[en] The probable formation mechanism of He bubble superlattices relies on long range anisotropic diffusion of self-interstitial atoms (SIAs). Here we study He ion irradiation of pure Ni and two equiatomic concentrated solid-solution alloys (CSAs) of FeNi and FeCrNiCo. It is expected from the significantly reduced diffusion of SIAs in CSAs, including high entropy alloys (HEAs), that long range anisotropic SIA migration cannot be active. We report the formation of a He bubble lattice in pure Ni, and for the first time in FeNi and FeCrNiCo systems under 30 keV He ion irradiation at room temperature. The ion dose and flux required to form a bubble superlattice increase with chemical complexity. Comparing to Ni, SIA clusters change directions more frequently due to anisotropic elementally-biased diffusion from the higher degree of chemical non-homogeneity in CSAs. Nevertheless, anisotropic 1-D diffusion of interstitial defects is possible in these complex alloys over incrementally longer time scales and irradiation doses. The sluggish diffusion, characteristic in CSAs, leads to smaller superlattice parameters and smaller bubble diameters. The chemical biased SIA diffusion and its effects on He evolution revealed here have important implications on understanding and improving radiation tolerance over a wide range of extreme conditions.

[en] The computer code, Stopping and Range of Ions in Matter (SRIM), is widely used to describe energetic processes of ion-solid interactions; its predictive power relies on the accuracy of energy loss/transfer and collision processes being considered. While the SRIM code is commonly applied in radiation effects research to predict damage production and in the semiconductor industry to estimate ion range and dopant concentration profiles, two challenges exist that affect its use: (1) inconsistency in estimations of atomic displacements between full-cascade and quick (modified Kinchin–Pease) options and (2) overestimation of electronic stopping power for slow heavy ions in light targets (e.g., Be and Si) or in compound targets containing light elements (e.g., C, N and O in carbides, nitrides and oxides). Based on a literature review and our experimental investigations, we discuss the underlying reasons for the discrepancies, clarify the physical limitations of the SRIM predictions, and, more importantly, provide recommendations to address the two challenges.

[en] We summarize recent advances in modeling of solidification microstructures using computational methods that bridge atomistic to continuum scales. We first discuss progress in atomistic modeling of equilibrium and non-equilibrium solid-liquid interface properties influencing microstructure formation, as well as interface coalescence phenomena influencing the late stages of solidification. The latter is relevant in the context of hot tearing reviewed in the article by M. Rappaz in this issue. We then discuss progress to model microstructures on a continuum scale using phase-field methods. We focus on selected examples in which modeling of 3D cellular and dendritic microstructures has been directly linked to experimental observations. Finally, we discuss a recently introduced coarse-grained dendritic needle network approach to simulate the formation of well-developed dendritic microstructures. The approach reliably bridges the well-separated scales traditionally simulated by phase-field and grain structure models, hence opening new avenues for quantitative modeling of complex intra- and inter-grain dynamical interactions on a grain scale

[en] The effect of energy deposition by energetic particles on Ni and two single-phase concentrated solid solution alloys (NiFe and NiCoCrFe) is explored through combined experimental and modelling efforts. Damage evolution as a function of increasing ion fluence is monitored via elastic strain developed in the irradiated crystals. We show that damage produced from displacement collision cascades is sensitive to subsequent highly ionizing irradiation that the strain generated by elastic nuclear collisions undergoes partial relaxation upon high-energy irradiation. This result suggests a change in the damage structure upon electronic energy deposition due to both predominant defect annealing and growth of small defect clusters. Strain relaxation, more pronounced in the alloys than in Ni, is ascribed to both higher thermal conductivity and weaker electron-phonon coupling in Ni.