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- Ademuyiwa, Adesoji O., et al.
(författare)
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Determinants of morbidity and mortality following emergency abdominal surgery in children in low-income and middle-income countries
- 2016
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Ingår i: BMJ Global Health. - : BMJ Publishing Group Ltd. - 2059-7908. ; 1:4
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Tidskriftsartikel (refereegranskat)abstract
- Background: Child health is a key priority on the global health agenda, yet the provision of essential and emergency surgery in children is patchy in resource-poor regions. This study was aimed to determine the mortality risk for emergency abdominal paediatric surgery in low-income countries globally.Methods: Multicentre, international, prospective, cohort study. Self-selected surgical units performing emergency abdominal surgery submitted prespecified data for consecutive children aged <16 years during a 2-week period between July and December 2014. The United Nation's Human Development Index (HDI) was used to stratify countries. The main outcome measure was 30-day postoperative mortality, analysed by multilevel logistic regression.Results: This study included 1409 patients from 253 centres in 43 countries; 282 children were under 2 years of age. Among them, 265 (18.8%) were from low-HDI, 450 (31.9%) from middle-HDI and 694 (49.3%) from high-HDI countries. The most common operations performed were appendectomy, small bowel resection, pyloromyotomy and correction of intussusception. After adjustment for patient and hospital risk factors, child mortality at 30 days was significantly higher in low-HDI (adjusted OR 7.14 (95% CI 2.52 to 20.23), p<0.001) and middle-HDI (4.42 (1.44 to 13.56), p=0.009) countries compared with high-HDI countries, translating to 40 excess deaths per 1000 procedures performed.Conclusions: Adjusted mortality in children following emergency abdominal surgery may be as high as 7 times greater in low-HDI and middle-HDI countries compared with high-HDI countries. Effective provision of emergency essential surgery should be a key priority for global child health agendas.
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| 5. |
- Moravcik, I., et al.
(författare)
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Effect of heat treatment on microstructure and mechanical properties of spark plasma sintered AlCoCrFeNiTi0.5 high entropy alloy
- 2016
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Ingår i: Materials Letters. - : Elsevier BV. - 1873-4979 .- 0167-577X. ; 174, s. 53-56
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Tidskriftsartikel (refereegranskat)abstract
- The present work is focused on synthesis and heat treatment on non-equiatomic AlCoCrFeNiTi0.5 high entropy alloy (HEA) with a composite structure reinforced by TiC nanoparticles. The initial alloy was prepared by mechanical alloying (MA) in a planetary ball mill, compacted by spark plasma sintering (SPS) and heat treated at different temperatures. Mechano-chemical reactions during the MA process as well as the microstructure and hardness of the SPS-ed compacts prior to and after the heat treatment were investigated. During MA, Cr-based supersaturated solid solution with the BCC structure was formed. After SPS at 1100 °C, the BCC solid solution decomposed into nano-grained microstructure consisting of FCC and ordered BCC solid solutions, σ phase, and in-situ formed TiC nanoparticles. The high hardness of the alloy (762 HV) was retained after the subsequent heat treatment at 1100 °C (603 HV). It was shown that the fabrication of TiC reinforced nanocomposites from elemental powders without the use of expensive nanograined powders can be achieved.
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| 6. |
- Prieto, E., et al.
(författare)
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Design and development of a new high entropy alloy by powder metallurgy
- 2016
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Ingår i: World Powder Metallurgy 2016 Congress and Exhibition, World PM 2016; Hamburg; Germany; 9 October 2016 through 13 October 2016. - 9781899072484
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Konferensbidrag (refereegranskat)abstract
- In this work a new high entropy alloy composition has been designed with the aim of tailoring the microstructure to achieve the required properties in cutting tools. For this purpose, it has been taken into account the characteristics of each of the elements involved, combined with the calculation of its phase diagram by thermodynamics simulations. The new composition has been developed by casting, and also by powder metallurgy. In most of the works found in the literature the powders are obtained by mechanical alloying, however in this work the powders are also obtained by atomization in order to reduce the contamination and to obtain powder particles with a more homogeneous composition. Finally the samples consolidation has been performed by spark plasma sintering.
