Fracture toughness, fracture morphology, and crack-tip plastic zone of a Zr-based bulk amorphous alloy

The elastic constants, fracture toughness, fracture morphology, and crack-tip plastic zone of a bulk amorphous alloy (bulk metallic glass), with the composition Zr-10Al-5Ti-17.9Cu-14.6Ni (at. pct), were investigated. The room-temperature fracture toughness reached values as high as 69 MPa&mrm. However, it showed considerable scatter, which is, at least in part, due to microcrystalline regions in the castings. Controlled crack propagation could not be obtained in chevron-notched specimens. The fracture-surface morphologies of chevron-notched specimens varied as the crack advanced, and this effect is probably related to differences in the crack propagation rate. Controlled fracture resulting in featureless fracture surfaces was observed during in-situ transmission electron microscope (TEM) fracture experiments. The plastic zone of a fatigue-precracked bulk flexure specimen was examined in situ in an atomic-force microscope (AFM). Shear displacements up to 2 &gmm were found. The AFM observations did not reveal any cracks associated with the shear steps. Sectioning of shear steps using a focused ion beam (FIB) with a diameter of 5 nm also did not reveal any cracks.     

The relationship between posttraumatic stress symptoms and sexual risk: Examining potential mechanisms.

Little is known about behavioral and psychological mechanisms that may explain relationships between posttraumatic stress and sexual risks. As rates of HIV infection among African American women remain significantly higher than for other female subgroups, research on sexual risk among African American women is needed. The present study examines the relationships of posttraumatic stress symptoms as measured by the Posttraumatic Stress Disorder Checklist-Civilian Version with sexual risk behaviors, sexual sensation-seeking, and sexual compulsivity in 30 undergraduate African American women with any reported history of sexual intercourse. Higher posttraumatic stress symptoms were associated with more sexual partners, greater frequency of vaginal sex without a condom, and endorsement of sex while under the influence of a substance. Posttraumatic stress symptoms were negatively correlated with perceived sexual control, but were not significantly correlated with sexual compulsivity or sensation-seeking. Perceived sexual control was negatively associated with frequency of unprotected sex and sex under the influence. The preliminary evidence from this small sample suggests sexual control may mediate the relationship of the posttraumatic stress symptoms with unprotected sex. These results are generally consistent with previous findings suggesting posttraumatic stress is associated with sexual risk. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Void formation and morphology in NiAl

Void formation in stoichiometric NiAl was studied through controlled heat treatments and microstructural characterization through transmission electron microscopy. Voids were observed to form at temperatures as low as 400°C, but were noted to dissolve during annealing at 900°C. Two distinct void shapes, cuboidal and rhombic dodecahedral, were observed, often at the same annealing temperature. At higher temperatures (800°C) extensive dislocation climb, rather than void formation, was noted. The relative incidence of void formation and dislocation climb can be related to the mobility of vacancies at each annealing temperature. The shape of void type is described in terms of their relative surface energy and mode of nucleation.     

Analytical electron microscopy of black carbon and microaggregated mineral matter in Amazonian dark Earth

Black carbon (BC) is one of the most stable forms of soil organic matter. Its surface functional groups and structure have been well characterized by a range of analytical methods. However, little is known about the mechanisms of interactions between the BC particles and the surrounding mineral matter. In this paper a range of microscopy techniques, such as transmission electron microscopy and scanning transmission electron microscopy, were used to investigate the possible reactions of BC particles within microaggregates (<2 mm) found in Amazonian dark Earth. Attention is given to the interactions that occur at the interfacial regions between the organic and inorganic phases. Examination of Amazonian dark Earth showed that the carbon-rich phase detected within the BC particles has a significant calcium concentration and a high density of micropores was found at the BC-mineral interface. These observations provide evidence to support suggested mechanisms of interaction between these phases.     

Improving Intermetallic Ductility and Toughness

Many strongly-ordered intermetallic compounds have excellent physical properties which make them potentially useful for structural applications, but many also exhibit extremely low ductility at room temperature. Several techniques, including alloying, microstructural control through processing and fiber strengthening! toughening, have been used to improve the ductility and toughness of inter-metallics.     

Consolidation of ultrafine-grained Cu powder and nanostructured Cu–(2.5–10) vol%Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite powders by powder compact forging

An as-received ultrafine-grained Cu powder and four nanostructured Cu–(2.5–10) vol%Al₂O₃ composite powders produced by high-energy mechanical milling of mixtures of the Cu powder and an Al₂O₃ nanopowder were consolidated using warm powder compaction followed by open die powder compact forging. The circular discs produced in the experiments achieved full densification. Tensile testing of the specimens cut from the forged discs showed that the Cu-forged disc had a fairly high yield strength of 330 MPa, UTS of 340 MPa and a plastic strain to fracture of 15%, but the Cu–Al₂O₃ composite-forged discs did not show any macroscopic plastic yielding. The fracture strength of the composite-forged discs decreased almost linearly with the increase of the volume fraction of Al₂O₃ nanoparticles. This study shows that a high level of consolidation of the ultrafine-grained Cu powder and the nanostructured Cu–2.5 vol%Al₂O₃ composite powder has been achieved by warm powder compacting at 350 °C and powder compact forging at 500 and 700 °C. However, this is not true for the nanostructured Cu–(5, 7.5 and 10) vol%Al₂O₃ composite powders, possibly due to their higher powder particle hardness at elevated temperatures in the range of 350–800 °C.     

K2Ti2O5@C Microspheres with Enhanced K+ Intercalation Pseudocapacitance Ensuring Fast Potassium Storage and Long‐Term Cycling Stability

Benefiting from the natural abundance and low standard redox potential of potassium, potassium‐ion batteries (PIBs) are regarded as one of the most promising alternatives to lithium‐ion batteries for low‐cost energy storage. However, most PIB electrode materials suffer from sluggish thermodynamic kinetics and dramatic volume expansion during K⁺ (de)intercalation. Herein, it is reported on carbon‐coated K₂Ti₂O₅ microspheres (S‐KTO@C) synthesized through a facile spray drying method. Taking advantage of both the porous microstructure and carbon coating, S‐KTO@C shows excellent rate capability and cycling stability as an anode material for PIBs. Furthermore, the intimate integration of carbon coating through chemical vapor deposition technology significantly enhances the K⁺ intercalation pseudocapacitive behavior. As a proof of concept, a potassium‐ion hybrid capacitor is constructed with the S‐KTO@C (battery‐type anode material) and the activated carbon (capacitor‐type cathode material). The assembled device shows a high energy density, high power density, and excellent capacity retention. This work can pave the way for the development of high‐performance potassium‐based energy storage devices.