•Machining promoted SCC in annealed 316SS in high temperature water.•SCC initiation was associated with machining marks and did not occur for polished surfaces.•A porous inner oxide layer was a major ...factor affecting SCC initiation on the machined surface.•Machining-induced residual stress did not markedly affect on SCC initiation under SSRT conditions.•Optimized machining parameters that improved productivity and SCC resistance were identified.
The effect of machining on stress corrosion crack initiation of annealed Type 316L stainless steel was investigated through accelerated testing in high-temperature hydrogenated water. It was observed that stress corrosion cracks only initiated on machined surfaces with machining marks perpendicular to the loading direction and a porous inner oxide layer was identified as an important factor contributing to crack initiation. Furthermore, most cracks stopped within the machining-induced near-surface ultrafine-grained layer and the machining-induced residual stresses did not appear to have a significant effect on crack initiation. A correlation between crack initiation and the surface/near-surface features is identified and discussed.
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•Martensite oxidized much faster than austenite in high-temperature hydrogenated water.•The oxide which formed by the consumption of martensite were porous.•The presence of ...strain-induced martensite reduced the SCC initiation susceptibility.
Cold-worked Type 304L/316L stainless steel specimens, which contained different amounts of martensite (α′/ε), were tested in high-temperature hydrogenated water under slow strain rate tensile (SSRT) test conditions to understand the role of martensite on stress corrosion crack (SCC) initiation. These specimens were characterized prior to and after SSRT tests using complementary analytical techniques. It was observed that a higher strain was necessary to induce SCC initiation for cold-rolled 304L that contained martensite compared to the other cold-worked stainless steels that did not contain martensite. The mechanisms responsible for different SCC initiation susceptibilities of the steels were discussed based on the experimental observations.
This paper presents an investigation of the limitations and optimisation of energy dispersive X-ray (EDX) tomography within the scanning transmission electron microscope, focussing on application of ...the technique to characterising the 3D elemental distribution of bimetallic AgAu nanoparticles. The detector collection efficiency when using a standard tomography holder is characterised using a tomographic data set from a single nanoparticle and compared to a standard low background double tilt holder. Optical depth profiling is used to investigate the angles and origin of detector shadowing as a function of specimen field of view. A novel time-varied acquisition scheme is described to compensate for variations in the intensity of spectrum images at each sample tilt. Finally, the ability of EDX spectrum images to satisfy the projection requirement for nanoparticle samples is discussed, with consideration of the effect of absorption and shadowing variations.
•We investigate the methodology of STEM-EDX tomography of nanoparticles.•We present a time-varied acquisition scheme to compensate for detector shadowing.•The ability of STEM-EDX tomography to meet the projection requirement is discussed.
We report the electrochemical detection of the redox active cardiac biomarker myoglobin (Mb) using aptamer-functionalized black phosphorus nanostructured electrodes by measuring direct electron ...transfer. The as-synthesized few-layer black phosphorus nanosheets have been functionalized with poly-l-lysine (PLL) to facilitate binding with generated anti-Mb DNA aptamers on nanostructured electrodes. This aptasensor platform has a record-low detection limit (∼0.524 pg mL–1) and sensitivity (36 μA pg–1 mL cm–2) toward Mb with a dynamic response range from 1 pg mL–1 to 16 μg mL–1 for Mb in serum samples. This strategy opens up avenues to bedside technologies for multiplexed diagnosis of cardiovascular diseases in complex human samples.
Significant elemental segregation is shown to exist within individual hollow silver–gold (Ag–Au) bimetallic nanoparticles obtained from the galvanic reaction between Ag particles and AuCl4 –. ...Three-dimensional compositional mapping using energy dispersive X-ray (EDX) tomography within the scanning transmission electron microscope (STEM) reveals that nanoparticle surface segregation inverts from Au-rich to Ag-rich as Au content increases. Maximum Au surface coverage was observed for nanoparticles with approximately 25 atom % Au, which correlates to the optimal catalytic performance in a three-component coupling reaction among cyclohexane carboxyaldehyde, piperidine, and phenylacetylene.
