On the Experimental Assessment of Thermodynamic Stability of Nanostructured Solid Solutions

n/

Modeling of point defects annihilation in multilayered cu/nb composites under irradiation

This work focuses on a mathematical modeling of the response to irradiation of a multilayer composite material. Nonstationary balance equations are utilized to account for production, recombination, transport, and annihilation, or removal, of vacancies and interstitials at interfaces. Although the model developed has general validity, Cu/Nb multilayers are used as case study. Layer thickness, temperature, radiation intensity, and surface recombination coefficients were varied systematically to investigate their effect on point defect annihilation processes at interfaces. It is shown that point defect annihilation at interfaces mostly depends on point defect diffusion. The ability of interfaces to remove point defects can be described by a simple map constructed using only two dimensionless parameters, which provides a general tool to estimate the efficiency of vacancy and interstitial removal in multilayer composite materials

Simultaneous spark plasma synthesis and consolidation of WC/Co composites

The single-step synthesis and densification of the WC-6Co cemented carbide starting from elemental powders was obtained by the spark plasma sintering (SPS) technique. The operating conditions that guarantee the complete conversion of the reactants to the desired full dense material have been identified. Specifically, under the application of 800 A and a mechanical pressure of 40 MPa for about 200 s, a product with relative density higher than 99%, hardness of 14.97 ± 0.35 GPa, and 12.5 ± 1.0 MPa m0.5 fracture toughness was obtained. A kinetic investigation of the SPS process was also performed. It revealed that an intermediate phase, i.e., W2C, is the first carbide formed during the carburization process. It was observed that the synthesis and sintering stages take place simultaneously. It was also found that as the applied pulsed current intensity was augmented, the synthesis/sintering time required decreased significantly

Self-healing ability assessment of irradiated multilayered composites: A continuum approach

Atomistic simulations have revealed an unconventional behavior of point defects at interfaces found in multilayer composites synthesized by physical vapor deposition but the observed mechanisms that involve point-defect annihilation are subject to time-scale limitations. So, a mathematical model that describes long-term evolution of point defects in such materials under irradiation is presented in this work. Firstly, the effect of interface point-defect trapping and recombination mechanisms on point-defect concentrations has been studied. In addition, the effect of interface self-interstitial atoms loading, which has been seen during collision cascades, and constitutional vacancies has been studied too. Two interface configurations have been considered between metals in a β-α-β three-layer system (α = Cu and β = Nb, or V), KSmin and KS1. These interfaces correspond to ground-state and defect-free KS structures respectively. The respond to irradiation of the systems investigated here, Cu/Nb and Cu/V, depends on both, interface characteristics and bulk properties. Nonetheless, the influence of the properties of one metal in the point-defect evolution of the other metal is only effective if there are constitutional vacancies at the interface, i.e., for KSmin. Especial attention has been paid to the behavior of the same metal (Cu) when it is surrounded by diverse metals (Nb, or V) with the aim of comparing quantitatively our model predictions with experimental results reported elsewhere. The lower concentration of vacancies in Cu layer of Cu/Nb system at steady state is due to the low mobility of vacancies in niobium.European Social Fund, Operational Programme of Castilla y León, and Junta de Castilla y León, through the Ministry of Education, as well as by the European Union Framework Programme 7, Multiscale Modelling and Materials by Design of Interface-Controlled Radiation Damage in Crystalline Materials (RADINTERFACES) under grant agreement no. 26327

Role of interface in multilayered composites under irradiation: A mathematical investigation

A continuum model of point-defects evolution during irradiation of a multilayer composite material is presented in this work. Nonstationary balance equations are used to describe production, recombination, transport, and annihilation, or removal, of vacancies and interstitials in a β-α-β three-layer system (α = Cu and β = Nb, V, or Ni). In addition, transport and trapping of point-defects at interfaces are taken into account. Numerical investigation on similarities and differences between Cu/Nb, Cu/V, and Cu/Ni systems is also performed. A general comparison of model results reveals that average vacancy concentration is typically higher than SIA one in both layers for all the systems investigated. This is a consequence of the higher diffusion rate of SIAs with respect to vacancies. Stationary state is reached without saturating interface point-defect traps by all systems but Cu/Ni for the case of SIAs. It can be also seen that Cu/Nb and Cu/V systems have a very similar behavior regarding point-defect temporal evolution in copper (layer α), while higher SIA concentration at steady state is shown therein by the Cu/Ni structure. Moreover, Cu/V system displays the lower stationary vacancy concentration in layer β.European Social Fund, Operational Programme of Castilla y Le´on, and Junta de Castilla y Le´on, through theMinistry of Education, as well as by the EuropeanUnion Framework Programme 7,Multiscale Modelling and Materials by Design of Interface-Controlled Radiation Damage in Crystalline Materials (RADINTERFACES) under Grant Agreement no. 26327

Toxicological assessment of nanocrystalline metal alloys with potential applications in the aeronautical field

