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    A Nature Research Journal

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    Microstructural Design for Improving Ductility of An Initially Brittle Refractory High Entropy Alloy

    Article | Open | Published:

    , Articlenumber: 8816 ( 2018 ) | Download Citation

    Typically, refractory high-entropy alloys (RHEAs), comprising a two-phase ordered B2 + BCC microstructure, exhibit extraordinarily high yield strengths, but poor ductility at room temperature, limiting their engineering application. The poor ductility is attributed to the continuous matrix being the ordered B2 phase in these alloys. This paper presents a novel approach to microstructural engineering of RHEAs to form an “inverted” BCC + B2 microstructure with discrete B2 precipitates dispersed within a continuous BCC matrix, resulting in improved room temperature compressive ductility, while maintaining high yield strength at both room and elevated temperature.

    Refractory high-entropy alloys (RHEAs) are a relatively new class of multicomponent materials that are based on several refractory metals, but may also contain other, generally low density, elements and typically have a body centered cubic (BCC) crystal structure. These alloys have recently received much attention because of their attractive combination of properties not achievable by other classes of metallic alloys. For example, the first two RHEAs, NbMoTaW and NbMoTaVW, showed weak temperature dependence of yield strength in the temperature range from 600 °C to 1600 °C, with yield strength above 400 MPa at 1600 °C. Unfortunately, these two alloys had high density (>12 g/cm) and further developments aimed at reducing the alloy density while keeping superior high-temperature properties. In the second generation RHEAs, high-density Ta and W were replaced with lower density refractory elements, such as Cr, Mo, Nb, V and Zr, and low density Al and Ti were added. This resulted in RHEAs with lower densities and high-temperature strengths better than the properties of Ni-based superalloys and Fe-based steels. With the exception of the equimolar HfNbTaTiZr and some of its derived compositions most of the reported RHEAs have poor room temperature compressive plasticity, which makes them difficult to process and limits their engineering applications. First-principles calculations showed that alloying intrinsically brittle Mo and W with subgroup IV or V transition metals can make them intrinsically ductile. This composition-induced brittle to ductile transition was explained by changes in the electronic structure, which induced Jahn-Teller distortions and transitioned the elastic instability mode from tensile to shear failure. Extending this theory to RHEAs, Sheikh, . found that single-phase BCC RHEAs consisting of subgroup IV, V and VI metals are intrinsically ductile if the valence electron concentration (VEC) is less than 4.5 and intrinsically brittle if VEC ≥4.6.

    Huang, . and Lilensten, . used a “metastability-engineering” approach, which is similar to well-known transformation-induced plasticity (TRIP), to improve tensile ductility of BCC RHEAs by tailoring the stability of constituent phases. Transformation-induced increase in tensile strain and work-hardening capability were successfully achieved by inducing formation of a stronger HCP phase in a strain-localization region of tensile-tested TaHfZrTi or α” martensite in HfNbTaTiZr. Strain-induced precipitation of the second phase inside the metastable BCC matrix caused strain hardening and slowed strain localization, thus increasing elongation. Similar approaches to enhance uniform tensile ductility resulting from deformation-induced phase transformation were discussed in steels, BCC based titanium alloys, and FCC-based HEAs. Unfortunately, this method is only applicable to intrinsically ductile RHEAs that show low tensile ductility due to rapid strain localization and necking. It cannot be applied to inherently brittle RHEAs that fracture without strain localization/necking and, often, without any macroscopic strain.

    Recently, several Al-containing RHEAs were reported to have a characteristic superalloy-like microstructure, consisting of cuboidal BCC nano-scale precipitates within a coherent B2 matrix, resembling the γ(fcc) + γ’(ordered L1 precipitates) microstructure exhibited by many currently used nickel base superalloys. Although they showed exceptionally good strength at both room and elevated temperatures, substantially exceeding those of single-phase BCC RHEAs, these novel two-phase RHEAs have very limited room temperature compressive ductility, which can be explained by the inherent brittleness of the ordered B2 matrix phase. Unfortunately, the approaches for improving ductility discussed above cannot be applied to this class of Al-containing RHEAs.

