Hardness and Depth‐Dependent Microstructure of Ion‐Irradiated Magnesium Aluminate Spinel

Abstract

Stoichiometric polycrystalline magnesium aluminate spinel has been irradiated at 25° and 650°C with 2.4‐MeV Mg+ ions to a fluence of 1.4 × 1021 ions/m2 (∼35 dpa (displacement per atom) peak damage level). Microindentation hardness measurements and transmission electron microscopy combined with energy dispersive X‐ray spectroscopy measurements were used to characterize the irradiation effects. The room‐temperature hardness of spinel increased by about 5% after irradiation at both temperatures. There was no evidence for amorphization at either irradiation temperatures. Interstitial‐type dislocation loops lying on {110} and {111} planes with Burgers vectors along 〈110〉 were observed at intermediate depths (∼1 μm) along the ion range. The 〈110〉{111} loops are presumably formed from 〈111〉{111} loops as a result of a shear on the anion sublattice. Only about 0.05% of the calculated displacements were visible in the form of loops, which indicates that spinel has a high resistance to aggregate damage accumulation. The peak damage region contained a high density of dislocation tangles. There was no evidence for the formation of voids or vacancy loops. The specimen irradiated at 650°C was denuded of dislocation loops within ∼1 μm of the surface.