Effect of solid solution tungsten on the radiation-induced amorphization in bulk M23C6 fabricated by vacuum induction melting

To provide a mechanistic understanding of the stability of the M ₂₃C ₆ phase under irradiation, the crystalline to amorphous (c-a) transition behavior in bulk M ₂₃C ₆ specimens with a variation in tungsten (W) content subjected to helium ion irradiation was investigated. The Cr-W-C ternary ingots with a W concentration range of 0–11.6 at.% were fabricated by vacuum-induced furnace melting. Microstructure characterization revealed that the dominant phase in the ingots was M ₂₃C ₆ regardless of the W concentration, and a small amount of metallic-Cr, (Cr, W), and W-rich carbide co-existed as the minor phase. The lattice parameter of M ₂₃C ₆ increases with an increase in W concentration, and the maximum value is 1.083 nm when the W content is 11.6 at.%. Based on this, the chemical formula of the M ₂₃C ₆ particle in F82H steel was represented by Cr ₂₀W ₃C ₆ or Cr ₁₉W ₄C ₆ because its lattice parameter was estimated to be 1.08–1.09 nm. From the grazing incident X-ray diffraction analysis before and after irradiation, the amorphous peak was only observed in the specimen of W concentration 11.6 at.% after irradiation, which was further confirmed by transmission electron microscopy analyses. It is clarified that the c-a transition behavior in M ₂₃C ₆ is dependent on the W content, the amorphization of M ₂₃C ₆ can be mitigated when the W concentration is 6.8 at.% or less under the present study condition.