Ultrastrong nanocrystalline steel with exceptional thermal stability and radiation tolerance

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.

Recent progress of radiation response in nanostructured tungsten for nuclear application

“…Various nanocrystalline materials have been developed for radiation resistance [29][30][31]. In coarse-grain material, the diffusion barrier of vacancies is high, and hence the irradiation-induced vacancies migrate slowly and hard to recombine with interstitial atoms.…”

“…Recently, several ultra-uniform nanocrystalline materials were reported via a two-step sintering, which is expected to be used in the tungsten-based nanocrystalline [61,62]. Furthermore, doping elements precipitating around the boundary in the form of oxide nano-clusters could effectively stabilize nano-grain in austenite steel, and this strategy may also encourage the construction of stable tungsten-based nanocrystalline at elevated temperature [31].…”

Limitations of Thermal Stability Analysis via In-Situ TEM/Heating Experiments

“…As a rapid characterization technique to assess thermal stability of NC and UF grained materials, performing in-situ transmission electron microscopy (TEM)/heating experiments has evolved, where thin specimen (preferably below 100 nm) are heated inside the TEM microscope while observing the changes in morphology. These experiments were used on different materials and the thermal stability of these materials in the pristine conditions and irradiated conditions (for nuclear materials) are concluded in some cases based on the in-situ TEM/heating observations [10][11][12][13][14][15].…”

Response of solidification cellular structures in additively manufactured 316 stainless steel to heavy ion irradiation: anin situstudy

“…One major challenge is that the microstructure of metallic materials subjected to high-energy particle irradiation undergoes serious degradation, forming various types of defects, such as Frenkel pairs, dislocation loops, etc., which further undermine the mechanical properties of irradiated materials [12][13][14]. An effective way to mitigate irradiation-induced degradation in materials is to introduce high-density defect sinks [15], such as free surfaces [16], high angle grain boundaries [17,18], twin boundaries [19], and phase interfaces [20]. Recent ex situ proton and helium ion irradiation studies on AM 316 SS found that dense dislocations trapped inside solidification cellular structures tended to undergo recovery and recrystallization during radiation, and may serve as defect sinks, thus help alleviate void swelling and helium bubble formation [9,10].…”