Effect of holding time, thickness and heat treatment on microstructure and mechanical properties of compacted graphite cast iron

The effect of holding time, thickness and annealing heat treatment on the microstructure and some mechanical properties of compacted graphite iron (CGI) are studied. Samples of CGI are produced in Helwan factory for casting by using GGG 70 as base metal in a medium frequency induction furnace. The mechanical properties (tensile strength, and hardness) of the as-cast and after heat treatment samples are determined and the microstructure of the samples is examined using optical microscope. The results show that the mechanical properties and microstructure of CGI depend on holding time, thickness and annealing heat treatment; it is found that increasing the holding time from 10 min to 17 min results in lowering the Mg content from 0.031% to 0.021% and as a result lower nodularity was obtained. Lowering the thickness from 20 mm to 5 mm increases the tendency of dendritic structure as a result of increasing the cooling rate. The annealed samples with mainly ferritic matrix gave the lowest tensile strength and hardness value compared with the as-cast conditions. Keywords: Compacted graphite iron (CGI), Heat treatment, Microstructures, Mechanical propertie

Mechanical behavior and corrosion properties of Ti-7Mo-8Nb alloy for biomedical applications

The present study investigates the microstructural, mechanical and corrosion properties of Ti-7Mo-8Nb alloy manufactured through powder metallurgy. The performance of the developed alloy is benchmarked against cast Ti-6Al-4V. Microstructure examination of Ti-7Mo-8Nb revealed a Widmanstätten structure containing equiaxed β grains along with acicular α phase. In regards to the mechanical properties, Ti-7Mo-8Nb possessed higher compressive yield strength, higher hardness but lower elastic modulus than Ti-6Al-4V. The elastic modulus of Ti-7Mo-8Nb was almost 44.9 GPa, approaching the usually desired value of 30 GPa for cortical bone. Wear test revealed also a lower wear rate for Ti-7Mo-8Nb. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) experiments were carried out for both Ti-7Mo-8Nb and Ti-6Al-4V immersed in Hank’s solution as a simulated body fluid at a temperature of 37 °C. Both experiments revealed higher corrosion resistance for Ti-7Mo-8Nb manifested by lower corrosion and passivation current densities, higher negative phase angle, higher impedance modulus and larger Nyquist semicircle diameter as compared to Ti-6Al-4V alloy. The superior corrosion properties of Ti-7Mo-8Nb are indicative of the development of a more stable passive layer on the surface. The fitting of EIS data into an equivalent circuit suggested the formation of a double oxide layer consisting of an inner compact base passive film along with an external porous layer. The presented combination of high strength, high corrosion resistance along with low elastic modulus puts forward the Ti-7Mo-8Nb alloy as a good candidate for orthopedic biomedical applications

The burden of metabolic risk factors in North Africa and the Middle East, 1990–2019: findings from the Global Burden of Disease StudyResearch in context

Summary: Background: The objective of this study is to investigate the trends of exposure and burden attributable to the four main metabolic risk factors, including high systolic blood pressure (SBP), high fasting plasma glucose (FPG), high body-mass index (BMI), and high low-density lipoproteins cholesterol (LDL) in North Africa and the Middle East from 1990 to 2019. Methods: The data were retrieved from Global Burden of Disease Study 2019. Summary exposure value (SEV) was used for risk factor exposure. Burden attributable to each risk factor was incorporated in the population attributable fraction to estimate the total attributable deaths and disability-adjusted life-years (DALYs). Findings: While age-standardized death rate (ASDR) attributable to high-LDL and high-SBP decreased by 26.5% (18.6–35.2) and 23.4% (15.9–31.5) over 1990–2019, respectively, high-BMI with 5.1% (−9.0–25.9) and high-FPG with 21.4% (7.0–37.4) change, grew in ASDR. Moreover, age-standardized DALY rate attributed to high-LDL and high-SBP declined by 30.2% (20.9–39.0) and 25.2% (16.8–33.9), respectively. The attributable age-standardized DALY rate of high-BMI with 8.3% (−6.5–28.8) and high-FPG with 27.0% (14.3–40.8) increase, had a growing trend. Age-standardized SEVs of high-FPG, high-BMI, high-SBP, and high-LDL increased by 92.4% (82.8–103.3), 76.0% (58.9–99.3), 10.4% (3.8–18.0), and 5.5% (4.3–7.1), respectively. Interpretation: The burden attributed to high-SBP and high-LDL decreased during the 1990–2019 period in the region, while the attributable burden of high-FPG and high-BMI increased. Alarmingly, exposure to all four risk factors increased in the past three decades. There has been significant heterogeneity among the countries in the region regarding the trends of exposure and attributable burden. Urgent action is required at the individual, community, and national levels in terms of introducing effective strategies for prevention and treatment that account for local and socioeconomic factors. Funding: Bill & Melinda Gates Foundation