Simulating the vacancy saturation effect on phase changes in irradiated nanoparticles using the steady-state approach in chemical rate theory

DOI: 10.62564/M4-AS2232

Aram Shirinyan¹, Yuriy Bilogorodskyy¹, Oleksiy Krit<sup>2

1</sup>Institute of Applied Physics of National Academy of Sciences of Ukraine
²“Laboratory of composite materials of nuclear-hydrogen energy”, Department of nuclear-physical research, Institute of Applied Physics of National Academy of Sciences of Ukraine


The objective of the research is to propose a thermodynamic approach to describe the effects of vacancy saturation on the phase stability of solid nanoparticles during irradiation and to employ the steady-state approach in chemical rate theory to account for radiation defect concentrations. The research is applicable for polymorphic phase transitions in metals (Mo, V, W, Ti, Tl, Zr) and amorphization in ceramics (SiC, TiC). The study demonstrates, via simulation, the potential for radiation-induced α-phase to β-phase transitions and stable radiation zones in initially crystalline nanoparticles. Two model approximations are considered: one resembling iron-like metals with a polymorphic phase transition (α phase is bcc, β phase is fcc) and another resembling SiC-like ceramics with amorphization (α phase is cubic or hexagonal polytype of SiC, β phase is amorphous SiC). Parameters for irradiation include 1MeV ions with fluences ranging from 10 15 to 2×10 16 ions/cm² per second, and defect generation rates (K V ) of nearly 10 -3 - 10 -4 dpa/s for metals and 10 -12 dpa/s for ceramics, vacancy migration energies of 1-2eV for metals and nearly 4eV for crystalline ceramics. Our model study reveals that very small α-phase (bcc) particles are unstable, and α to β phase transformations can occur independently of irradiation. However, in certain scenarios, nucleation of the β-phase necessitates a significant additional energy change, leading to a low probability of α to β phase transition. For larger particle sizes and lower temperatures, α to β transformation becomes impossible regardless of irradiation. Crystalline ceramic materials generally demonstrate notably higher values for the energy of vacancy migration. This implies that the impact of radiation on phase transitions in ceramics is likely to be more significant. In contrast, nanoscale metals exhibit greater resistance to irradiation and thus may be recommended for nuclear materials.

Keywords
vacancy saturation, irradiated nanoparticles, a thermodynamic approach, chemical rate theory, steady-state approach

Acknowledgments
The work is the part of Research of the Laboratory of Composite Materials for Atomic-Hydrogen Energy at the Institute of Applied Physics of NASU (RC 0122U001445, supervision of Ph.D. Aram Shirinyan).

References
[1] Shirinyan A.S., Bilogorodskyy Y.S., Krit O.M. Phase stability of spherical fe nanoparticles under radiation saturation with vacancies // Nuclear Physics and Atomic Energy. 2022. vol. 5. p. 125–129.