Microstructure deformation and near-pore environment of resolidified tungsten in high heat flux conditions

Abstract

Tungsten is a candidate divertor material for many tokamak reactors and has potential to be durable to high heat flux conditions. However, plasma-materials interaction and edge localized modes (1–10 GW/m2) can cause significant hardening and melting damage. Tungsten in a high heat flux (46.3 GW/m2) and helium plasma environment was investigated. We studied possible residual helium and microstructure deformation in resolidified tungsten. Following this, a 1–30 keV Ga focused ion beam was used for TEM sample milling. In as-received tungsten, dark spots of possible lattice strain and defects were in the grains. After high heat exposure under plasma pressure, intergranular features, dark spots in TEM, diffraction patterns, and elongated FIB induced pore-artifact structures (second phase) formed. Helium appears to be absent from the resolidified tungsten matrix due to erosive melting damage and high temperature conditions. A simple four-step microstructure deformation process from the elastic bulk side to the near-pore environment is proposed. The presence of defects in TEM images, grain size reduction, and microstructure deformation affected hardening. The near-pore environment likely experienced grain refinement, and further disordered nanophases are possible under severe deformation conditions.