    The present work is the first demonstration of enhancing the ductility of high-strength BCC + B2 two-phase RHEAs by controlling their microstructure. For this, AlNbTaTiVZr was selected, based on its low density (7.4 g/cm) and previous reports of excellent room and high temperature yield strength. This alloy was cast, hot isostatically pressed (HIPed) and then homogenized at 1200 °C for 24hrs followed by slow cooling (10 °C/min) to room temperature. The resultant microstructure consists of two BCC phases (one of which is likely ordered, but this was not previously proven) with very similar lattice parameters that form a very fine, inter-woven baskteweave-like, nano-phase structure. Subsequently, this will be referred as Condition (1). The alloy has a room-temperature yield strength of 2035 MPa but only 4.5% compression strain before fracture in Condition (1). The present study focuses on improving the ductility of this alloy by tuning the microstructure, while maintaining its high yield strength.

    The alloy in Condition (1) was solutionized at 1400 °C for 20 min followed by water quenching to achieve a single-phase microstructure. This will be referred to as Condition (2). The alloy in Condition (2) was then annealed at 600 °C for 120 hrs and water-quenched (subsequently referred to as Condition (3)) to possibly develop a two-phase BCC + B2 microstructure.

    Condition (1) was studied here in greater detail using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atom probe tomography (APT). The Condition (1) microstructure is summarized in Fig. Novica Gold accent blue topaz dangle earrings Daisy Queen aym7HMd
    . Annealing at 1200 °C resulted in large, equiaxed grains (grain size = 100 µm ) as seen in the backscattered electron (BSE) SEM image in Fig.. A dark-field TEM image, acquired using a {001} superlattice reflection of the B2 phase, is shown in Fig.. The [001] zone axis electron diffraction pattern is shown as an inset in the same figure. This dark-field TEM image of Condition (1) revealed a highly-refined microstructure consisting of a two-phase mixture. The highlighted brighter regions, forming the continuous matrix, correspond to the ordered B2 phase while the darker discrete pockets correspond to the disordered BCC phase. The edge-to-edge length of the precipitates (disordered BCC) is ~20 nm and the thickness of the channels (ordered B2) is ~2 nm. The precipitates had a very narrow size distribution and were arranged in regular rows along < 001 > direction.

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    Efficacy and Safety of Dupilumab in Glucocorticoid-Dependent Severe Asthma Heat-Stable Carbetocin versus Oxytocin to Prevent Hemorrhage after Vaginal Birth Combined Analysis of Asthma Safety Trials of Long-Acting β2-Agonists What is the diagnosis? Firearm Injuries and Violence Prevention — The Potential Power of a Surgeon Gene... Case 20-2018: A 64-Year-Old Man with Fever, Arthralgias, and Testicular Pain Personhood and the Three Branches of Government Inhaled Corticosteroids and LABAs — Removal of the FDA’s Boxed Warning Progress in Nonmetastatic Prostate Cancer Metastasis-free Survival — A New End Point in Prostate Cancer Trials Adrenal Calcifications in an Infant Accreditation of Clinical Research Sites — Moving Forward Dupilumab Efficacy and Safety in Moderate-to-Severe Uncontrolled Asthma Enzalutamide in Men with Nonmetastatic, Castration-Resistant Prostate Cancer Making Neighborhood-Disadvantage Metrics Accessible — The Neighborhood Atlas New Biologics for Asthma Prophylaxis against Upper Gastrointestinal Bleeding in Hospitalized Patients Tongue Necrosis in Giant-Cell Arteritis


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    N Engl J Med 2014; 371:1084-1086 DOI: 10.1056/NEJMp1409494


    Audio Interview

    Interview with Dr. Anthony Fauci on the current Ebola epidemic and the promise of candidate vaccines and therapies. (11:57) Download

    Ebola Virus Cases and Deaths in West Africa (Guinea, Liberia, Nigeria, and Sierra Leone), as of August 11, 2014 (Panel A), and Over Time (Panel B).

    Data are from the World Health Organization ( ).

    An outbreak of Ebola virus disease (EVD) has jolted West Africa, claiming more than 1000 lives since the virus emerged in Guinea in early 2014 (see figure ). The rapidly increasing numbers of cases in the African countries of Guinea, Liberia, and Sierra Leone have had public health authorities on high alert throughout the spring and summer. More recent events including the spread of EVD to Nigeria (Africa's most populous country) and the recent evacuation to the United States of two American health care workers with EVD have captivated the world's attention and concern. Health professionals and the general public are struggling to comprehend these unfolding dynamics and to separate misinformation and speculation from truth.

