Radiation-induced Ostwald ripening in oxide dispersion strengthened ferritic steels irradiated at high ion dose

Abstract

Oxide dispersion strengthened (ODS) ferritic steels are considered promising candidates as cladding tubes for Generation IV nuclear reactors. In such reactors, irradiation damage can reach more than 150 dpa at temperatures ranging from 400 to 650 °C. Thus nanoparticle stability has to be guaranteed in order to ensure that these materials possess excellent creep properties. Using Fe ions, ODS steels were irradiated at 500 °C up to 150 dpa. At this temperature the nano-oxide population evolution under irradiation is similar to that observed after annealing at high temperature. It consists of a slight increase in the particle size and a slight decrease in the density, which can be both explained by an Ostwald ripening mechanism. Conversely, irradiations performed at room temperature using Au ions lead to a complete dissolution of the oxide particles, in agreement with the estimation of ballistic vs. radiation enhanced diffusion effects

The Mechanism of Radiation-Induced Nanocluster Evolution in Oxide Dispersion Strengthened and Ferritic-Martensitic Alloys

“…Heinig, et al [58] developed a method to estimate the average distance a solute atom travels upon ejection ( ̅ ). By executing a SRIM calculation [44] on a thin slab of the cluster composition imbedded in an Fematrix, a recoil distribution is created and an average recoil distance may be determined [59]. Typical values for ̅ are approximately 0.25 -0.35 nm [59], depending on the solute, which is on the same order as the lattice parameter of b.c.c.…”

“…Oxide nanoclusters have been observed to amorphize to varying degrees upon irradiation [59,92,97,101,103,104,108,109,135]. The extent of amorphization is attributed to three factors: 1) the structure of the oxides, 2) irradiation dose, and 3) irradiation temperature [109,135].…”

“…KLSW from Eq. 2.13 is proportional to φ), where φ is the irradiation flux [59,69]. Conversely, other irradiation studies have shown evidence of reduction in average nanocluster size [70] and even of haloing [71,72], in which a high density of smaller nanoclusters nucleate around, and at the expense of, larger nanoclusters.…”

“…Similarly, the data in literature also presents contradictory results with respect to irradiation temperature. Ti ratio has been observed to both increase in some studies [8,9,59,67,88,104,114,116], and decrease in others [81,89,102,116,123,124], while the (T+Ti):O ratio is typically observed to remain the same [8,9,116]. A summary of literature data providing evolution information for these two ratios is provided in Figure 2 Cr enrichment at the interface of nanoclusters [107,112], or depletion of Al from nanoclusters [88,104].…”

“…Since other authors have observed composition changes of nanoclusters under irradiation [8,9,13,59,104,124,174], it is considered likely that the dmax and Nmin values may also differ for each specimen. As a result, both parameters are determined independently for each specimen and each individual data set.…”