Tribological behavior and wear mechanisms of mechanically milled Al5083 alloy and Al5083−5wt.%B4C composite at room temperature and 200°C were discussed.Results revealed that due to the oxidative wear at room tem...Tribological behavior and wear mechanisms of mechanically milled Al5083 alloy and Al5083−5wt.%B4C composite at room temperature and 200°C were discussed.Results revealed that due to the oxidative wear at room temperature,a mechanically mixed layer(MML)was formed to protect the surface of the samples.Under 80 N of load at room temperature,the milled Al5083 and the Al5083−5wt.%B4C samples showed evidence of abrasion with limited volume loss.In this case,the wear rates were 5.8×10−7 and 4.4×10−7 mm3/(m·N),respectively.At 200°C and under 80 N of applied load,severe wear occurred in the milled Al5083 sample,and wear rate reached 10.8×10−7 mm3/(m·N)while the Al5083−5wt.%B4C sample showed mild wear with local 3-body abrasion and the wear rate reached 5.3×10−7 mm3/(m·N).Strengthening mechanisms such as dislocation pinning and the Hall−Petch theory,high hardness and the load transfer effect were crucial in determining the wear behavior of the Al5083−5wt.%B4C composite.On the other hand,the milled Al5083 sample represented a relatively high wear rate at 200°C,which seemed to be related to the local grain growth and a drop in its hardness.展开更多
Microstructural characteristics and mechanical behavior of hot extruded Al5083/B4C nanocomposites were studied.Al5083and Al5083/B4C powders were milled for50h under argon atmosphere in attrition mill with rotational s...Microstructural characteristics and mechanical behavior of hot extruded Al5083/B4C nanocomposites were studied.Al5083and Al5083/B4C powders were milled for50h under argon atmosphere in attrition mill with rotational speed of400r/min.For increasing the elongation,milled powders were mixed with30%and50%unmilled aluminum powder(mass fraction)with meanparticle size of>100μm and<100μm and then consolidated by hot pressing and hot extrusion with9:1extrusion ratio.Hot extrudedsamples were studied by optical microscopy,scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),transmission electron microscopy(TEM),tensile and hardness tests.The results showed that mechanical milling process andpresence of B4C particles increase the yield strength of Al5083alloy from130to566MPa but strongly decrease elongation(from11.3%to0.49%).Adding<100μm unmilled particles enhanced the ductility and reduced tensile strength and hardness,but usingthe>100μm unmilled particles reduced the tensile strength and ductility at the same time.By increasing the content of unmilledparticles failure mechanism changed from brittle to ductile.展开更多
Polycystic ovary syndrome (PCOS) is a complex, multifaceted, heterogeneous disorder, affecting 4% to 18% of reproductive-aged women and is associated with reproductive, metabolic and psychological dysfunction. In this...Polycystic ovary syndrome (PCOS) is a complex, multifaceted, heterogeneous disorder, affecting 4% to 18% of reproductive-aged women and is associated with reproductive, metabolic and psychological dysfunction. In this study we determined the relationship between the time to sleep and serum levels of neurohormones in polycystic ovary syndrome (PCOS). Totally 77 PCO patients(case group) and 97 non-PCOS infertile women (control subjects) participated in this study between February 2012 and February 2013. A PSQI sleep questionnaire was completed by each patient in both groups. PSQI sleep questionnaire score and serum concentration of adrenaline, noradrenaline, melatonin, β-endorphin, cortisol and progesterone were compared in two groups. The results of the study indicate that serum levels of melatonin and β-endorphin were lower in women with PCOS. Serum level of stress hormones, adrenaline and noradrenaline were significantly correlated with patients’ sleep time in study group. Serum level of adrenaline in control group was significantly lower in women who wake up earlier in the morning. All hormones except for cortisol had no significant correlation with PSQI global score in both groups and also the people who sleep less than 8 hours had lower cortisol level. These data showed that changes in cortisol in PCO women were due to damage of disturbed sleep at night. Our preliminary work provided this study with new insight into the interactions between sleep-wake cycles in PCO women with specific sleep patterns.展开更多
基金Authors would like to appreciate the former chief of Faculty of Materials&Manufacturing Processes of the Malek-Ashtar University of Technology,Professor EHSANI and the chief of the Composite Department,Dr.POURHOSSEINI along with the Razi and Kimiazi SEM labs and mechanical properties and SEM labs of Iran University of Science and Technology.Furthermore,the authors would like to thank Professor REZAEI,Ms.HAMIDI,and Ms.DAYYANI,Mr.SA'ADAT,and Mr.ATAEI from Iran University of Science and Technology.Special thanks to Mrs.KESHAVARZ,Ms.HAMEDANIZADEH,Ms.SHABANI,Ms.SHOJAEI and Mr.GANDOMKAR for their help and support.