    EVD, originally identified in 1976 in Yambuku, Zaire (now the Democratic Republic of Congo), and Nzara, South Sudan, is caused by an RNA virus in the filovirus family. “Ebola” (named after a river in Zaire) encompasses five separate species — and . is not known to cause disease in humans, but the fatality rates in outbreaks of the other four species have ranged from 25 to 90%. The strain currently circulating in West Africa bears 97% homology to samples found in the Democratic Republic of Congo and Gabon. This strain has historically resulted in the highest mortality (90%), although the estimated case fatality rate in the current outbreak is less than 60%.

    Outbreaks probably originate from an animal reservoir and possibly involve additional intermediary species. The most likely reservoir appears to be a fruit bat, although that linkage has not been confirmed. Transmission to humans may have occurred through direct contact with tissue or bodily fluids from an infected animal. Notably, Ebola virus is a zoonotic pathogen, and its circulation among humans is uncommon, which explains the intermittent and unpredictable nature of outbreaks. In fact, although the virus has caused more than 20 outbreaks since its identification in 1976, it had caused fewer than 1600 deaths before 2014, with case counts ranging from a handful to 425 in the Ugandan outbreak of 2000 and 2001. In most instances, the virus emerged in geographically restricted, rural regions, and outbreaks were contained through routine public health measures such as case identification, contact tracing, patient isolation, and quarantine to break the chain of virus transmission.

    In early 2014, EVD emerged in a remote region of Guinea near its borders with Sierra Leone and Liberia. Since then, the epidemic has grown dramatically, fueled by several factors. First, Guinea, Sierra Leone, and Liberia are resource-poor countries already coping with major health challenges, such as malaria and other endemic diseases, some of which may be confused with EVD. Next, their borders are porous, and movement between countries is constant. Health care infrastructure is inadequate, and health workers and essential supplies including personal protective equipment are scarce. Traditional practices, such as bathing of corpses before burial, have facilitated transmission. The epidemic has spread to cities, which complicates tracing of contacts. Finally, decades of conflict have left the populations distrustful of governing officials and authority figures such as health professionals. Add to these problems a rapidly spreading virus with a high mortality rate, and the scope of the challenge becomes clear.

    Although the regional threat of Ebola in West Africa looms large, the chance that the virus will establish a foothold in the United States or another high-resource country remains extremely small. Although global air transit could, and most likely will, allow an infected, asymptomatic person to board a plane and unknowingly carry Ebola virus to a higher-income country, containment should be readily achievable. Hospitals in such countries generally have excellent capacity to isolate persons with suspected cases and to care for them safely should they become ill. Public health authorities have the resources and training necessary to trace and monitor contacts. Protocols exist for the appropriate handling of corpses and disposal of biohazardous materials. In addition, characteristics of the virus itself limit its spread. Numerous studies indicate that direct contact with infected bodily fluids — usually feces, vomit, or blood — is necessary for transmission and that the virus is not transmitted from person to person through the air or by casual contact. Isolation procedures have been clearly outlined by the Centers for Disease Control and Prevention (CDC). A high index of suspicion, proper infection-control practices, and epidemiologic investigations should quickly limit the spread of the virus.

    Frequency of Symptoms Reported in 103 Cases of Ebola Virus Disease in Kikwit, Democratic Republic of Congo, in 1995.

    Recognizing the signs of EVD can be challenging, however, since early symptoms are nonspecific (see box ). It is essential to obtain a careful and prompt travel history. The incubation period typically lasts 5 to 7 days, although it can be as short as 2 days and as long as 21 days. Blood specimens usually begin to test positive on polymerase-chain-reaction–based diagnostics 1 day before symptoms appear. Typical symptoms include fever, profound weakness, and diarrhea. A maculopapular rash has been described, as have laboratory abnormalities including elevated aminotransferase levels, marked lymphocytopenia, and thrombocytopenia. Hemorrhagic complications occur in fewer than half of infected persons, and gross bleeding is relatively rare.

    Once Ebola virus is suspected, the CDC can confirm diagnoses with the use of a diagnostic test approved under an Emergency Use Authorization. Public health measures such as early isolation and infection control are critical. In addition, aggressive supportive care should be administered. Advanced hemodynamic monitoring and interventions that are available in hospitals throughout the United States could result in much higher survival rates than those currently seen in West Africa. With regard to the international transport of patients, the benefits of advanced life-support capabilities that are available in resource-rich countries must be weighed against the risks of air transport, given the hemodynamic instability associated with EVD.

