Microstructural stability of Co-Re-Cr-Ta-C alloy strengthened by TaC precipitates

It is becoming increasingly clear that new materials that can operate at substantially higher temperatures than Ni-base superalloys are needed for future gas turbines. High melting Co-Re-Cr based alloy strengthened by carbides, particularly the MC type carbide, shows promise [1]. A fine dispersion of globular TaC precipitate is exploited for this purpose. Additionally Cr, which is mainly added to improve oxidation resistance, also stabilizes lamellar M23C6 type Cr carbide. The microstructure of a Co-Re-Cr-Ta-C alloy with the two types of carbides is seen in Fig. 1. Please click Additional Files below to see the full abstract

Temperature-dependent Faraday rotation and magnetization reorientation in cerium-substituted yttrium iron garnet thin films

We report on the temperature dependence of the magnetic and magneto-optical properties in cerium-substituted yttrium iron garnet (Ce: YIG) thin films. Measurements of the Faraday rotation as a function of temperature show that the magnetic easy axis of thin Ce: YIG films reorients from in-plane to out-of-plane on cooling below -100 degrees C. We argue that the temperature-dependence of the magnetostriction and magnetocrystalline anisotropy of Ce: YIG is the dominant factor contributing to the change in easy axis direction, and we describe the changes in the magneto-optical spectra with temperature.National Science Foundation (U.S.) (Award ECCS-1607865)United States. Defense Advanced Research Projects Agency (Award FA8650-16-1-7641

Mechanical Properties of Polyvinyl Alcohol/Collagen Hydrogel

Abstract. The effects of the polyvinyl alcohol (PVA) concentration on mechanical properties of hydrogels based on blends of native or denatured collagen / PVA were examined. Blends of PVA with collagen were obtained by mixing the solutions in different ratios, using glycerol as a plasticizer. The solutions were cast on polystyrene plates and the solvent was allowed to evaporate at room temperature. Uniaxial tensile tests were performed in order to obtain the initial stiffness (up to deformation 0.1), the ultimate tensile stress and the deformation at failure of the material in the water-saturated hydrogel form. It was found that the material was elastic and the addition of PVA helped to enhance both the ultimate tensile stress and stiffness of the films. Samples prepared form denaturated collagen showed the higher ultimate tensile stress and the deformation at failure in comparison with those prepared from native collagen. The results suggest that we could expect successful application of the collagen-PVA biomaterial for tissue engineering

Optical investigations of the quality and optical processes of photonic and plasmonic nanostructures

Optical scatterometry based on spectroscopic ellipsometry and other measurement techniques together with optical simualtions are used to analyze the quality of various nanostructure patterns and to study the optical behavior of selected photonic and plasmonic devices

In-situ neutron diffraction study of thermal phase stability in a gamma-TiAl based alloy doped with Mo and/or C

In-situ heating/cooling neutron diffraction experiments were performed on a γ-TiAl based alloy doped with Mo and/or C. The structural analysis was complemented by differential scanning calorimetry and electron microscopy. Description of high temperature α phase with new model of partially disordered View the MathML sourceα2′-Ti3Al phase instead of a fully disordered α-Ti is proposed. The atomic redistribution in the γ phase is related to a wide α-transus signal on the DSC curves. Sections of temperature phase stability diagrams constructed from diffraction data for heating and cooling are presented.Web of Science54382

Is perioperative point-of-care prothrombin time testing accurate compared to the standard laboratory test?

There is no accepted way of measuring prothrombin time without time loss for patients undergoing major surgery who are at risk of intraoperative dilution and consumption coagulopathy due to bleeding and volume replacement with crystalloids or colloids. Decisions to transfuse fresh frozen plasma and procoagulatory drugs have to rely on clinical judgment in these situations. Point-of-care devices are considerably faster than the standard laboratory methods. In this study we assessed the accuracy of a Point-of-care (PoC) device measuring prothrombin time compared to the standard laboratory method. Patients undergoing major surgery and intensive care unit patients were included. PoC prothrombin time was measured by CoaguChek XS Plus (Roche Diagnostics, Switzerland). PoC and reference tests were performed independently and interpreted under blinded conditions. Using a cut-off prothrombin time of 50%, we calculated diagnostic accuracy measures, plotted a receiver operating characteristic (ROC) curve and tested for equivalence between the two methods. PoC sensitivity and specificity were 95% (95% CI 77%, 100%) and 95% (95% CI 91%, 98%) respectively. The negative likelihood ratio was 0.05 (95% CI 0.01, 0.32). The positive likelihood ratio was 19.57 (95% CI 10.62, 36.06). The area under the ROC curve was 0.988. Equivalence between the two methods was confirmed. CoaguChek XS Plus is a rapid and highly accurate test compared with the reference test. These findings suggest that PoC testing will be useful for monitoring intraoperative prothrombin time when coagulopathy is suspected. It could lead to a more rational use of expensive and limited blood bank resources

