Long-term microstructural evolution of tungsten under heat and neutron loads

Abstract

In nuclear fusion reactors, tungsten will be exposed to high neutron loads at high temperatures (>900°C). The evolution and degradation of the mechanical properties under these conditions is uncertain and therefore constitutes a major risk. Here, the microstructural evolution of tungsten under combined heat and neutron loads is studied, using a multiscale approach incorporating clusters dynamics and a mean-field recrystallization model. The mean-field recrystallization model contains both nucleation in the bulk and at the grain boundaries. The cluster dynamics model includes the incorporation of loops in the dynamics of the dislocation network as a mechanism. The effects of bulk nucleation on the microstructural evolution are explored. The simulations predict a cyclically occuring neutron-induced recrystallization at all studied temperatures. Furthermore, the evolution of the irradiation hardening during neutron-induced recrystallization is assessed from the simulated microstructures. * Correspondence to J. A. W. van Dommelen. Electronic mail: j.a.w.v.dommelen@tue.nl

Controlled irradiation hardening of tungsten by cyclic recrystallization

“…A multi-scale model is used to describe microstructural evolution under neutron loading for a prescribed temperature profile (isothermal or non-isothermal). The framework of the model was described elaborately in [12] and is further extended here. A schematic representation of the model is shown in Figure 1.…”

“…The combined effect of heat and neutron load on the microstructural evolution of tungsten were already studied in [11,12], using multi-scale modelling. In [11], a multi-scale model was presented, consisting of a mean-field recrystallization model and a cluster dynamics model.…”

“…The model was parametrized based on static recrystallization experiments [13] and the evolution of the microstructural properties (grain size distribution, defect distribution) was predicted. Cyclic neutron-induced recrystallization was predicted to occur for temperatures in the range 1000°C -1400°C [12] for the considered microstructure, displacement damage rate and material behaviour. In addition, only a limited irradiation hardening was predicted for cyclic recrystallization [12] at high temperatures.…”

“…Cyclic neutron-induced recrystallization was predicted to occur for temperatures in the range 1000°C -1400°C [12] for the considered microstructure, displacement damage rate and material behaviour. In addition, only a limited irradiation hardening was predicted for cyclic recrystallization [12] at high temperatures. Neutron-induced recrystallization and grain growth were also studied in [14,15].…”

“…In particular, it is studied whether temporary, periodical, extra heating can be used to keep the hardness increase below a certain level. For these non-isothermal studies, the multi-scale model that was presented in [12] is extended, employing a multitude of homogeneous equivalent media (HEMs) instead of just two HEMs, to eliminate the effects of additional parameters in the grain growth part of the model. Furthermore, because of these extensions, a reparametrization of the model is done and it is discussed which recrystallization experiments would be valuable in order to further improve model predictions.…”