Effect of alloying elements on the Sr modification of Al-Si cast alloys

Strontium-based modifier alloys are commonly adopted to modify the eutectic silicon in aluminum-silicon casting alloys by changing the silicon shape from an acicular to a spherical form. Usually, the modifier alloy necessary to properly change the silicon shape depends on the silicon content, but the alloying elements’ content may have an influence. The AlSr10 master alloy’s modifying effect was studied on four Al-Si alloys through the characterization of microstructural and mechanical properties (micro-hardness and impact tests). The experimental results obtained on gravity cast samples highlighted the interdependence in the modification of silicon between the Si content and the alloying elements. After modification, a higher microstructural homogeneity characterized by a reduction of up to 22.8% in the size of intermetallics was observed, with a generalized reduction in secondary dendritic arm spacing. The presence of iron-based polygonal-shaped intermetallics negatively affects Sr modification; coarser silicon particles tend to grow close to α-Fe. The presence of casting defects such as bifilm reduces Sr modification’s beneficial effects, and little increase in absorbed impact energy is observed in this work

Residual stress analysis applied to HPDC aluminium components: a case study

High-Pressure Die Casting (HPDC) is a casting process largely diffused in the aluminium foundries. By HPDC is possible to obtain aluminium castings with thin walls and high specific mechanical properties in short cycle times. Aluminium HPDC castings are commonly intended for the automotive sector: engine, covers, engine blocks and more in general the powertrain. In recent years, one of the most important focus in the automotive sector is decreasing the powertrain weight, acting on stock allowances in certain parts of the casting. This reduction can affect the dimensional features and in turn the residual stress inside the casting. Despite that, it is possible to obtain beneficial compression states into the castings by mean of post-process operations, such as shot-blasting, to reduce or remove residual stresses by mean of heat treatments. Residual stresses can be assessed by an X-Ray residual stress measurement device, a nondestructive technique that allows observing the process parameters effect into the casting. In this work, after a detailed analysis of the residual stress measurement available for aluminium castings, a powertrain component realized in aluminium alloy EN AC 46000 was analysed. These analyses involved both dimensional response and related residual stresses in the as-cast state and the shot-blasted-state on a valve cover, to understand and prevent the residual stress states into the aluminium castings

Backscattered electron images, X-ray maps and Monte Carlo simulations applied to the study of plagioclase composition in volcanic rocks

Zoning patterns in plagioclases are related to abrupt changes in the anorthite content along the crystal growing direction. Accurate characterization of these patterns by electron microprobe is useful to identify magma chamber processes such as recharge, mingling and whole-chamber overturn events. In this work, a new procedure to obtain high resolution quantitative maps of anorthite concentration in single plagioclase crystals is developed. The methodology consists in performing a calibration of backscattered electron images using quantitative X-ray maps. The ultimate resolution of charac- teristic X-rays and backscattered electron signals is studied by Monte Carlo simulation. The method is applied to characterize the chemical composition of a volcanic plagioclase from the Cerro Vilama, Argentina. The results obtained are more precise than the values given by the methods commonly used in the study of plagioclase composition, i.e. the classical profiling by electron microprobe point analysis or the modern backscattered electron image calibration by means of quantitative energy or wavelength dispersive X-ray analysis at a few selected points.Facultad de Ingeniería (FI)Laboratorio de Investigaciones de Metalurgia Física (LIMF)Centro de Investigación y Desarrollo en Ciencias Aplicadas (CINDECA

Potential of Manuka Honey as a Natural Polyelectrolyte to Develop Biomimetic Nanostructured Meshes With Antimicrobial Properties

