Thermal stability of the Cr-coated zirconium alloy microstructure prepared by pulsed laser deposition

Cr-coated zirconium alloy was prepared by pulsed laser deposition(PLD)for the application of accident-tolerant fuel cladding in light water reactors.The microstructural characteristics of the Cr coating and its evolution with temperature were investigated using grazing incidence X-ray diff raction and in situ heating transmission electron microscopy(TEM).Results show that the microstructure of the laser-deposited Cr coatings consists mainly of fine and non-specific shaped nano-crystals in the inner layer and columnar crystals in the outer layer.The recrystallization of the Cr-coating layer starts at 300–400℃ to release the high strain introduced by PLD,and the grain coalescence starts at temperatures>400°C.Upon annealing,the(110)-texture gradually intensifi es because of its high reticular density and low close-packed energy.Additionally,in situ heating TEM observation shows the presence of cavities on the Cr–Zr interface,which may result from the interdiff usion and/or the transformation from amorphous to crystalline.

Effect of niobium content on irradiation microstructure and hardening in FeCrAl-based alloys

Iron-chromium-aluminum(FeCrAl)alloys with different content of niobium(Nb)—0,0.4 wt%,0.8 wt%,and 1.2 wt%—were designed and prepared.All samples were then irradiated with 2.4 MeV Fe^(2+)ion to the dose of 1 and 15 displacements per atom(dpa)at 400℃.The formations of dislocation loops induced by self-ion irradiation in these alloys were investigated by transmission electron microscopy(TEM).Nano-indentation tests were used to assess the hardness and irradiation hardening of samples.For the samples before irradiation,the(Fe,Cr)_(2)(Nb,Mo)Laves phases density and the nano-indentation hardness increased with increasing Nb content of the samples.After irradiation to 1 and 15 dpa,both of a/2<111>and a<100>dislocation loops were produced but no voids orα’phase were found in all samples.With increasing Nb content of the samples,the size of dislocation loops increased first and then decreased,while the total volume number density decreased and then increased.The fraction of a<100>dislocation loops increased first and then decreased with increasing Nb content,and increased with increasing irradiation dose.Dislocation networks and the amorphization of the Laves phases were observed in the samples with irradiation dose of 15 dpa.Irradiation hardening of Nb free samples was two to four times that of Nb containing samples,and the irradiation hardening increased with increasing Nb content of Nb containing samples.The experimental results indicate that the increase of Nb content in Fe Cr Al alloys can increase the density of Laves phases,leading to the decrease of Mo content and increase of Cr content in the matrix.The competition between the two types of solutes affects the nucleation and growth of the dislocation loops.