Mechanism of Radiation Damage Reduction in Equiatomic Multicomponent Single Phase Alloys

Recently a new class of metal alloys, of single-phase multicomponent composition at roughly equal atomic concentrations (“equiatomic”), have been shown to exhibit promising mechanical, magnetic, and corrosion resistance properties, in particular, at high temperatures. These features make them potential candidates for components of next-generation nuclear reactors and other high-radiation environments that will involve high temperatures combined with corrosive environments and extreme radiation exposure. In spite of a wide range of recent studies of many important properties of these alloys, their radiation tolerance at high doses remains unexplored. In this work, a combination of experimental and modeling efforts reveals a substantial reduction of damage accumulation under prolonged irradiation in single-phase NiFe and NiCoCr alloys compared to elemental Ni. This effect is explained by reduced dislocation mobility, which leads to slower growth of large dislocation structures. Moreover, there is no observable phase separation, ordering, or amorphization, pointing to a high phase stability of this class of alloys.

Figure 1

Comparison of irradiation-induced damage in elemental Ni and equiatomic alloys. (a) Rutherford backscattering spectra showing different irradiation response. The higher damage level is observed in the order of Ni, NiFe, and NiCoCr after 1.5 MeV Ni to a fluence of $2\times {10}^{14}{\mathrm{cm}}^{-2}$. (b) Relative disorder in the model systems investigated under 1.5 MeV Ni and 3 MeV Au irradiations. While there exists large uncertainty ($\sim 20\%$) due to the SRIM predictions and channeling analysis, the data clearly show that under these irradiation conditions, much less damage is produced in the NiFe and NiCoCr equiatomic alloys. The dashed lines are curve fits to the data to guide the eye.

Figure 2

Defect cluster distributions in Ni and NiFe at low fluence. (a) High magnification bright-field images of Ni and NiFe samples irradiated using 3 MeV Au ions to a fluence of $2\times {10}^{13}{\mathrm{cm}}^{-2}$ (Peak dose at 155 nm is $\sim 0.1\mathrm{dpa}$) under two beam conditions, $g=[200]$, and (b) size distribution of defect clusters. Interstitial-type dislocation loops are indicated by the dashed circles, and small triangles marked by the dotted circles are characterized as SFT. The scale bar is 20 nm.

Figure 3

Defect cluster distributions in Ni and NiFe at high fluence. Bright-field cross-sectional TEM images ($g=[200]$) showing the overall irradiated region in Ni and NiFe (a) samples after 3 MeV Au ion irradiation to $1\times {10}^{14}{\mathrm{cm}}^{-2}$ (Damage peak at 155 nm is equivalent to 0.57 dpa). (b) Size distribution of defect clusters.

Figure 4

Molecular dynamics results of damage production in Ni, NiFe, and NiCoCr. (a) Buildup of total number of defects and number of defects in clusters larger or equal to 10, divided into point defects and defect clusters. The lines are fits of a function to the data points to guide the eye. The individual data points show fairly large fluctuations since individual dislocation recombination reactions (see text) can cause large changes in the defect numbers. (b) Average cluster size distribution at the dose from $\sim 0.4\mathrm{dpa}$ to the end. The inset shows the same distribution grouped by cluster diameter. (c) Defect structures in Ni and NiFe at a dose of 0.5 dpa. The atoms shown are filtered by removing the perfect structured fcc atoms according to an adaptive common neighbor analysis, to show only atoms that are part of a defective structure.