The use of antibiotics has been the cornerstone to prevent bacterial infections; however, the emergency of antibiotic-resistant bacteria is still an open challenge. This work aimed to develop a delivery system for treating soft tissue infections for: (1) reducing the released antimicrobial amount, preventing drug-related systemic side effects; (2) rediscovering the beneficial effects of naturally derived agents; and (3) preserving the substrate functional properties. For the first time, Manuka honey (MH) was proposed as polyelectrolyte within the layer-by-layer assembly. Biomimetic electrospun poly(εcaprolactone) meshes were treated via layer-by-layer assembly to obtain a multilayered nanocoating, consisting of MH as polyanion and poly-(allylamine-hydrochloride) as polycation. Physicochemical characterization demonstrated the successful nanocoating formation. Different cell lines (human immortalized and primary skin fibroblasts, and primary endothelial cells) confirmed positively the membranes cytocompatibility, while bacterial tests using Gram-negative and Gram-positive bacteria demonstrated that the antimicrobial MH activity was dependent on the concentration used and strains tested

Electrodeposited cu thin layers as low cost and effective underlayers for Cu2O photocathodes in photoelectrochemical water electrolysis

Cu2O is one of the most studied semiconductors for photocathodes in photoelectrochemical water splitting (PEC-WS). Its low stability is counterbalanced by good activity, provided that a suitable underlayer/support is used. While Cu2O is mostly studied on Au underlayers, this paper proposes Cu(0) as a low-cost, easy to prepare and highly efficient alternative. Cu and Cu2O can be electrodeposited from the same bath, thus allowing in principle to tune the final material\u2019s physico-chemical properties with high precision with a scalable method. Electrodes and photoelectrodes are studied by means of electrochemical methods (cyclic voltammetry, Pb underpotential deposition) and by ex-situ X-ray absorption spectroscopy (XAS). While the potential applied for the deposition of Cu has no influence on the bulk structure and on the photocurrent displayed by the semiconductor, it plays a role on the dark currents, making this strategy promising for improving the material\u2019s stability. Au/Cu2O and Cu/Cu2O show similar performances, the latter having clear advantages in view of future use in practical applications. The influence of Cu underlayer thickness was also evaluated in terms of obtained photocurrent

Colata per gravità di un FGM in lega di alluminio: ottimizzazione del trattamento termico e proprietà finali

Le leghe di alluminio sono largamente utilizzate nel settore dell’autoveicolo per produrre ad esempio blocchi motore, coperchi punterie, pistoni, grazie all’ottima correlazione tra resistenza meccanica e leggerezza che le contraddistingue. In particolare, i pistoni sono soggetti a fratture per fatica vista la loro duale richiesta di resistenza alla fatica termica e di duttilità lungo l’intero volume del pezzo. I FGM (Functionally Graded Materials) sono materiali compositi avanzati ideati per garantire una graduale variazione di proprietà e composizione lungo il volume del materiale stesso. In questo lavoro, la lega per pistoni EN AC 48000 è impiegata insieme alla lega EN AC 42100 per la realizzazione di un FGM, con l’obiettivo di ottenere una variazione di proprietà lungo il volume del pezzo che garantisca le caratteristiche meccaniche ottimali per un pistone. Le proprietà finali richieste vengono ottenute per mezzo di trattamento termico T6 con solubilizzazione a 530°C ed invecchiamento artificiale a 175°C fornendo caratteristiche meccaniche apprezzabili

Medical-grade silicone coated with rhamnolipid R89 is effective against Staphylococcus spp. Biofilms

