Bai Cui

Micromechanistic origin of irradiation-assisted stress corrosion cracking

A multi-scale study of the micromechanics of dislocation–grain boundary interactions in proton and ion-irradiated stainless steels is presented. Interactions of dislocation channels with grain boundaries result in slip transfer, discontinuous slip without or with slip along the grain boundary. The presence of the irradiation damage enhances the importance of the magnitude of the resolved shear stress on the slip system activated by the grain boundary to transfer slip across it. However, the selected slip system is still determined by the minimization of the grain boundary strain energy density condition. These findings have implications for modelling the mechanical properties of irradiated metals as well as in establishing the mechanism for disrupting the grain boundary oxide, which is a necessary prerequisite for irradiation-assisted stress corrosion cracking.

Temperature-dependent ion-beam mixing in amorphous SiOC/crystalline Fe composite

The irradiation stability of amorphous SiOC and crystalline Fe interface was investigated by in-situ Kr ion mixing. Results showed intermixing between Fe and SiOC was most severe for irradiation at 50 K and the intermixing decreases as irradiation temperature increases. These findings suggest two characteristic regimes of ion mixing: one regime is independent of temperature and due to ballistic mixing and the other regime is dependent on temperature and is referred to as radiation-enhanced demixing. The occurrence of the temperature-independent mixing and temperature-dependent demixing regimes indicates that the Fe/SiOC nanocomposite is thermodynamically stable and radiation tolerant at elevated temperatures. IMPACT STATEMENT This report reveals two characteristic ion mixing regimes in Fe/SiOC system: one temperature-independent regime and the other temperature-dependent demixing regime, indicating its thermodynamically stability and radiation tolerance at elevated temperatures. GRAPHICAL ABSTRACT

Ultraviolet laser photolysis of hydrocarbons for nondiamond carbon suppression in chemical vapor deposition of diamond films

In this work, we demonstrate that ultraviolet (UV) laser photolysis of hydrocarbon species alters the flame chemistry such that it promotes the diamond growth rate and film quality. Optical emission spectroscopy and laser-induced fluorescence demonstrate that direct UV laser irradiation of a diamond-forming combustion flame produces a large amount of reactive species that play critical roles in diamond growth, thereby leading to enhanced diamond growth. The diamond growth rate is more than doubled, and diamond quality is improved by 4.2%. Investigation of the diamond nucleation process suggests that the diamond nucleation time is significantly shortened and nondiamond carbon accumulation is greatly suppressed with UV laser irradiation of the combustion flame in a laser-parallel-to-substrate geometry. A narrow amorphous carbon transition zone, averaging 4 nm in thickness, is identified at the film–substrate interface area using transmission electron microscopy, confirming the suppression effect of UV laser irradiation on nondiamond carbon formation. The discovery of the advantages of UV photochemistry in diamond growth is of great significance for vastly improving the synthesis of a broad range of technically important materials.

In-Situ TEM Investigation of Interactions between Irradiation Defects and Crystal Defects in Austenitic Stainless Steels

This paper presents our recent efforts that use in-situ irradiation TEM experiments as a tool to understand the interaction process of irradiation defects with crystal defects in austenitic stainless steels (ASS). Various irradiation defect clusters, such as dislocation loops, stacking fault tetrahedra, and voids, can form during the heavy-ion irradiation of ASS. [1] Once nucleated, they interact with the pre-existing crystal defects in the ASS, such as dislocations, grain boundaries and interfaces. These interactions may result in the annihilation of irradiation defects, and thus are important for designing the microstructure of materials with improved irradiation resistance. However, the fundamental mechanisms that control the interactions between irradiation defects and crystal defects are not well understood, due to the complexity of the interaction process. Time-resolved in-situ TEM experiments have the ability to offer real-time observation of the development of irradiation defects and their interactions with crystal defects. These in-situ TEM studies provide experimental evidences as the input to aid the development of physical models for the predication of the microstructure property relationship of ASS in the nuclear reactor environment.