Intergranular Segregation in the Pressure Vessel Steel of a Commercial Nuclear Reactor Studied by Atom Probe Tomography

Abstract

Solute/impurity segregation and precipitation at grain boundaries (GBs) in a nuclear reactor pressure vessel (RPV) steel were investigated using laser-assisted atom probe tomography (APT): RPV surveillance test specimens irradiated in a commercial nuclear reactor to neutron doses of 0.83 © 10 19 n·cm ¹2 (low-dose) and 5.1 © 10 19 n·cm ¹2 (high-dose), corresponding to in-service exposure of ³5 and ³30 years, respectively. The segregation of C, P and Mo was found on GBs after the low-dose irradiation. The segregation of Si and Mn as well as C, P and Mo was observed after the high-dose irradiation. The monolayer coverage of P is estimated to be less than a suggested level for intergranular embrittlement. The segregation of C, P and Mo was also observed along parallel array of dislocation lines in small-angle grain boundaries. However, no segregation of Si and Mn was detected there. Copper-nano precipitates (CNPs) were observed on the GBs, along the dislocation lines and in the matrix. The sizes and the solute-impurity enrichment in these CNPs are compared.

Systematic electronic-structure investigation of substitutional impurity diffusion and flux coupling in bcc iron

“…The effects in irradiated materials are even greater because of the strongly increased concentration of vacancies and self-interstitial atoms (SIA). For instance, the arising of solute drag by vacancies has been shown to be among the main causes for radiationenhanced or -induced solute precipitation [1][2][3], as well as for solute segregation at defect sinks [4][5][6], which in turn are responsible for hardening and embrittlement [7,8]. Solute-defect correlations can also substantially affect defect migration.…”

Molecular Dynamics Simulations of Displacement Cascades in BCC-Fe: Effects of Dislocation, Dislocation Loop and Grain Boundary

“…Before the displacement cascade simulation, the accurate models of edge dislocation, screw dislocation, the dislocation loop and the grain boundary should be introduced, respectively. 1/2 [1][2][3][4][5][6][7][8][9][10][11] edge dislocation with the x slip direction and screw dislocation with the y slip direction were established using Atomsk software (version beta-0.12.1) [25]. The BCC crystal containing dislocation was oriented along the x [112], y and z [−110] directions.…”

“…In nuclear power plants, many structural materials such as A508-III steel and tungsten are exposed to large amounts of neutron irradiation, which could result in irradiation hardening, embrittlement and creep [1][2][3]. For example, irradiation results in increased hardness, yield stress and ductile-brittle transition temperature.…”

“…Moreover, a portion of these defects enter into the dislocation, dislocation loop and grain boundary. During the interaction, 1/2 [1][2][3][4][5][6][7][8][9][10][11] edge dislocation climb occurs while screw dislocation may cross-slip. Compared with edge dislocations, screw dislocations are more likely to absorb point defects.…”

A more holistic characterisation of internal interfaces in a variety of materials via complementary use of transmission Kikuchi diffraction and Atom probe tomography

“…In order to accurately predict changes in the macroscale properties of a material, it is necessary to understand the physical processes that occur during exposure to a particular treatment or environment. Direct measurements of chemical composition of the grain boundary region can assist in understanding the segregation behaviour of elements present in a material system [3][4][5][6] .…”