文摘Tribological behavior and wear mechanisms of mechanically milled Al5083 alloy and Al5083−5wt.%B4C composite at room temperature and 200°C were discussed.Results revealed that due to the oxidative wear at room temperature,a mechanically mixed layer(MML)was formed to protect the surface of the samples.Under 80 N of load at room temperature,the milled Al5083 and the Al5083−5wt.%B4C samples showed evidence of abrasion with limited volume loss.In this case,the wear rates were 5.8×10−7 and 4.4×10−7 mm3/(m·N),respectively.At 200°C and under 80 N of applied load,severe wear occurred in the milled Al5083 sample,and wear rate reached 10.8×10−7 mm3/(m·N)while the Al5083−5wt.%B4C sample showed mild wear with local 3-body abrasion and the wear rate reached 5.3×10−7 mm3/(m·N).Strengthening mechanisms such as dislocation pinning and the Hall−Petch theory,high hardness and the load transfer effect were crucial in determining the wear behavior of the Al5083−5wt.%B4C composite.On the other hand,the milled Al5083 sample represented a relatively high wear rate at 200°C,which seemed to be related to the local grain growth and a drop in its hardness.
文摘Microstructural characteristics and mechanical behavior of hot extruded Al5083/B4C nanocomposites were studied.Al5083and Al5083/B4C powders were milled for50h under argon atmosphere in attrition mill with rotational speed of400r/min.For increasing the elongation,milled powders were mixed with30%and50%unmilled aluminum powder(mass fraction)with meanparticle size of>100μm and<100μm and then consolidated by hot pressing and hot extrusion with9:1extrusion ratio.Hot extrudedsamples were studied by optical microscopy,scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),transmission electron microscopy(TEM),tensile and hardness tests.The results showed that mechanical milling process andpresence of B4C particles increase the yield strength of Al5083alloy from130to566MPa but strongly decrease elongation(from11.3%to0.49%).Adding<100μm unmilled particles enhanced the ductility and reduced tensile strength and hardness,but usingthe>100μm unmilled particles reduced the tensile strength and ductility at the same time.By increasing the content of unmilledparticles failure mechanism changed from brittle to ductile.
文摘Polycystic ovary syndrome (PCOS) is a complex, multifaceted, heterogeneous disorder, affecting 4% to 18% of reproductive-aged women and is associated with reproductive, metabolic and psychological dysfunction. In this study we determined the relationship between the time to sleep and serum levels of neurohormones in polycystic ovary syndrome (PCOS). Totally 77 PCO patients(case group) and 97 non-PCOS infertile women (control subjects) participated in this study between February 2012 and February 2013. A PSQI sleep questionnaire was completed by each patient in both groups. PSQI sleep questionnaire score and serum concentration of adrenaline, noradrenaline, melatonin, β-endorphin, cortisol and progesterone were compared in two groups. The results of the study indicate that serum levels of melatonin and β-endorphin were lower in women with PCOS. Serum level of stress hormones, adrenaline and noradrenaline were significantly correlated with patients’ sleep time in study group. Serum level of adrenaline in control group was significantly lower in women who wake up earlier in the morning. All hormones except for cortisol had no significant correlation with PSQI global score in both groups and also the people who sleep less than 8 hours had lower cortisol level. These data showed that changes in cortisol in PCO women were due to damage of disturbed sleep at night. Our preliminary work provided this study with new insight into the interactions between sleep-wake cycles in PCO women with specific sleep patterns.
