Competition between recovery and recrystallization in two tungsten supplies according to ITER specifications: Experimental assessment of initial state, recovery kinetics, and grain-boundary mobility, assisted by a mean-field model

In thermonuclear fusion devices, tungsten, implemented as armour material of plasma facing components, is in direct contact with the plasma. Due to high heat flux (20 MW/m 2 ), a premature cracking can be observed in relation with the loss of tungsten mechanical properties. It is usually attributed to two competing restoration processes: recovery and recrystallization. A recent investigation on two tungsten supplies according to ITER specifications has highlighted that hardness abatement at high temperature leads to overestimate the recrystallization fraction, which may be a consequence of the significant contribution of recovery during annealing. The present article aims at investigating this phenomenon through the use of a dedicated mean field recrystallization model that, unlike JMAK models, accounts for physical parameters at the microstructure scale such as recovery parameter or grain boundary mobility. The methodology is applied on the two tungsten supplies for ITER. It allows discriminating, for the first time, the respective contributions of recovery and recrystallization to the macroscopic softening in the high temperature range (from 1450 to 1800 ∘ C ) and annealing times (0–3500 s). The approach has led to the conclusions that the two supplies merely differ from their initial (delivery) state through the stored energy, the initial recrystallized fraction and the grain size but not from intrinsic physical parameters such as recovery parameter or grain boundary mobility.