The development of new candidate alloys with outstanding characteristics for their use in the aeronautical field is one of the main priorities for the sector. In this context, nanocrystaline (nc) alloys are considered relevant materials due to their special features, such as their exceptional physical and mechanical properties. However, another important point that needs to be considered with newly developed alloys is the potential toxicological impact that these materials may have in humans and other living organisms. The aim of this work was to perform a preliminary toxicological evaluation of three nc metal alloys (WCu, WAl and TiAl) in powder form produced by mechanical alloying, applying different in vitro assays, including a mix of W-Cu powders with standard grain size in the experiments to stablish comparisons. The effects of the direct exposure to powder suspensions and/or to their derived leachates were analysed in three model organisms representative of human and environmental exposures (the adenocarcinomic human alveolar basal epithelial cell line A549, the yeast Saccharomyces cerevisiae and the Gram negative bacterium Vibrio fischeri). Altogether, the results obtained provide new insights about the potential harmful effects of the selected nc alloys, showing that, from a toxicological perspective, nc TiAl is the safest candidate in the model organisms and conditions tested.EU Horizon 2020 projects ICARUS (H2020-FETOPEN-2014-2015-RIA, grant agreement N° 713514) and ICARUS-INAS (FETOPEN-03-2018-2019-2020, Grant agreement N° 946174)

Dense nanocrystalline W alloys: Enhancement of hardness and thermal stability by Al addition

Nanocrystalline W100-xAlx (x up to 20 at.%) powders obtained by mechanical alloying have been consolidated by spark plasma sintering (SPS). Alloying W with Al significantly improves the sinterability, allowing the fabrication of dense samples. The consolidation process keeps the nanocrystalline microstructure substantially unaffected, which contributes to the hardness of the final W-Al alloys. The room-temperature nano-and micro-hardness of dense W80Al20 alloy sintered at 1100 degrees C are as high as 18 and 14 GPa, respectively. These values are significantly higher than those previously reported for pure coarse-or submicron-grained W and may be ultimately ascribed to the grain boundary segregation of Al

Complicated enterocele: timely resolution with bowel resection via a vaginal approach: case report

Background: Enterocele is an uncommon, serious condition that requires accurate and early diagnosis to prevent complications such as intestinal obstruction, incarceration, and strangulation, with consequent intestinal ischemia, necrosis, and evisceration. We report a rare case of a patient with a voluminous enterocele and initial signs of intestinal ischemia who underwent urgent vaginal surgery. Case description: An 80-year-old woman presented with a voluminous mass protruding from the vagina, associated abdominopelvic pain, a 10-day history of bowel sub-occlusion, and numerous episodes of profuse vaginal bleeding. She was diagnosed with an enterocele with early signs of complications. Owing to her advanced clinical condition and comorbidities, we opted for an urgent vaginal procedure. Intestinal loops with initial signs of ischemia were resected via a transvaginal approach, leading to good clinical outcomes. She was discharged on postoperative day 5. Conclusions: This rare case highlights a surgical emergency that was managed with transvaginal resection of the intestine. Early identification of the initial signs of complications allowed for this less invasive approach, resulting in reduced morbidity and length of hospital stay

SINTESI E SIMULTANEA DENSIFICAZIONE DI INTERMETALLICI MEDIANTE SINTERIZZAZIONE IN CORRENTE PULSATA

Sono state evidenziate alcune delle più recenti applicazioni in campo metallurgico della sinterizzazione attivata mediante corrente elettrica pulsata, SCP, meglio nota con l’acronimo inglese SPS (“Spark Plasma Sintering”). In particolare l’attenzione è stata focalizzata sull’impiego di tale tecnica per la sintesi e simultanea densificazione dei sistemi intermetallici NiTi e NbAl3 a partire da polveri dei metalli elementari. Nel caso della lega equiatomica NiTi, è stato dimostrato che, attraverso un processo ad un solo stadio, la tecnica SCP consente l’ottenimento di un prodotto finale già caratterizzato da un elevato grado di purezza (5.8-7.2 mol% di NiTi2) ed una elevata densità relativa (99%), più rapidamente (20 min) rispetto ai tempi richiesti dai processi convenzionali della metallurgia delle polveri. Sono state inoltre analizzate le potenzialità della combinazione di tecniche di attivazione meccanica con il processo SCP. Attraverso una opportuna analisi dell’effetto dei principali parametri operativi di entrambe le tecniche è stato possibile l’ottenimento di un prodotto NbAl3 puro e caratterizzato da densità molto elevate (97.5 ± 2.5% rispetto a quella teorica)

Can Urine Metabolomics Be Helpful in Differentiating Neuropathic and Nociceptive Pain? A Proof-of-Concept Study

The diagnosis of pain nature is a troublesome task and a wrong attribution often leads to an increase of costs and to avoidable pharmaceutical adverse reactions. An objective and specific approach to achieve this diagnosis is highly desirable. The aim of this work was to investigate urine samples collected from patients suffering from pain of different nature by a metabolomics approach based on 1 H NMR spectroscopy and multivariate statistical analysis. We performed a prospective study on 74 subjects: 37 suffering from pain (12 with nociceptive and 25 with neuropathic pain), and 37 controls not suffering from any kind of chronic pain. The application of discriminant analysis on the urine spectral profiles allowed us to classify these two types of pain with high sensibility and specificity. Although the classification relies on the global urine metabolic profile, the individual contribution in discriminating neuropathic pain patients of metabolites such as choline and phosphocholine, taurine and alanine, suggests potential lesions to the nervous system. To the best of our knowledge, this is the first time that a urine metabolomics profile is used to classify these two kinds of pain. This methodology, although based on a limited sample, may constitute the basis for a new helpful tool in the clinical diagnosis