Recently, the dual beam Xe+ plasma focused ion beam (Xe+pFIB) instrument has attracted increasing interest for site‐specific transmission electron microscopy (TEM) sample preparation for a local ...region of interest as it shows several potential benefits compared to conventional Ga+FIB milling. Nevertheless, challenges and questions remain especially in terms of FIB‐induced artefacts, which hinder reliable S/TEM microstructural and compositional analysis. Here we examine the efficacy of using Xe+ pFIB as compared with conventional Ga+ FIB for TEM sample preparation of Al alloys. Three potential source of specimen preparation artefacts were examined, namely: (1) implantation‐induced defects such as amophisation, dislocations, or ‘bubble’ formation in the near‐surface region resulting from ion bombardment of the sample by the incident beam; (2) compositional artefacts due to implantation of the source ions and (3) material redeposition due to the milling process. It is shown that Xe+pFIB milling is able to produce improved STEM/TEM samples compared to those produced by Ga+ milling, and is therefore the preferred specimen preparation route. Strategies for minimising the artefacts induced by Xe+pFIB and Ga+FIB are also proposed.
Lay Description
FIB (focused ion beam) instruments have become one of the most important systems in the preparation of site‐specific TEM specimens, which are typically 50‐100 nm in thickness. TEM specimen preparation of Al alloys is particularly challenging, as convention Ga‐ion FIB produces artefacts in these materials that make microstructural analysis difficult or impossible. Recently, the use of noble gas ion sources, such as Xe, has markedly improved milling speeds and is being used for the preparation of various materials. Hence, it is necessary to investigate the structural defects formed during FIB milling and assess the ion‐induced chemical contamination in these TEM samples. Here we explore the feasibility and efficiency of using Xe+PFIB as a TEM sample preparation route for Al alloys in comparison with the conventional Ga+FIB.
The capability to perform liquid in situ transmission electron microscopy (TEM) experiments provides an unprecedented opportunity to examine the real-time processes of physical and ...chemical/electrochemical reactions during the interaction between metal surfaces and liquid environments. This work describes the requisite steps to make the technique fully analytical, from sample preparation, through modifications of the electrodes, characterization of electrolytes, and finally to electrochemical corrosion experiments comparing in situ TEM to conventional bulk cell and microcell configurations.
Uranium is typically the most abundant radionuclide by mass in radioactive wastes and is a significant component of effluent streams at nuclear facilities. Actinide(IV) (An(IV)) colloids formed via ...various pathways, including corrosion of spent nuclear fuel, have the potential to greatly enhance the mobility of poorly soluble An(IV) forms, including uranium. This is particularly important in conditions relevant to decommissioning of nuclear facilities and the geological disposal of radioactive waste. Previous studies have suggested that silicate could stabilize U(IV) colloids. Here the formation, composition, and structure of U(IV)-silicate colloids under the alkaline conditions relevant to spent nuclear fuel storage and disposal were investigated using a range of state of the art techniques. The colloids are formed across a range of pH conditions (9–10.5) and silicate concentrations (2–4 mM) and have a primary particle size 1–10 nm, also forming suspended aggregates <220 nm. X-ray absorption spectroscopy, ultrafiltration, and scanning transmission electron microscopy confirm the particles are U(IV)-silicates. Additional evidence from X-ray diffraction and pair distribution function data suggests the primary particles are composed of a UO2-rich core and a U-silicate shell. U(IV)-silicate colloids formation correlates with the formation of U(OH)3(H3SiO4)3 2– complexes in solution indicating they are likely particle precursors. Finally, these colloids form under a range of conditions relevant to nuclear fuel storage and geological disposal of radioactive waste and represent a potential pathway for U mobility in these systems.
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