Wanderka, N.; Isheim, D.; Bakai, A.; Abromeit, C.; Seidman, D.N.: Microstructural stability of a Ni-Mo based Hastelloy after 10 MeV electron irradiation at high temperature. International Journal of Materials Research 101 (2010), p. 631-636
Abstract:
The microstructural changes of a Hastelloy alloy under 10 MeV electron irradiation at 650°C for 700 h to a total dose of 2 x 10-3 dpa (displacements per atom) were investigated by transmission electron microscopy and by 3-dimensional atom-probe tomography utilizing a local-electrode atom-probe tomograph. Transmission electron microscopy analysis before irradiation reveals two types of precipitates: (i) spheroidal with a mean diameter of 22 nm; and (ii) ones with an irregular morphology of a few nm in diameter. The spheroidal precipitates (i) are coherent with the fee matrix and their number density is '" 3 X 1021 m -3. Electron diffraction patterns from these precipitates exhibit superlattice reflections corresponding to the L12 ordered structure. The chemical composition as measured by atomprobe tomography, is about 75 at.% Ni with additions of AI, Ti and Mo. The other type of precipitate (ii) is mainly enriehed in Ni and Mo and its number density is ca.3.6 x 1022 m -3. The diffuse diffraction intensity maxima arising from these precipitates are observed at <l 1/2 O>fcc, which are attributed to compositional short-range order. After electron irradiation, the Ni -AI-rich precipitates (i) exhibiting L h superlattice reflections have disappeared completely, while the diffuse intensity maxima from the Ni -Mo rich clusters (ii) are still visible. The results are discussed with respect to the influence of the electron irradiation on the morphology and structural changes of the ordered precipitates.