Radiation-Induced Segregation and Precipitation in Molybdenum-Rhenium Alloys

Specimens of Mo-7 atomic % Re, Mo-27 atomic % Re, and Mo-30 atomic % Re were irradiated with 1.8-MeV ⁴He⁺ ions at elevated temperatures. Radiation-induced segregation of rhenium was measured during irradiation by in-situ Rutherford backscattering spectrometry (RBS). Segregation of the undersized rhenium atoms in the same direction as the defect fluxes, that is, toward the external surface, was observed. The amount of rhenium enrichment in the near-surface region was measured as a function of temperature and of dose at a calculated near-surface displacement rate near 1 × 10⁻⁴ dpa/s. Segregation was measured by RBS at temperatures from 800 to 1500°C in Mo-7Re, and from 850 to 1225°C in Mo-30Re.

Irradiated disks were examined by transmission electron microscopy. Chi phase precipitation was observed on grain boundaries, and at the irradiated surface in Mo-27Re and Mo-30Re after irradiation at temperatures from 750 to 1075°C. Chi precipitates formed with cube/cube and twin orientations with respect to the host matrix. No voids or loops were observed for ion doses up to 1.6 dpa.