An Attempt to Assess Recovery/Recrystallization Kinetics in Tungsten at High Temperature Using Statistical Nanoindentation Analysis

Abstract

Measurement of recovery and recrystallization kinetics of tungsten at high temperature is a key issue for many applications, such as plasma facing units in the framework of thermonuclear fusion. These kinetics are mostly derived from Vickers hardness and EBSD measurements, which can lead to some inaccuracies due to the competition between recovery and recrystallization mechanisms. A complementary/alternative approach based on statistical grid nanoindentation is proposed in this paper. The basic idea is to assume that the fraction recrystallized can be deduced using the hardness probability density function measured on a fully recrystallized sample. The hardness probability density function of the set of non-recrystallized grains can then be analyzed. The methodology was applied to rolled tungsten samples annealed at high temperature. It was clearly observed that recovery and recrystallization overlapped in terms of softening fraction in the investigated time–temperature range. Activation energy of the static recovery mechanism is in the correct order of magnitude compared to bulk self-diffusion in tungsten. High-throughput nanoindentation analysis appears as a promising way to investigate recrystallization/recovery mechanisms in metals.

Evolution of microstructure in neutron irradiated cold rolled tungsten and its correlation with hardness

“…where 0 N is the dislocation density in the unirradiated sample, the lifetime of the dislocations with E the activation energy and B k the Boltzmann constant [51]. In Fig.…”

Thermal stability of the microstructure in rolled tungsten for fusion reactors

“…Such a slow decrease of macroscopic properties or defect densities does not comply with an exponential decay with constant activation energy [5][6][7] (with occasional erroneous claims of the opposite [8]); the required activation energy rather increases in the course of annealing depending on the amount of recovery (as confirmed abanduntly [5][6][7]9]). Kuhlmann [5] has rationalized the logarithmic time dependence at intermediate times as thermally activated decay of the flow stress of the recovering material…”