Defect sink characteristics of specific grain boundary types in 304 stainless steels under high dose neutron environments

Abstract

Radiation induced segregation (RIS) is a well-studied phenomena which occurs in many structurally relevant nuclear materials including austenitic stainless steels. RIS occurs due to solute atoms preferentially coupling with mobile point defect fluxes that migrate and interact with defect sinks. Here, a 304 stainless steel was neutron irradiated up to 47.1 dpa at 320°C. Investigations into the RIS response at specific grain boundary types were utilized to determine the sink characteristics of different boundary types as a function of irradiation dose. A rate theory model built on the foundation of the modified inverse Kirkendall (MIK) model is proposed and benchmarked to the experimental results. This model, termed the GiMIK model, includes alterations in the boundary conditions based on grain boundary structure and expressions for interstitial binding. This investigation, through experiment and modeling, found specific grain boundary structures exhibit unique defect sink characteristics depending on their local structure. Such interactions were found to be consistent across all doses investigated and to have larger global implications, including precipitation of Ni-Si clusters near different grain boundary types.

The role of dislocation channeling in IASCC initiation of neutron irradiated stainless steel

“…However, less irradiation dose achieved this threshold in more aggressive environments, implying that environment interaction with GBs is an important factor (dislocation channeling is independent of corrosion potential). It is possible that changes in GB composition with increasing dose may enhance GB cracking sensitivity, consistent with observations that Σ3 coincident site lattice boundaries are less prone to RIS [53] and IASCC [5] than random high angle (RHA) boundaries.…”

“…GB compositions for the alloys used in this study were analyzed quantitatively using STEM-EDS by Field et al [53,54], showing that RIS increased with irradiation dose in alloy AS. GB Cr depletion has been shown to control IG cracking susceptibility [55], but evidently does not control IASCC because alloy KS (which had no cracking susceptibility) had the lowest GB Cr concentration of the alloys used in this study.…”

“…GB Cr depletion has been shown to control IG cracking susceptibility [55], but evidently does not control IASCC because alloy KS (which had no cracking susceptibility) had the lowest GB Cr concentration of the alloys used in this study. Alternatively, Si segregation increased in alloy AS with dose [53], a factor which enhances IG corrosion in irradiated SS [11,56]. The acidic environment formed within a dissolving MnS crevice was likely analogous to the acidic environment used by Fukuya et al [11] and exacerbated corrosive attack at the GB intersecting this site.…”

Roles of vacancy/interstitial diffusion and segregation in the microchemistry at grain boundaries of irradiated Fe–Cr–Ni alloys

“…Defect production, recombination, and incorporation at sinks such as dislocations and GBs is modeled in the same way as in the Perks [27] and MIK model [21]. Note that the influence of defect sink characteristics such as GB structure is neglected in the following discussion; it is assumed that all sinks act according to perfect sink criteria and hence approximate RIS observed at random high-angle GBs [41]. This approximation was used to simplify the presentation of the model and analysis.…”

Database on Performance of Neutron Irradiated FeCrAl Alloys

“…All grain boundaries were indexed to be random HAGBs. Random HAGBs have been shown through RIS studies to act in the perfect sink criteria [59][60][61][62][63][64] and hence it is anticipated all grain boundaries have the same or very similar defect sink strength and interactions. T irr = 382°C Dose = 1.8 dpa sizes of 40-60 nm.…”