Ultrastrong nanocrystalline steel with exceptional thermal stability and radiation tolerance

Congcong Du,Zhongxia Shang,Jin Li,Baoru Sun,Shenyang Hu,Tingting Yang,Xinghang Zhang,Jianyu Huang,Tongde Shen,Yuan Fang,Gang Sha,Ying Zhang,Yugang Wang,Shengwei Xin,Shenbao Jin

doi:10.1038/s41467-018-07712-x

Abstract

Nanocrystalline (NC) metals are stronger and more radiation-tolerant than their coarse-grained (CG) counterparts, but they often suffer from poor thermal stability as nanograins coarsen significantly when heated to 0.3 to 0.5 of their melting temperature (Tm). Here, we report an NC austenitic stainless steel (NC-SS) containing 1 at% lanthanum with an average grain size of 45 nm and an ultrahigh yield strength of ~2.5 GPa that exhibits exceptional thermal stability up to 1000 °C (0.75 Tm). In-situ irradiation to 40 dpa at 450 °C and ex-situ irradiation to 108 dpa at 600 °C produce neither significant grain growth nor void swelling, in contrast to significant void swelling of CG-SS at similar doses. This thermal stability is due to segregation of elemental lanthanum and (La, O, Si)-rich nanoprecipitates at grain boundaries. Microstructure dependent cluster dynamics show grain boundary sinks effectively reduce steady-state vacancy concentrations to suppress void swelling upon irradiation.

Highlights

Nanocrystalline (NC) metals are stronger and more radiation-tolerant than their coarsegrained (CG) counterparts, but they often suffer from poor thermal stability as nanograins coarsen significantly when heated to 0.3 to 0.5 of their melting temperature (Tm)
As-received CG-SS powder is composed of an austenitic phase (Supplementary Figure 1)
No diffraction peaks of elemental La, within the detection limit of the X-ray diffraction, are observed in the NC austenitic stainless steel (NC-SS) after mechanical alloying (MA), suggesting that elemental La is incorporated into the lattice of SS matrix by MA

Summary

Introduction

Nanocrystalline (NC) metals are stronger and more radiation-tolerant than their coarsegrained (CG) counterparts, but they often suffer from poor thermal stability as nanograins coarsen significantly when heated to 0.3 to 0.5 of their melting temperature (Tm). In-situ irradiation to 40 dpa at 450 °C and ex-situ irradiation to 108 dpa at 600 °C produce neither significant grain growth nor void swelling, in contrast to significant void swelling of CG-SS at similar doses This thermal stability is due to segregation of elemental lanthanum and (La, O, Si)-rich nanoprecipitates at grain boundaries. Ferritic steels are widely used in nuclear reactors due to their excellent void swelling resistance, but their creep resistance is poor due to their body-centered cubic structure. Conventional austenitic CG-SSs exhibit poor void swelling resistance in comparison with ferritic steels[21,22]. Designing austenitic SSs with excellent swelling resistance against intense irradiation is a challenge to the nuclear materials community.

Methods

Results

Conclusion