Recrystallisation towards a single texture component in heavily cold rolled tungsten (W) sheets and its impact on micromechanics

In this study, we present the recrystallisation behaviour of heavily cold rolled tungsten sheets and show that the material recrystallises towards a single texture component, i.e. the rotated cube component {001} < 110 >. This result is remarkable as it distinguishes from the classical concept of recrystallisation and is likely to have a strong impact in various fields in science and technology. The thermal stability of as-rolled tungsten sheets featuring a thickness reduction of 98% (i.e. 4.1 in the logarithmic notation) was investigated. Annealings were performed in a vacuum and in the temperature range of 400 degrees C (673 K) to 2000 degrees C (2273 K) for a time period of 6 min up to 500 h. The annealing-induced evolution of the microstructure is displayed by hardness (HV0.1) and electron backscatter diffraction (EBSD) measurements. The results show that after an annealing of 6 min at 800 degrees C (1073 K), the hardness drops from 666 +/- 6.3 to 625 +/- 7.9 HV0.1. The evolution of the hardness is fitted by classical kinetic models for recovery (logarithmic kinetics) and recrystallisation. The apparent activation energy of half of the hardness loss, E-Delta HV/2, was found to be 356 kJ/mol (3.69 eV), which can be associated with the activation energy of grain boundary diffusion in tungsten. Furthermore, the hardness data allows for the distinction between two stages. In stage I, the material rapidly develops an equiaxed grain structure by the break-up and spheroidisation of the high aspect ratio grains. We do not observe the formation of nuclei in the classical sense. Moreover, the recrystallisation processes can be described as grain growth. We suggest the dominant driving force to be the reduction of the internal stored energy. Finally, the transition from stage I to stage II is caused by the onset of abnormal grain growth.