Additional Phases at High Boron Content in High-Temperature Co–Re–Cr Alloys

Boron largely increases the ductility of polycrystalline high-temperature Co–Re–Cr alloys. Therefore, the effect of boron addition on the alloy structural characteristics is of large importance for the stability of the alloy at operational temperatures. Along with the Co-solid solution matrix phase transformation from hcp to fcc structure, additional structural effects were observed in situ at very high temperatures (up to 1500 °C) using neutron diffraction (ND) in boron-containing Co–17Re–23Cr alloys. Increasing boron content up to 1000 wt. ppm lowers the temperature at which sublimation of Co and Cr from the matrix occurs. As a result, the composition of the matrix in the surface region is changed leading to the formation of a second and a third matrix hcp phases at high temperatures. The consideration on the lattice parameter dependence on composition was used to identify the new phases appearing at high temperatures. Energy-dispersive spectroscopy and ND results were used to estimate the amount of Co and Cr which sublimated from the surface region of the high-boron sample. In the sense of alloy development, the sublimation of Co and Cr is not critical as the temperature range where it is observed (≥1430 °C) is significantly above the foreseen operation temperature of the alloys (1200 °C)

TaC Precipitation Kinetics During Cooling of Co−Re‐Based Alloys

Cobalt−rhenium (Co−Re) alloys are developed for high-temperature applications at ≈1200 °C and are strengthened by dispersion of nanosized tantalum carbide (TaC) precipitates. Herein, the precipitation behavior during cooling from supersolution depending on the cooling rate and the addition of chromium is presented. The phase composition (matrix phases and TaC) is analyzed from the wide-angle neutron diffraction patterns measured in situ during temperature cycling. The precipitation of nanosized TaC particles is measured by in situ and ex situ neutron and X-ray small-angle scattering. The in situ measurements are used to extract the temperature-dependent volume fraction of the precipitates; the final size distribution after cooling is extracted from the ex situ measurements. A Kampmann−Wagner's numerical (KWN) model is adapted to isochronal cooling processes. The in situ measurements give the unique possibility to calibrate the model parameters, whereas the ex situ measurements are used to assess the model predictions

Creep deformation of Co-Re-Ta-C alloys with varying C content – investigated in-situ by simultaneous synchrotron radiation diffraction

The creep deformation of precipitation hardened Co-Re-Ta-C alloys is investigated during in-situ synchrotron diffraction experiment at 1373 K. At room temperature, the alloys have a structure consisting of ϵϵ-Co (hcp) and metastably retained γγ-Co (fcc) and are strengthened by precipitates of the mono-carbide of Ta, which are finely dispersed in the alloy matrix. The alloy exhibits an allotropic ϵ→γϵ→γ-Co phase transformation when heating to View the MathML source>1173K. A lower C content in the alloy generally promotes this transformation. It is shown that this transformation is strongly influenced by application of compressive load. The transformation ϵ→γϵ→γ-Co at high temperature under load leads to microstructure refinement and subsequently to dissolution of hardening precipitates. This results in a considerable acceleration of the creep rate. Further, the equilibrium ratio of γγ/ϵϵ-Co phase is significantly altered under compressive load. This behavior is attributed to a volume relaxation as the ϵϵ- and γγ-Co phase have different unit cell volumes

Fabrication of dual-functional composite yarns with a nanofibrous envelope using high throughput AC needleless and collectorless electrospinning

Abstract Nanotechnologies allow the production of yarns containing nanofibres for use in composites, membranes and biomedical materials. Composite yarns with a conventional thread core for mechanical strength and a nanofibrous envelope for functionality, e.g. biological, catalytic, have many advantages. Until now, the production of such yarns has been technologically difficult. Here, we show an approach to composite yarn production whereby a plume of nanofibers generated by high throughput AC needleless and collectorless electrospinning is wound around a classic thread. In the resulting yarn, nanofibres can form up to 80% of its weight. Our yarn production speed was 10 m/min; testing showed this can be increased to 60 m/min. After the yarn was embedded into knitwear, scanning electron microscope images revealed an intact nanofibrous envelope of the composite yarn. Our results indicate that this production method could lead to the widespread production and use of composite nanofibrous yarns on an industrial scale