Molecular Dynamics Study of Irradiation-Induced Defect and Dislocation Evolution in Strained Nickel

TL;DR

This study investigates irradiation damage in nickel under coupled mechanical strain by simulating cumulative overlapping $5 keV$ cascades at $300 K$ using MD with a MEAM potential. It tracks defect formation and dislocation evolution via the Dislocation Extraction Algorithm and analyzes heat-spike dynamics under uniaxial strain, enabling a link between irradiation and deformation. Key findings show that tensile strain increases defect survival, reduces heat-spike duration, and drives a Shockley-dominated dislocation landscape with suppressed Hirth dislocations; the defect microstructure saturates at about $rho_ss ≈ 1e15 m^-2$ and is captured by a Kocks-Mecking type balance between accumulation and recovery. Overall, the work provides atomistic insight into radiation–mechanical coupling in nickel, informing design considerations for nuclear materials in extreme environments.

Abstract

Molecular dynamics (MD) simulations were performed to investigate the influence of mechanical strain on irradiation-induced defect and dislocation evolution in nickel single crystals subjected to cumulative overlapping 5 keV collision cascades at 300 K. The simulations reveal that tensile strain modifies the dynamics of defect generation and recovery, promoting stress-assisted defect mobility and enhancing defect survival compared to the unstrained case. The heat spike duration and intensity decrease systematically with increasing strain, indicating faster energy dissipation and altered defect recombination behavior under applied stress. Analysis of the dislocation structure shows that Shockley-type partial dislocations dominate the microstructural response, while Hirth and other dislocation types remain comparatively minor. Both the total and Shockley dislocation densities reach a saturation value of $~10^{16}m^{-2}$ , marking the establishment of a steady-state microstructure governed by the balance between dislocation accumulation and recovery. The evolution of the total dislocation density with strain is successfully described by the Kocks-Mecking model, demonstrating its applicability to strain-dependent irradiation effects in metallic systems

Figures (5)

• Figure 1: Time evolution of defect formation during overlapping 5 keV collision cascades in Ni at 300 K. (a) Unstrained Ni showing the typical rise and decay of defect population associated with the ballistic and recovery phases of individual cascades. (b) Strained Ni illustrating the influence of applied tensile strain, which enhances defect survival and modifies the heat-spike relaxation through stress-assisted defect mobility.
• Figure 2: Heat spike duration and total defect production as a function of applied tensile strain in Ni.
• Figure 3: Evolution of dislocation density for different dislocation types -- total, Shockley, Hirth, Stair-rod, Frank, and Perfect -- during overlapping collision cascades in unstrained Ni at 300 K. The results show that Shockley-type partial dislocations dominate the overall microstructural response, while Frank and Perfect dislocations contribute negligibly.
• Figure 4: Dislocation density evolution as a function of simulation time for strained Ni under overlapping collision cascades. The application of tensile strain promotes the formation of Shockley-type dislocations while reducing the population of Hirth dislocations by approximately one order of magnitude. This behavior arises from stress-assisted defect mobility, which enhances the glide and rearrangement of partial dislocations into more stable Shockley configurations.
• Figure 5: Total dislocation density as a function of applied strain, fitted using the Kocks–Mecking model.