Physico-Chemical nanomaterials science

Phase stability of nanostructured materials under irradiation
Shirinyan A.S.1, Bilogorodskyy Y.S.1, Krit O.M.1
1 “Laboratory of composite materials of nuclear-hydrogen energy” of Institute of Applied Physics of National Academy of Sciences of Ukraine. Room 606, building 3, Prospect Nauki, 46, Institute of Physics, Kyiv-03028, Ukraine.
E-mail: aramshirinyan@ukr.net, urabelogorodsky@ukr.net, krit_o_m@ukr.net

Radiation stability of highly dispersed composite materials (NDCM) has been examined intensely in last years but it still remains not complete. A substantial increase of radiation tolerance can be expected in nanocrystalline materials compared to bulk solids with conventional grain sizes, assumed that interfaces NDCM can serve as sinks for vacancies and defects.
We aim to study the effect of vacancy swelling on phase stability of spherical Fe nanoparticle in an inert medium of NDCM. The thermodynamic approach based on the calculation of the Gibbs free energy of Fe nanoparticle for different phase states with vacancy-type defects is offered. Hereby size dependence for the radiation-induced concentrations of point defects is assumed [1]. We investigate radiation tolerance and phase transition bcc-Fe  fcc-Fe depending on the particle size and other parameters [2].
A size dependence of phase transition of Fe nanoparticles on vacancy swelling is found showing the possibility of radiation-induced polymorphic transition, as well as the zone of radiation stability (tolerance) of Fe nanoparticles with respect to the phase transition. Competition between the energy of accumulated vacancies in the particle, the bulk energy of phase transformation and the surface energy of the particle is shown to be responsible for the specific behaviour of irradiated nanocrystalline Fe.

1.	 Shen T.D. Radiation tolerance in a nanostructure: Is smaller better? // Nuclear Instruments and Methods in Physics Research - 2008. - B 266. P. 921–925.
2.	Shirinyan A.S., Bilogorodsky Y.S., Makara V.A. Potential Size-Dependent Temperature Hysteresis of the First-Order Phase Transition in a Nanoscale Metallic Powder // Powder Metallurgy Metal Ceramics - 2017. - 56, P. 253–263.