Swelling and microstructure of A1N irradiated in a fast reactor

Abstract

Abstract Aluminum nitride (A1N) ceramics were neutron-irradiated in the fast-breeder reactor, JOYO, up to 9.1×10 25 n / m 2 ( E >0.1 MeV ) at about 500°C. The macroscopic length expanded 1.74%, whereas the lattice parameter of the c-axis expanded 2.11% compared with 0.05% that of the a-axis. Microstructural observation revealed the formations of high density interstitial-type dislocation loops in grains and microcracks at grain boundaries. The expansion of the c -axis should be related to the introduction of stacking faults by interstitial loop formation on the basal plane. The change in macroscopic volume calculated from macroscopic length became larger than that in a unit cell volume calculated from the lattice parameter. The discrepancy started at around 1% in volume change, corresponding to a fluence of 8×10 24 −2× 10 25 n / m 2 at irradiation temperatures around 500°C. The bending strength of the specimen in this study reduced significantly, which was caused by the microcrack formation along the grain boundary due to the significant anisotropy of lattice expansion.