Effect of Graphene addition on the mechanical and tribological behavior of nanostructured AA2124 /Graphene self-lubricating metal matrix composite

In the current research, the mechanical and tribological behavior, and structural evolution of AA2124-3 and 5-wt.% graphene (G) composites prepared by a combination of ball milling and hot extrusion were investigated. Mixing followed by energy ball milling of the powders was conducted under argon atmosphere. Hot extrusion of the green compacts was carried out at 0.46 and 0.68 of the alloy melting temperature. Properties such as macro and micro-hardness, nanohardness, tensile and lattice strain were characterized. Wear rates, coefficient of friction (COF) were characterized using dry pin-on-disc test under loads of 50, 100N and 150N. Nanoscratch testing were employed to investigate the self-lubricating tribological behavior. X-ray diffraction, optical and scanning electron microscopy were used to determine the influence of the G-content on the crystallite size variation and the lattice strain for the ball milled powders compared to the hot extruded rods. Density measurements and optical microscopy (OM) were employed to investigate the consolidation degree and porosity variation as a function of increasing G- of the G and Al-matrices for the variable conditions. Bulk texture variation was analyzed to evaluate the influence of the extrusion temperature. AA 2124-3 wt.% G composites displayed the highest tensile properties, highest hardness and lowest wear rates and COF, as well as lowest scratch width and depth compared to the 5 wt.%G and the plain alloy. The uniform distribution of the G-particles within the Al-matrices for the 3wt.% containing composites hindered grain coarsening by the induced lattice strain compared to that of 5 wt% G ones. Moreover, addition of 3 wt.% G smeared thin uniform tribofilm on the surfaces of the worn composite rods. The formed layer reduced friction and wear. Increasing the G content up to 5 wt.% resulted in segregation and clustering of the G-particles within the Al-matrices, which caused microplouging and sever plastic deformation wear mechanism and excessive delamination. IV Lower consolidation temperatures of 300oC produced composites with lower wear rates due to the excessive strain hardening effect. Extrusion at 300oC produced a continuous G-encapsulating layer around the Al-matrix compared to an interrupted G-layer for the 450oC extrusions. The G-layer morphology influenced the dominating mechanism of the composite during deformation. Texture analysis of the AA2124-3 wt.%G extruded at low and high temperatures proved that both the Cu-and Shear are the dominating texture components, while increased texture intensities from 1.2-to-1.76 occurred with increasing the extrusion temperature

Mortality from gastrointestinal congenital anomalies at 264 hospitals in 74 low-income, middle-income, and high-income countries: a multicentre, international, prospective cohort study

Summary Background Congenital anomalies are the fifth leading cause of mortality in children younger than 5 years globally. Many gastrointestinal congenital anomalies are fatal without timely access to neonatal surgical care, but few studies have been done on these conditions in low-income and middle-income countries (LMICs). We compared outcomes of the seven most common gastrointestinal congenital anomalies in low-income, middle-income, and high-income countries globally, and identified factors associated with mortality. Methods We did a multicentre, international prospective cohort study of patients younger than 16 years, presenting to hospital for the first time with oesophageal atresia, congenital diaphragmatic hernia, intestinal atresia, gastroschisis, exomphalos, anorectal malformation, and Hirschsprung’s disease. Recruitment was of consecutive patients for a minimum of 1 month between October, 2018, and April, 2019. We collected data on patient demographics, clinical status, interventions, and outcomes using the REDCap platform. Patients were followed up for 30 days after primary intervention, or 30 days after admission if they did not receive an intervention. The primary outcome was all-cause, in-hospital mortality for all conditions combined and each condition individually, stratified by country income status. We did a complete case analysis. Findings We included 3849 patients with 3975 study conditions (560 with oesophageal atresia, 448 with congenital diaphragmatic hernia, 681 with intestinal atresia, 453 with gastroschisis, 325 with exomphalos, 991 with anorectal malformation, and 517 with Hirschsprung’s disease) from 264 hospitals (89 in high-income countries, 166 in middleincome countries, and nine in low-income countries) in 74 countries. Of the 3849 patients, 2231 (58·0%) were male. Median gestational age at birth was 38 weeks (IQR 36–39) and median bodyweight at presentation was 2·8 kg (2·3–3·3). Mortality among all patients was 37 (39·8%) of 93 in low-income countries, 583 (20·4%) of 2860 in middle-income countries, and 50 (5·6%) of 896 in high-income countries (p<0·0001 between all country income groups). Gastroschisis had the greatest difference in mortality between country income strata (nine [90·0%] of ten in lowincome countries, 97 [31·9%] of 304 in middle-income countries, and two [1·4%] of 139 in high-income countries; p≤0·0001 between all country income groups). Factors significantly associated with higher mortality for all patients combined included country income status (low-income vs high-income countries, risk ratio 2·78 [95% CI 1·88–4·11], p<0·0001; middle-income vs high-income countries, 2·11 [1·59–2·79], p<0·0001), sepsis at presentation (1·20 [1·04–1·40], p=0·016), higher American Society of Anesthesiologists (ASA) score at primary intervention (ASA 4–5 vs ASA 1–2, 1·82 [1·40–2·35], p<0·0001; ASA 3 vs ASA 1–2, 1·58, [1·30–1·92], p<0·0001]), surgical safety checklist not used (1·39 [1·02–1·90], p=0·035), and ventilation or parenteral nutrition unavailable when needed (ventilation 1·96, [1·41–2·71], p=0·0001; parenteral nutrition 1·35, [1·05–1·74], p=0·018). Administration of parenteral nutrition (0·61, [0·47–0·79], p=0·0002) and use of a peripherally inserted central catheter (0·65 [0·50–0·86], p=0·0024) or percutaneous central line (0·69 [0·48–1·00], p=0·049) were associated with lower mortality. Interpretation Unacceptable differences in mortality exist for gastrointestinal congenital anomalies between lowincome, middle-income, and high-income countries. Improving access to quality neonatal surgical care in LMICs will be vital to achieve Sustainable Development Goal 3.2 of ending preventable deaths in neonates and children younger than 5 years by 2030