Radiation Resistance of high-entropy nanostructured (Ti, Hf, Zr, V, Nb)N coatings

Abstract

Abstract-The influence of high-fluence ion irradiation of nanostructured (Ti, Hf, Zr, V, Nb)N coatings is revealed for the first time. The energy of irradiating helium ions is equal to 500 keV, and their fluence falls into the interval 5 × 10 16 -3 × 10 17 ions/cm 2 . The performance of the coatings in a nuclear reactor is simulated by conducting post-irradiation thermal annealing at 773 K for 15 min. The elemental composition, structure, morphology, and strength properties of the (Ti, Hf, Zr, V, Nb)N coatings are studied before and after irradiation. No considerable structural and phase modifications in the coatings are found after irradiation, except for the fact that crystallites in the coatings drastically reduce in size to less than 10 nm. Nor does the atomic composition of the coatings change. It is shown that the microhardness of the coatings depends on the fluence of irradiating ions nonlinearly. It can be argued that the (Ti, Hf, Zr, V, Nb)N coatings are radiationresistant and hence promising for claddings of fuel elements in nuclear reactors. DOI: 10.1134/S1063784215100187INTRODUCTION High-entropy nitride alloys, such as (Ti, Hf, Zr, V, Nb)N compounds, are of great interest owing to their unique properties. It was shown [1][2][3][4][5][6][7] that when the entropy extremely rises, relaxation has no time to proceed and the system remains nonequilibrium. This improves the operating performance of coatings, specifically, their properties such as strength, wear resistance, corrosion resistance, heat resistance, and hightemperature stability [1][2][3][4][5]. High entropy is achieved in a multicomponent single-phase disordered solid solution prepared by vacuum deposition. In this method, a coating is deposited on a substrate at a low temperature as a result of which the coating nucleation and growth rates are high. This feature adds to the entropy of the forming system and favors the formation of an ultra-fine-grained structure of the nanocrystalline film.As is known [8], the state of the system is described in terms of the thermodynamic potential function(1) where G is the internal energy, p is the pressure, V is the volume, T is the temperature, and S is the entropy.The stability of a thermodynamic system is characterized by a minimum of the Helmholtz free energy,

Short communication: ‘Low activation, refractory, high entropy alloys for nuclear applications’

“…HEAs are of interest for nuclear applications due to their claimed 'selfhealing' qualities [20,21]. Experimental irradiation studies using heavy ion irradiation demonstrate that HEAs offer superior radiation resistance compared to conventional alloys, with lower density of dislocation loops and less radiation induced segregation which has been attributed to the severe lattice distortion and sluggish diffusion [22,23,24,25]. More recent work has attributed the irradiation resistance of HEAs to two unique properties; firstly a lower phonon mean free path, limiting the cascade induced heat wave propagation, creating a more localised and longer thermal spike which would favor athermal point defect recombination [26] and secondly, a broadening of the interstitial and vacancy migration energy distributions, with possible overlap of the two distributions, which would favor thermal point defect recombination [27].…”

Effects of Nitrogen Selective Sputtering and Flaking of Nanostructured Coating TiN, TiAlN, TiAlYN, TiCrN, (TiHfZrVNb)N under Helium Ion Irradiation

“…The thickness of the localized layer of implanted helium in the TiAlN, TiAlYN, TiCrN coatings increases with the increase in straggling from 325 nm to 375 nm. As mentioned above, this helps to reduce the level of tensile stresses per unit volume of material at high irradiation fluences [8,9,13] and consequently, increase the radiation resistance of coatings. In the coating (TiHfZrVNb)N, the calculated maximum concentration of interstitial helium is minimal among the studied coatings and amounts to: 3.9 at.% at a fluence of 5×10 16 ion/cm 2 , 7.8 at.% at a fluence of 1×10 17 ion/cm 2 , 15.5 at.% at a fluence of 2×10 17 ion/cm 2 , 23 at.% at a fluence of 3 × 10 17 ion/cm 2 .…”

Nanostructured multielement (TiHfZrNbVTa)N coatings before and after implantation of N+ ions (1018cm−2): Their structure and mechanical properties

“…Most of HEA nitrides consist of 5, 6 or 7 elements, but they can incorporate up to 19 elements [38][39][40][41][42][43][44][45] resistance remains still largely unexplored. For the last few years several papers, devoted to the influence of Cu -, Au -, N + ion implantation on hardness, plasticity index and corrosion resistance were published [46][47][48][49][50]. Improvement of different characteristics, such as hardness, were found in the case of relatively high doses of implantation (1-2)Á10 17 cm À2 [46,49,[51][52][53].…”

“…For the last few years several papers, devoted to the influence of Cu -, Au -, N + ion implantation on hardness, plasticity index and corrosion resistance were published [46][47][48][49][50]. Improvement of different characteristics, such as hardness, were found in the case of relatively high doses of implantation (1-2)Á10 17 cm À2 [46,49,[51][52][53]. Overview of published studies devoted to the characteristics and properties of HEA nitride coatings shows that improvement of physicalmechanical characteristics is usually obtained in a narrow ion dose range [54,46,55].…”