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| 7. |
- Sheikh, Saad Ahmed, 1987
(författare)
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Alloy Design and Optimization of Mechanical Properties of High-Entropy Alloys
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High-entropy alloys (HEAs) are described as alloys containing multi-principal elements in equal or close to equal atomic percentage. HEAs are considered as potential structural materials for high-temperature applications; where alloy design and optimization of mechanical properties is extremely critical. In this regard, achieving both high strength and high tensile ductility is still a great challenge. Compared to conventional alloys, HEAs have high configurational entropy, which tends to stabilize the solid solution formation, mainly face-centered-cubic (fcc) and/or body-centered-cubic (bcc) solid solutions. Generally, fcc-type HEAs are ductile but soft, while bcc-type HEAs are hard but brittle. One part of this work is to understand the solid solubility in HEAs. The need for single-phase solid solution and controlling the formation of TCP/GCP phases, is addressed through the molecular orbital approach. The output of this approach is the Md parameter, the d-orbital energy level, which can well describe the solubility limit in fcc HEAs comprising of only 3d transition metals. However, Md alone cannot describe the solid solubilities in fcc HEAs, which also contain 4d elements. Alloying of 4d elements with 3d elements will cause a large increase of bond order, Bo, which is the measure of the strength of covalent bonds. The use of two-parameter Md - Bo plot can improve the prediction of solid solubility limit when 4d elements are alloyed, but needs further work. The Md approach for bcc HEAs containing 4d elements is also encouraging, but requires more evidence to support this alloy design approach. The second part of this work is to ductilize HEAs containing group IV (Ti, Zr, Hf), V (V, Nb, Ta) and VI (Cr, Mo, W) refractory elements where inadequate ductility puts a limit on their mechanical performance for structural applications. A strategy is proposed here to design refractory HEAs with yield strength reaching 900 MPa, and importantly with sufficient ductility at room temperature. Ductility is introduced by maintaining the number of total valence electrons low, which can be controlled by adjusting the alloy compositions. These findings will shed light on the design of refractory HEAs with optimal mechanical properties.
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| 8. |
- Sheikh, Saad Ahmed, 1987, et al.
(författare)
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Alloy design for intrinsically ductile refractory high-entropy alloys
- 2016
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 120:16, s. Art no 164902-
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Tidskriftsartikel (refereegranskat)abstract
- Refractory high-entropy alloys (RHEAs), comprising group IV (Ti, Zr, Hf), V (V, Nb, Ta), and VI (Cr, Mo, W) refractory elements, can be potentially new generation high-temperature materials. However, most existing RHEAs lack room-temperature ductility, similar to conventional refractory metals and alloys. Here, we propose an alloy design strategy to intrinsically ductilize RHEAs based on the electron theory and more specifically to decrease the number of valence electrons through controlled alloying. A new ductile RHEA, Hf0.5 Nb 0.5 Ta 0.5Ti1.5Zr, was developed as a proof of concept, with a fracture stress of close to 1 GPa and an elongation of near 20%. The findings here will shed light on the development of ductile RHEAs for ultrahigh-temperature applications in aerospace and power-generation industries.
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| 9. |
- Wani, I. S., et al.
(författare)
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Tailoring nanostructures and mechanical properties of AlCoCrFeNi2.1 eutectic high entropy alloy using thermo-mechanical processing
- 2016
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Ingår i: Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing. - : Elsevier BV. - 0921-5093. ; 675, s. 99-109
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Tidskriftsartikel (refereegranskat)abstract
- The effect of thermo-mechanical processing on the evolution of microstructure and mechanical properties was investigated in an AlCoCrFeNi2.1 high entropy alloy. For this purpose, the alloy was cold-rolled to 90% reduction in thickness and annealed at temperatures ranging from 800 °C to 1200 °C. The as-cast alloy revealed eutectic lamellar mixture of (Ni, Al) rich but Cr depleted B2 phase and Al-depleted L12 phases, having volume fractions of ~35% and 65%, respectively. Nanosized precipitates enriched in Cr and having disordered BCC structure were found dispersed inside the B2 phase. Cold-rolling resulted in progressive disordering of the L12 phase but the B2 phase maintained the ordered structure. The disordering of the L12 phase was accompanied by the evolution of ultrafine lamellar structure and profuse shear band formation. Annealing of the 90% cold-rolled material at 800 °C resulted in the formation of a duplex microstructure composed of two different phases with equiaxed morphologies, having significant resistance to grain growth up to 1200 °C. The annealed materials showed disordered FCC and precipitate-free B2 phases. This indicated that quenching of the annealed specimens to room temperature was sufficient to prevent the ordering of the L12 phase and the formation of the Cr-rich nano-precipitates which were dissolved in the B2 phase during annealing. Significant improvement in tensile properties compared to the as-cast alloy could be achieved by thermo-mechanical processing. All the specimens annealed at 800 °C to 1200 °C were having good tensile ductility over 10% as well as high tensile strength greater than 1000 MPa. These indicated that the properties of the EHEA could be successfully tailored using thermo-mechanical processing for a wide range of engineering applications.
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| 10. |
- Wani, I. S., et al.
(författare)
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Ultrafine-Grained AlCoCrFeNi2.1 Eutectic High-Entropy Alloy
- 2016
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Ingår i: Materials Research Letters. - : Informa UK Limited. - 2166-3831. ; 4:3, s. 174-179
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Tidskriftsartikel (refereegranskat)abstract
- The development of microstructure and mechanical properties was investigated in a heavily cold-rolled and annealed AlCoCrFeNi2.1 high-entropy alloy. The as-cast alloy having a eutectic morphology consisting of alternate bands of ordered L1(2) and B2 phases was 90% cold-rolled. The deformed microstructure showed profuse shear banding and disordering of the L12, but no transformation of the B2 phase. A duplex microstructure consisting of ultrafine equiaxed grains (similar to 0.60 mu m) of disordered face centered cubic and B2 was observed after annealing at 800 degrees C. The annealed material showed remarkable strength-ductility combination having ultimate tensile strength similar to 1.2 GPa and elongation to failure similar to 12%.
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