbide precipitation
It can be seen that the cementite precipitates are a few tens of nanometers long and are confined to be about 5 nanometers wide. These morphological features are indirect evidences for preferred growth directions, even though the precipitation process is not witnessed in situ. This is because the structural transformation from the parent phase to the precipitate may be accomplished by many possible mechanisms, but the driving force is the minimization of the total energy of the system

Summary

Introduction

Steels belong to one of the best established materials, the mechanisms of various phase transformations down to the nano length scale are still not fully clear. We combine high-resolution transmission electron microscopy (HRTEM) with atomistic simulations to unveil the nanoscale growth process of precipitated cementite from the ferrite matrix in a prototypical Fe–Cr–C alloy.

Results

Conclusion