Evolution of microstructure and hardness in an AZ80 magnesium alloy processed by high-pressure torsion

An AZ80 magnesium alloy with an initial grain size of ?25 ?m and a hardness of Hv ? 63 was processed by high-pressure torsion (HPT) at room temperature for up to 10 turns under an imposed pressure of 6.0 GPa. After processing, the specimens were examined by optical microscopy and transmission electron microscopy and measurements were taken of the Vickers microhardness along diameters of the HPT discs. The results show that the grains are refined to ?200 nm after 5 and 10 turns of HPT and the hardness increases to Hv ? 120 at an equivalent strain of ?30. There is a saturation condition and no further hardening at additional equivalent strains up to >200

Severely plastically deformed AZ80 magnesium alloy: microstructure and mechanical properties

In this study the evolution of microstructure and the mechanical properties of an AZ80 magnesium alloy were investigated. It examined prepared samples of AZ80 magnesium alloy before and after processing by severe plastic deformation (SPD) using the High-Pressure Torsion (HPT) technique.An AZ80 magnesium alloy with a chemical composition of Mg-8.7% Al-0.5% Zn was processed using HPT. The processing was conducted at room temperature, 296 K, and at the elevated temperature of 473 K under quasi-constrained conditions, using an imposed pressure of 6.0 GPa at a speed of one revolution per minute (rpm) through different numbers of turns: 1/4, 1, 3, 5 and 10. Processing magnesium alloy by HPT produced excellent grain refinement in the alloy, and it prevented the samples from developing cracks and segmentation at ambient temperature better than the other popular technique of SPD, for instance Equal-Channel Angular Pressing (ECAP).The initial microstructure and the microstructural development after HPT processing were subsequently examined by optical microscopy (OM), scanning electron microscopy (SEM) and Transmission Electron microscopy (TEM). Microstructural investigations for the as-received condition showed an average grain size of ~25 m. Optical microscopy images revealed microstructural evolution at both room and elevated temperature after the HPT process. The small proportion of refined grains at the edges expanded towards the disc centre with consecutive increasing numbers of revolutions. The TEM images demonstrate an evolution toward homogeneity at increasing numbers of revolutions. The final average grain size after 10 turns when the alloy was processed at room temperature was ~200 nm and ~330 nm when the alloy was processed by HPT at 473 K. The selected area electron diffraction (SAED) images of HPT samples after 10 revolutions show a fully developed ring at room temperature, indicating a microstructure with high angles of misorientation grain boundaries, and a less developed ring at 473 K. Microstructural observation through the disc thickness demonstrates more heterogeneity in the vertical than the radial direction.Vickers microhardness (Hv) values were taken along the disc diameter (radial direction) and over the total surface of the discs (colour-coded contour mapping). The results of Vickers microhardness (Hv) measurements along the diameters of the discs verify the heterogeneity of HPT deformation at lower numbers of turns. In the samples, the microhardness values increased rapidly at the edges of the disc, while the centres showed a lower value, and this large difference confirms the heterogeneity of HPT deformation in the early stages. With further straining samples showed a significant increase in microhardness values from the edges towards the disc centre. The microhardness values of samples processed by 5 and 10 turns showed a reasonable homogeneity across the disc diameter, with an average value of ~120 Hv when AZ80 was processed at room temperature and an average value of ~110 Hv when processed at 473 K.Likewise, three selected discs processed by HPT for 1, 3 and 10 turns at both 296 K and 473 K were sectioned vertically across their diameter to be tested by (OM) and Vickers microhardness (Hv) through their thickness (axial direction). The results of (OM) and Vickers microhardness (Hv) confirmed the high heterogeneity in the axial direction than the radial direction.Subsequent to the HPT process at room temperature, tensile specimens were cut from the processed discs and pulled in tension to failure at different tensile test temperatures (473, 523 and 573 K) and strain rates of (1.4×10-4 s-1, 1.4×10-3 s-1, 1.4×10-2 s-1 and 1.4×10-1 s-1). The superplasticity of AZ80 magnesium alloy was confirmed for the first time (to the author’s knowledge) at a maximum elongation of 645% when the alloy was pulled in tension to failure at 573 K using strain rate of 1.4×10-4 s-1. Moreover, the alloy exhibited a lower temperature superplasticity when it attained 423% at 473 K. Despite this superplasticity, AZ80 magnesium alloy does not show the predicted behaviour of increasing ductility with increased imposed strain during HPT process and decreased average grain size. The maximum elongation was reached in a sample processed by HPT for one turn, in which a smaller average grain size and the homogenous microstructure were not achieved

