Transmission Electron Microscopy Study of the Radiation-Induced Amorphization in the Cr-W-C Ternary M23C6

To provide mechanistic insight into the phase stability of M23C6 under irradiation, bulk M23C6 (Cr-W-C system) specimens with a W concentration range of 0-12 at.% were first subjected to helium ion irradiation and then investigated by systematic TEM/STEM observation. The atomic resolution electron microscopy analysis revealed that the preferential occupation site of the W atom is the 8c site, and the 48h site is also occupied when the W concentration is >7 at.%. The atomic arrangement of the M23C6 particle in F82H steel is similar to that of the specimen of 1W (3 at.% W), and the chemical formula of the M23C6 particle in F82H steel is described as Cr13Fe9W1C6. Radiation-induced amorphization was strongly related to the W concentration in the bulk M23C6, and amorphization was observed only at W concentrations of ∼12 at.% under the present irradiation condition. Line analysis of HAADF and its FFT images confirmed the chemical disordering associated with W atoms, which appears to increase with increasing W concentration. Based on these results, the mechanism of radiation-induced amorphization appears to be different between bulk M23C6 and the M23C6 particles. Specifically, the amorphization of bulk M23C6 is mainly influenced by the addition of a high concentration of W, while the synergistic effects of elements including Cr, Fe, and W are attributed to RIA in fine M23C6 particles. Moreover, the energetic change associated with the W/Fe atom exchange in the M23C6 system is estimated to explain the occurrence of chemical disordering and its resultant amorphization behavior, which provides a new viewpoint to achieve a deeper understanding of the mechanisms behind radiation-induced amorphization. Secondary Abstract The chemical composition of M23C6 particles in F82H steel and the hypothesis of its radiation-induced amorphization mechanism was proposed by HREM observation of He-irradiated M23C6 ingots.