Staphylococcus aureus and Staphylococcus epidermidis are considered two of the most important pathogens, and their biofilms frequently cause device-associated infections. Microbial biosurfactants recently emerged as a new generation of anti-adhesive and anti-biofilm agents for coating implantable devices to preserve biocompatibility. In this study, R89 biosurfactant (R89BS) was evaluated as an anti-biofilm coating on medical-grade silicone. R89BS is composed of homologues of the mono- (75%) and di-rhamnolipid (25%) families, as evidenced by mass spectrometry analysis. The antimicrobial activity against Staphylococcus spp. planktonic and sessile cells was evaluated by microdilution and metabolic activity assays. R89BS inhibited S. aureus and S. epidermidis growth with minimal inhibitory concentrations (MIC99) of 0.06 and 0.12 mg/mL, respectively and dispersed their pre-formed biofilms up to 93%. Silicone elastomeric discs (SEDs) coated by R89BS simple adsorption significantly counteracted Staphylococcus spp. biofilm formation, in terms of both built-up biomass (up to 60% inhibition at 72 h) and cell metabolic activity (up to 68% inhibition at 72 h). SEM analysis revealed significant inhibition of the amount of biofilm-covered surface. No cytotoxic effect on eukaryotic cells was detected at concentrations up to 0.2 mg/mL. R89BS-coated SEDs satisfy biocompatibility requirements for leaching products. Results indicate that rhamnolipid coatings are effective anti-biofilm treatments and represent a promising strategy for the prevention of infection associated with implantable devices

Dual-readout Calorimetry

The RD52 Project at CERN is a pure instrumentation experiment whose goal is to understand the fundamental limitations to hadronic energy resolution, and other aspects of energy measurement, in high energy calorimeters. We have found that dual-readout calorimetry provides heretofore unprecedented information event-by-event for energy resolution, linearity of response, ease and robustness of calibration, fidelity of data, and particle identification, including energy lost to binding energy in nuclear break-up. We believe that hadronic energy resolutions of {\sigma}/E $\approx$ 1 - 2% are within reach for dual-readout calorimeters, enabling for the first time comparable measurement preci- sions on electrons, photons, muons, and quarks (jets). We briefly describe our current progress and near-term future plans. Complete information on all aspects of our work is available at the RD52 website http://highenergy.phys.ttu.edu/dream/.Comment: 10 pages, 10 figures, Snowmass White pape

Gestione delle conchiglie nella colata in gravità e possibili vie per migliorarne prestazioni e durata

La colata in gravità è una tecnologia di largo impiego nelle fonderie di alluminio: seppur ben nota è ancora attuale. Nonostante molte ricerche negli ultimi anni si siano focalizzate sullo studio di processi ad elevata produttività come la pressocolata, vi è ancora una larga serie di prodotti che viene ottenuta tramite colata in gravità, grazie a cui è possibile ottenere getti con difettosità ridotta e proprietà meccaniche superiori. Nonostante la colata in gravità sia una tecnologia che non è possibile definire innovativa, l’evoluzione subita dai componenti in termini di geometria, dimensioni e volumi, ha imposto un aumento della produttività a fronte di una riduzione delle tolleranze accettabili. Questi cambiamenti hanno inficiato sulla vita delle conchiglie in acciaio, utensili che si usurano sempre più facilmente. Per ottimizzare il processo produttivo è necessario introdurre su questa tecnologia già conosciuta degli elementi innovativi. In questo studio è presentato lo stato dell’arte dei metodi per aumentare la vita delle conchiglie nella colata in gravità con particolare attenzione all’effetto della rugosità superficiale della conchiglia e del metodo di verniciatura sulla resistenza ad usura ed alla metallizzazione dell’acciaio. L’alluminio fuso infatti, durante il processo di colata, interagisce con l’acciaio di cui è costituita la conchiglia, producendo usura da erosione e metallizzazione delle superfici con cui entra in contatto. Per limitare il danneggiamento della conchiglia si utilizzano comunemente delle vernici, al fine di creare una barriera tra i due materiali. Tuttavia il processo di verniciatura spesso viene effettuato basandosi su principi qualitativi e troppo spesso semi-quantitativi. Questo studio vuole investigare in modo più approfondito le fasi da seguire per l’ottenimento di una verniciatura ottimale, andando a utilizzare differenti vernici commerciali e valutandone la loro resistenza sia dal punto di vista sia della finitura superficiale della conchiglia che della resistenza alle alte temperature, simulando le condizioni d’uso reali della conchiglia, attraverso prove di usura e prove di immersione in alluminio fuso