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Lecture

Recrystallisation in K-doped and pure cold rolled tungsten (W) sheets: As-rolled condition and isochronal annealings (1 h)

Wednesday (26.09.2018)
17:30 - 17:45 S1/01 - A3
Part of:


Cold rolled tungsten with very high degree of deformation and a very fine-grained structure are a very promising structural material for future fusion reactor applications. Main advantages are a high melting point and excellent mechanical properties (e.g. regarding fracture toughness and a sub-zero °C ductile-to-brittle-transition temperature) compared to bulk tungsten materials. However, this very fine-grained structure is not stable at temperatures above 800 °C, which leads to embrittlement through recrystallisation. This study introduces potassium-doping of tungsten sheets to inhibit recrystallisation at high temperatures, a mechanism well known from incandescent lamp wires.


In a first step we produced potassium-doped tungsten sheets by cold rolling with five different degrees of deformation, up to a maximum of φCR = 4.6, as well as pure tungsten sheets with similar degrees of deformation. These sheets are compared structurally by EBSD imaging and microindentation hardness testing.

As a result, both materials reveal similar grain size distributions in normal direction with a substantial grain refinement and increasing hardness values with raising degree of deformation. The K-doped W-sheet reaches the highest hardness values with HV0.1 = 772, compared to the pure W-sheet with HV0.1 = 711. Having similar properties structurally and mechanically, this allows further studies of the new K-doped material to compare the recystallisation behaviour.


In K-doped sheets small pores are distributed between high angular grain boundaries. These “K-bubbles” are known to form strong high temperature barriers. To evaluate the positive effect of the K-bubbles on recrystallisation, first isochronal annealing experiments were carried out. While both materials suffer a sharp drop in hardness values, K-doped W still maintains mediocre values at temperatures above 1400 °C. SEM imaging reveals that large grain growth is suppressed compared to pure W. Therefore, our work will further concentrate on the understanding of the recrystallisation processes in pure and K-doped Tungsten.

 

Speaker:
Philipp Lied
Karlsruhe Institute of Technology (KIT)
Additional Authors:
  • Carsten Bonnekoh
    Karlsruhe Institute of Technology (KIT)
  • Prof. Dr. Wolfgang Pantleon
    Technical University of Denmark (DTU)
  • Dr. Andreas Hoffmann
    PLANSEE SE
  • Dr. Jens Reiser
    Karlsruhe Institute of Technology (KIT)