Hardness homogeneity in an AZ80 magnesium alloy processed by high-pressure torsion

Experiments were conducted on an AZ80 magnesium alloy by processing by high-pressure torsion (HPT) at room temperature (296 K) for up to 10 turns under an imposed pressure of 6.0 GPa. Measurements of the Vickers microhardness along diameters and through the disk thicknesses were recorded after HPT to evaluate the evolution towards homogeneity. The results show hardness increases up to a factor of approximately 2 and the deformation is more homogeneous along the disc diameter than through the thickness

Hardness evolution of AZ80 magnesium alloy processed by HPT at different temperatures

Discs of an extruded AZ80 magnesium alloy were processed by high-pressure torsion (HPT) using 6.0 GPa up to 10 turns at different temperatures (296 K and 473 K). The disc surfaces and cross-sectional planes were examined before and after processing using optical microscopy and Vickers microhardness (Hv). The microhardness results at the surface show differences in the strength of the material as a function of distance from the disc centres up to saturation, as well as a function of distance from the bottom to the surface in the cross-sectional plane. This study analyses the effect of processing temperature on the evolution of microhardness of AZ80 magnesium alloy processed by high-pressure torsion

Achieving superplastic elongations in an AZ80 magnesium alloy processed by high-pressure torsion

Processing magnesium alloy by High-Pressure Torsion (HPT) is a technique used successfully to refine the grains of an alloy to the submicrometer and nanometer scale to produce an ultrafine grained microstructure. Grain refinement can improve the mechanical properties of magnesium alloys as well as enhancing its ductility and providing a potential for exhibiting superplastic behaviour at elevated temperature. Research was conducted to process the AZ80 magnesium alloy by HPT at room temperature for different numbers of turns with the microstructures before and after HPT critically investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Vickers microhardness (Hv) tests. Subsequently, tensile specimens were cut from the processed disks and pulled in tension to failure at temperatures of 473, 523 and 573 K and at strain rates in the range from 1.4 × 10 4 to 1.4 × 10-¬1 s-1. The introduction of superplasticity in the AZ80 magnesium alloy when processing by HPT was demonstrated for the first time with a maximum elongation of 645% at a testing temperature of 573 K. There was also evidence for low temperature superplasticity with an elongation of 423% at 473 K. The dominant mechanism for superplastic flow was grain boundary sliding with a strain rate sensitivity of m ≈ 0.5 and an activation energy of Q ≈ 73 kJ mol-1

Phytochemicals from Leucas zeylanica Targeting Main Protease of SARS-CoV-2: Chemical Profiles, Molecular Docking, and Molecular Dynamics Simulations

