Q2. What are the main requirements of tungsten materials for structural divertor applications?
The main requirements of tungsten materials for structural divertor applications compriseproperties like high thermal conductivity, high temperature strength and stability, high recrystallization temperature, and enough ductility for an operation period of about two years under enormous neutron load.
Q3. How can a low activation vanadium-carbide layer be used for joining?
It was demonstrated that diffusion bonding at only 700 °C can be successfully performed with a minimal alteration of the microstructure of the base materials and strongly reduced formation of vanadium-carbide.
Q4. How much tungsten oxides would be released in a single hour?
The linear oxidation rate of tungsten at 1000 °C is about 1.410-2 mg cm-2 s-1 [43], which in the approximately 1000 m2 DEMO first wall would correspond to a release of half a ton of tungsten oxides per hour.
Q5. What was the common method of machining tungsten armour tiles?
Powder injection moulding (PIM) was investigated as a mass fabrication option for the tungstenarmour tiles which had to be joined to the thimbles.
Q6. How long does the D flux take to the surface?
After the implantation has stopped (region III), the D retention drops and a remnant D flux to the W surface takes place for about 10 min.
Q7. What is the impact of a loss of coolant in a fusion power plant?
The use of tungsten as first wall (FW) armour of a fusion power reactor represents an importantsafety concern in the event of a loss of coolant accident with simultaneous air ingress into the reactor vessel.
Q8. What are the main problems related to the use and properties of tungsten materials?
But even neglecting the irradiation effects (due to the large gaps in the knowledge of properties of these materials), there are still unsolved problems related to the use and properties of tungsten materials.
Q9. Why is the brittleness of the tungsten alloys so severe?
Due to the fabrication route, missing mechanical working and/or an increased impurity level could also be an additional explanation for this severe brittleness.
Q10. What are the main uses of a tungsten divertor?
In helium cooled divertor designs tungsten materials are also considered for structural use (e.g. as pressurized pipes or thimbles).
Q11. What is the reason for the formation of small He clusters in tungsten alloys?
The formation of intermetallic compounds in tungsten alloys is just one of the factors responsible for their increased hardening, the other being the conventional solute hardening that gives rise to the embrittlement of the alloys that occurs even in the limit where the concentration of the alloying elements is small.
Q12. What is the effect of the vacancy formation energy in W-Ta alloys?
It shows that the vacancy formation energy in W-Ta alloys depends sensitively on the lattice site at which a vacancy is formed, whereas in W-V alloys it is almost independent of the location of the vacancy site.
Q13. What was the first technique used for manufacturing the fillers?
In the first case, pure metallic powders were mechanically mixed, compacted, and molten to allow for brazing filler materials with homogeneous compositions.
Q14. What is the recent development in tungsten?
In a recent development, precursor powders are fabricated under certain solution conditions where the particle growth could be controlled to produce uniformly yttrium doped nano-sized tungsten oxides.
Q15. How many atomic parts per million are produced in W?
In W, the production of impurities, such as Re, Ta, and Os, is fairly significant, being of the order of a few thousand to tens of thousands of atomic parts per million (appm) over a typical DEMO-like first-wall 5-year neutron exposure.
Q16. How strong was the shear strength of the W-W joints?
Preliminary results of mechanical characterization of these W-W joints using Ti-Fe fillers gave rise to an average shear strength of 140 ± 8 MPa.
Q17. What is the way to improve the ductility of tungsten?
So far, only rhenium is known to improve the ductility of tungsten by solid solution but its usefor fusion energy applications has been ruled out for various reasons (cost, irradiation embrittlement).
Q18. What is the oxidation rate of the WCr12Ti2.5 alloy?
The oxidation behaviour of the WCr12Ti2.5 alloy is similar to that of the WCr10Si10 material; in this case the oxidation rate is similar to that of thin films of same composition at 600 °C but higher at 800 and 1000 °C [48].
Q19. What are the effects of the surface modification processes of the pure hydrogen loaded materials?
Only grain growing and physical sputtering were identified as the surface modification processes of the pure hydrogen loaded materials (Fig. 17).
Q20. What is the possibility of designing alloys where vacancies form within a desired range of temperature?
The results show the possibility of designing alloys where vacancies form within a desired range of temperature, suggesting the possibility of developing alloys with improved stability under irradiation.
Q21. What is the way to characterize the fracture resistance of tungsten?
the fracture resistance may increase with crack propagation, which implies that it is not always possible to characterize the material‘s toughness with one single value such as plane strain fracture toughness KIC or critical energy release rate GIC.
Q22. What are the main subtopics of the W&WALLOYS programme?
In what follows, the results, conclusions, and outlooks are summarized for each of theW&WALLOYS programme‘s main subtopics, which are (1) fabrication, (2) structural W materials, (3) W armour materials, and (4) materials science and modelling.
Q23. What is the effect of the grain boundary crystallography on the fracture properties of tungsten?
Further investigations into the effect of grain boundary crystallography and chemistry are currently on-going, but it appears that tantalum has no beneficial effects, and may even have detrimental effects, on the fracture properties of tungsten.