For high temperature mechanical behavior, especially strength and creep behavior, the corresponding microstructure is of key importance. The respective properties of rolled tungsten sheets can be influenced significantly by K-doping. Within this study, the possibility to influence the microstructure of K-doped tungsten sheets via special annealing treatments is investigated. Moreover, the connection to dopant concentrations and limitations to influence the microstructure are analyzed. The annealing processes were carried out with direct resistive sample heating in ultra high vacuum conditions. The microstructure was investigated by in and ex situ methods and compared to the results for pure tungsten.

The respective microstructure can be influenced significantly by the annealing procedure. Especially the temperature increase rate during primary annealing after rolling is showing strong effects. Isothermal annealing afterwards only has limited effects. This stands in contrast to the behaviour of rolled pure tungsten sheets, where normal grain growth is observed. For pure tungsten the total annealing time and temperature are the most important factors regarding the achieved microstructure. All observed effects in K-doped tungsten can be attributed to the formation of a K-bubble structure during annealing. However, the possibilities to influence the microstructure of K-doped tungsten sheets are limited by the recrystallization behaviour and temperature of the respective material. For the investigated temperature increase rates an exponential connection between the grain size and the recrystallization temperature was observed. This connection can be attributed to the corresponding kinetics of recrystallization of K-doped tungsten sheets. The recrystallization temperature is thereby controlled by the dopant distribution within the rolled sheet, especially the K-bubble size and distribution.