Nanomechanical property and microstructural changes of tungsten Langmuir probes retrieved from JET with metal walls

Three tungsten Langmuir probes retrieved from the JET tokamak with the ITER-Like Wall (JET-ILW) from the bulk tungsten Tile 5 have been studied. Nano-indentation, microscopy, ion beam analysis (IBA), and X-ray diffraction were used to assess changes in their mechanical properties, microstructure, and phase composition. Four regions of the probes were studied - the tip and the base, at two sides: front and back. The hardness value of one of the probes (no. 5, Stack B) in the tip area was reduced when compared to the value measured on the base section: 5.4 GPa versus 8.8 GPa, respectively. On the two other probes, the hardness was similar to that of the reference material. At the protrusion of probe 5, the recrystallized zone was observed. The IBA analysis revealed that the probes’ surfaces below the tips were covered by a thin layer of deposit composed primarily of beryllium, oxygen, carbon, and hydrogen isotopes, along with smaller amounts of nickel, nitrogen, and helium at some locations. The presence of tungsten carbide W₂C was revealed on the tip of probe 5, in the area where IBA measurements indicated elevated carbon content in the material, demonstrated by analysis of the XRD records.