Mechanism of nucleation and incipient growth of Re clusters in irradiated W-Re alloys from kinetic Monte Carlo simulations

Abstract

7High-temperature, high-dose, neutron irradiation of W results in the formation of Re-rich clusters at concentrations one order of magnitude lower than the thermodynamic solubility limit. These clusters may eventually transform into brittle W-Re intermetallic phases, which can lead to high levels of hardening and thermal conductivity losses. Standard theories of radiation enhanced diffusion and precipitation cannot explain the formation of these precipitates and so understanding the mechanism by which nonequilibrium clusters form under irradiation is crucial to predict materials degradation and devise mitigation strategies. Here we carry out a thermodynamic study of W-Re alloys and conduct kinetic Monte Carlo simulations of Re cluster formation in irradiated W2Re alloys using a generalized Hamiltonian for crystals containing point defects parameterized entirely with electronic structure calculations. Our model incorporates recently-gained mechanistic information of mixedinterstitial solute transport, which is seen to control cluster nucleation and growth by forming quasi-spherical nuclei after an average incubation time of 13.5(±8.5) s at 1800 K. These nuclei are seen to grow by attracting more mixed interstitials bringing solute atoms, which in turns attracts vacancies leading to recombination and solute agglomeration. Owing to the arrival of both Re and W atoms from the mixed dumbbells, the clusters are not fully dense in Re, which amounts to no more than 50% of the atomic concentration of the cluster near the center. Our simulations are in qualitative agreement with recent atom probe examinations of ion irradiated W-2Re systems at 773 K.

On the use of ion beams to emulate the neutron irradiation behaviour of tungsten

“…Since the effect of fusion neutrons remains experimentally unavailable there has been a concerted effort to simulate the complex effects of radiation damage and transmutation in the modelling community [75][76][77][78]. Marian et al [76] discussed the need for a multiscale approach when aiming to reproduce the evolution of the many kinds of irradiation defects and transmutation species in W using computer simulation to accurately capture their interaction and synergism.…”

Chemical short-range order in derivative Cr–Ta–Ti–V–W high entropy alloys from the first-principles thermodynamic study

“…For example, some of W-based binary alloys were found to deteriorate the mechanical properties 5,14,21 whereas for other systems such as W-Re, W-Os, transmutation induced precipitations were observed under neutron irradiation. [22][23][24][25] Therefore, the development of new high temperature W-based alloys for plasmafacing materials is paramount to enable fusion as a viable energy source.…”

Kinetic Monte Carlo Simulations of Irradiation Effects

“…In W, transmutation will for instance lead to the formation of Re and Os in non negligible amounts (Gilbert and Sublet 2011). These elements have a strong impact on the mobility of SIAs (Suzudo et al 2015) (Huang et al 2017) and can lead to the formation of brittle intermetallic phases.…”

“…From (Soisson et al 2018) Figure 7: AKMC simulations of α − α′ phase separation in Fe-15%Cr under an irradiation at 290 °C and 3.4 × 10 −7 dpa.s −1 , on the grain boundary and on the neighboring planes. From (Soisson and Jourdan 2016)/ In W, the formation of Re and Os through transmutation has inspired a few KMC (AKMC and OKMC) studies that show that Re and Os impact on the migration of the SIAs (Suzudo et al 2015) (Huang et al 2017). They control the nucleation and the growth of Re-rich clusters and also have a positive impact on swelling and void lattice formation (Bonny et al 2018).…”