    Recently, substantial attention has been paid to unlicensed therapies and vaccines. Among the therapies in development is a “cocktail” of humanized-mouse antibodies (“ZMapp”), which has shown promise in nonhuman primates. ZMapp was administered to two U.S. citizens who were recently evacuated from Liberia to Atlanta, and both patients have had clinical improvement. However, it is not clear whether ZMapp led to the recovery, and with only two cases, conclusions regarding its efficacy should be withheld. Moreover, the supply of ZMapp remains limited to a handful of doses, and production scale-up, though under way, will take time. Other candidate therapeutics include RNA-polymerase inhibitors and small interfering RNA nanoparticles that inhibit protein production.

    Preclinical evaluation of several vaccine candidates is also under way, and it is anticipated that a candidate developed at the National Institutes of Health will enter a phase 1 trial this fall, pending a decision from the Food and Drug Administration. This vaccine, a chimpanzee adenovirus-vector vaccine, includes two inserted Ebola genes encoding glycoproteins. Two other vaccine candidates involve vesicular stomatitis virus pseudotypes. Human clinical testing of one of these vaccines is expected to begin in early 2015.

    While these interventions remain on accelerated development paths, public health measures are available today that have a proven record of controlling EVD outbreaks. Moreover, premature deployment of unproven interventions could cause inadvertent harm, compromising an already strained relationship between health care professionals and patients in West Africa. Rapid but proper evaluation of candidate therapies and vaccines is needed. Should exemptions be offered for compassionate or emergency use, distribution of scarce interventions must be conducted with careful ethical guidance and regulatory review. It is unlikely that any miracle cure will end the current epidemic. Rather, sound public health practices, engagement with affected communities, and considerable international assistance and global solidarity will be needed to defeat Ebola in West Africa.

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    provided by the author are available with the full text of this article at

    This article was published on August 13, 2014, at

    From the National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD.

    Feldmann H, Geisbert TW. Ebola haemorrhagic fever. ;377:-


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    Beautiful Football

    by Caroline Oatway
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    GRITTY CITY: The Blues showed their character with a hard-fought 2-1 win at Huddersfield

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    knew where he wanted to go: straight out on to the pitch to celebrate what felt like a significant achievement.

    “As Guardiola ushered his players towards the visiting supporters, it seemed the coach simply wanted to be among his men, to congratulate them and make sure they understood how important this victory may prove to be.

    “This was an afternoon when City fell below their sublime best. They were the better team but not wholly themselves. Their intentions were recognisable but their execution was not.

    “When this happens it is important to find a way to win and that City did so may say as much about them as all the pretty goals we have seen previously.

    “Had City faltered here, their lead over Manchester United in the table would have been six points. That would have been healthy enough but with a derby at Old Trafford to come on December 10, there may have been optimism felt across town.

    RS: There are so many pizzerias here, but not many are very good and almost nowhere does it by the slice. My sister’s husband is Italian, and he’s supported me very much, persuading me that it was a good idea. Now we offer more than 150 different kinds of pizzas, but I think what makes us different, and what I keep coming back to is the dough. Our fermentation is for 48 hours in a chamber so that when the dough is cooked it has a thick, chewy crust but at the same time the base is crisp.

    RS: After a year and a half in business I can say we are very happy. The first opened on Sarrià 2-4, next to the Plaça Artós, which is more of a family neighbourhood. After one year we opened our second shop in the centre of Barcelona on Provença 243 between Passeig de Gràcia and Rambla Catalunya where there are lots more tourists, office workers and shops and we’ve found that they all love pizza. At first I think they found it a little strange because they didn’t understand how we worked by weight and they didn’t know how much a slice of pizza would cost, but now I think I can safely say the people love La Fermata!

    RS: Think long and hard about what sort of business you want to open, then search the area where you think you want to be, because it’s all about location, location, location. After that, check out the competition. Some competition is good, too much is not. Finally, and one of the most important things is to see if you have the enough cash flow to open your own business, or if a bank will loan you the cash, with a return of at least five or six years.

    RS: One of my favourites places is Vivanda on Major de Sarrià. Their Mediterranean cooking is amazing, from how they prepare the dishes to the quality of the ingredients. I like Petit Comitè, a Catalan restaurant on Passatge de la Concepció by the popular chef Nando Jubany and my third place is Escribà in Vila Olímpica, right next to the sea and were you can eat the best paella in Barcelona!

    Article published on November 24, 2014 in LF Inspires

    Article tagged with Barcelona , Interviews

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