Grain size effect on radiation tolerance of nanocrystalline Mo

Abstract

We report a significant grain size effect on radiation tolerance of nanocrystalline Mo under He ion irradiation. Irradiation-induced dislocation loops mainly contribute to the irradiation-induced hardening of Mo films with grain size of N90 nm, while few such loops in those with grain size of b90 nm. The hardness increment after irradiation decreases with decreasing the grain size, and approaches zero at the grain size of 25 nm. Also, the size and the density of irradiation-induced He bubbles decrease as the grain size decreases. This observation provides direct evidence that nanocrystalline body-centered-cubic metals have greater radiation tolerance than their ultra-fine-grained or coarse-grained counterparts.Published by Elsevier Ltd. Keywords:Radiation damage Body-centered cubic (bcc) Nanocrystalline Grain size effect Magnetron sputtering Radiation damage is one of the critical issues for developing advanced materials used in next generation nuclear plants [1-8] and spacecrafts [9]. Hardening, swelling, embrittlement and creep are some of the critical issues associated with radiation damage. Irradiation can induce interstitials, vacancies or He bubbles in microstructure, which will further agglomerate to form loops, interstitial or vacancy clusters and voids in materials [10,11]. Formation of voids will lead to swelling and embrittlement, which are the main cause of material failure under irradiation environment [12]. Therefore, how to control the generation of irradiation-induced defects and mitigate the negative effects of He bubbles is the key to design advanced radiation tolerant materials with a balance of mechanical and thermal properties [2,13].Body-centered cubic (bcc) metals and alloys have attracted much attention in the past decade due to their reduced-activation under irradiation environment [14][15][16][17][18]. The studies on the oxide-dispersion strengthened (ODS) ferrite steels [19][20][21][22] have showed great radiation tolerance since dispersed nanoparticles in the matrix increase the volume fraction of the interfaces which can act as sinks for irradiation-induced defects, especially for He bubbles.Similarly, nanocrystalline (NC) materials exhibit great potential for such applications because a large fraction of grain and interphase boundaries can act as effective sinks for irradiation-induced vacancies and bubbles [2,6,23,24]. Refining the grains of materials into nanometer size can significantly alter the physical, chemical and mechanical behaviors of the materials [25][26][27][28][29][30][31]. Previous reports [32-35] on fcc/bcc nanolayered composites have showed extreme tolerance to He bubbles, which are prone to segregate at interphase boundaries. Bulk NC metals have also displayed extraordinary radiation healing behavior due to grain boundary (GB) accommodation of defects [36][37][38].Although there are many reports about the radiation damage on NC metals and alloys, it remains elusive about how the change of grain size affects the radiation tolerance. To explore this issue, here we in...

Radiation-Induced Helium Bubbles in Metals

“…In the preceding section, we overview He bubbles nucleation, growth and coarsening in the interior of grains. Interfaces, mainly GBs and heterophase interfaces (bi-metal interfaces), have attracted tremendous interests in the past decades [64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112]. Two reasons are responsible for the tremendous research interest of interfaces.…”

“…Many studies [82,83,84,85] are performed to unveil the dependence of radiation tolerance on grain size and explore the underlying mechanisms on both CG metals and NC metals. Due to their huge disparity in the ratio of GB area to total volume, CG metals and NC metals irradiated by He at the same condition deliver quite different bubble morphologies and distributions [82,83,84,85]. For He irradiation, the enhanced radiation tolerance in NC metals is usually manifested as small and low-density bubbles [82,83,84,85].…”

9R phase enabled superior radiation stability of nanotwinned Cu alloys via in situ radiation at elevated temperature

“…Nanostructured materials contain abundant defect sinks and have shown enhanced radiation tolerance [27,[36][37][38][39]. Grain boundaries (GBs) are one of the effective defect sinks [40], and nanograined (NG) materials show enhanced radiation tolerance compared with their coarse-grained (CG) counterparts as evidenced by fewer defects [41,42], reduced radiation hardening [43], stronger resistance to amorphization [44] and much less void swelling [14,45]. However, due to the high excess energy of conventional high-angle GBs, NG materials often suffer from poor thermal stability [46], and radiation-induced grain coarsening can occur even at room temperature [47].…”

Simulation Study of Helium Effect on the Microstructure of Nanocrystalline Body-Centered Cubic Iron

“…Improved radiation tolerance in nanostructure alloy with a high area fraction of GBhas been reported in many experimental studies. A significant grain size effect on radiation tolerance was observed in nanocrystalline body-centered cubic Mo and Fe under He ion irradiation [11,12]. The density and size of defects (dislocation loops, He bubbles) showed a grain size dependence under irradiation [11,12].…”

“…A significant grain size effect on radiation tolerance was observed in nanocrystalline body-centered cubic Mo and Fe under He ion irradiation [11,12]. The density and size of defects (dislocation loops, He bubbles) showed a grain size dependence under irradiation [11,12]. The He embrittlement might have been reduced due to the high number density of nanoclusters which acted as effective sinks to radiation defects in nanostructured ferritic alloys (NFS) [13,14].…”