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

Abstract

To provide a mechanistic understanding of the stability of the M23C6 phase under irradiation, the crystalline to amorphous (c-a) transition behavior in bulk M23C6 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 M23C6 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 M23C6 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 M23C6 particle in F82H steel was represented by Cr20W3C6 or Cr19W4C6 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 M23C6 is dependent on the W content, the amorphization of M23C6 can be mitigated when the W concentration is 6.8 at.% or less under the present study condition.