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a contemporary coronavirus, has impacted global economic activity and has a high transmission rate. As a result of the virus’s severe medical effects, developing effective vaccinations is vital. Plant-derived metabolites have been discovered as potential SARS-CoV-2 inhibitors. The SARS-CoV-2 main protease (Mpro) is a target for therapeutic research because of its highly conserved protein sequence. Gas chromatography–mass spectrometry (GC-MS) and molecular docking were used to screen 34 compounds identified from Leucas zeylanica for potential inhibitory activity against the SARS-CoV-2 Mpro. In addition, prime molecular mechanics–generalized Born surface area (MM-GBSA) was used to screen the compound dataset using a molecular dynamics simulation. From molecular docking analysis, 26 compounds were capable of interaction with the SARS-CoV-2 Mpro, while three compounds, namely 11-oxa-dispiro[4.0.4.1]undecan-1-ol (−5.755 kcal/mol), azetidin-2-one 3,3-dimethyl-4-(1-aminoethyl) (−5.39 kcal/mol), and lorazepam, 2TMS derivative (−5.246 kcal/mol), exhibited the highest docking scores. These three ligands were assessed by MM-GBSA, which revealed that they bind with the necessary Mpro amino acids in the catalytic groove to cause protein inhibition, including Ser144, Cys145, and His41. The molecular dynamics simulation confirmed the complex rigidity and stability of the docked ligand–Mpro complexes based on the analysis of mean radical variations, root-mean-square fluctuations, solvent-accessible surface area, radius of gyration, and hydrogen bond formation. The study of the postmolecular dynamics confirmation also confirmed that lorazepam, 11-oxa-dispiro[4.0.4.1]undecan-1-ol, and azetidin-2-one-3, 3-dimethyl-4-(1-aminoethyl) interact with similar Mpro binding pockets. The results of our computerized drug design approach may assist in the fight against SARS-CoV-2

Surgical site infection after gastrointestinal surgery in children: An international, multicentre, prospective cohort study

Introduction Surgical site infection (SSI) is one of the most common healthcare-associated infections (HAIs). However, there is a lack of data available about SSI in children worldwide, especially from low-income and middle-income countries. This study aimed to estimate the incidence of SSI in children and associations between SSI and morbidity across human development settings. Methods A multicentre, international, prospective, validated cohort study of children aged under 16 years undergoing clean-contaminated, contaminated or dirty gastrointestinal surgery. Any hospital in the world providing paediatric surgery was eligible to contribute data between January and July 2016. The primary outcome was the incidence of SSI by 30 days. Relationships between explanatory variables and SSI were examined using multilevel logistic regression. Countries were stratified into high development, middle development and low development groups using the United Nations Human Development Index (HDI). Results Of 1159 children across 181 hospitals in 51 countries, 523 (45·1%) children were from high HDI, 397 (34·2%) from middle HDI and 239 (20·6%) from low HDI countries. The 30-day SSI rate was 6.3% (33/523) in high HDI, 12·8% (51/397) in middle HDI and 24·7% (59/239) in low HDI countries. SSI was associated with higher incidence of 30-day mortality, intervention, organ-space infection and other HAIs, with the highest rates seen in low HDI countries. Median length of stay in patients who had an SSI was longer (7.0 days), compared with 3.0 days in patients who did not have an SSI. Use of laparoscopy was associated with significantly lower SSI rates, even after accounting for HDI. Conclusion The odds of SSI in children is nearly four times greater in low HDI compared with high HDI countries. Policies to reduce SSI should be prioritised as part of the wider global agenda

SARS-CoV-2 vaccination modelling for safe surgery to save lives: data from an international prospective cohort study

Background: Preoperative SARS-CoV-2 vaccination could support safer elective surgery. Vaccine numbers are limited so this study aimed to inform their prioritization by modelling. Methods: The primary outcome was the number needed to vaccinate (NNV) to prevent one COVID-19-related death in 1 year. NNVs were based on postoperative SARS-CoV-2 rates and mortality in an international cohort study (surgical patients), and community SARS-CoV-2 incidence and case fatality data (general population). NNV estimates were stratified by age (18-49, 50-69, 70 or more years) and type of surgery. Best- and worst-case scenarios were used to describe uncertainty. Results: NNVs were more favourable in surgical patients than the general population. The most favourable NNVs were in patients aged 70 years or more needing cancer surgery (351; best case 196, worst case 816) or non-cancer surgery (733; best case 407, worst case 1664). Both exceeded the NNV in the general population (1840; best case 1196, worst case 3066). NNVs for surgical patients remained favourable at a range of SARS-CoV-2 incidence rates in sensitivity analysis modelling. Globally, prioritizing preoperative vaccination of patients needing elective surgery ahead of the general population could prevent an additional 58 687 (best case 115 007, worst case 20 177) COVID-19-related deaths in 1 year. Conclusion: As global roll out of SARS-CoV-2 vaccination proceeds, patients needing elective surgery should be prioritized ahead of the general population