The presence of retained austenite gives rise to deterioration of the wear resistance and fracture strength of Cr-Mo steels in many cases. Thus, the effects of heat treatments including direct quenching, martempering,...The presence of retained austenite gives rise to deterioration of the wear resistance and fracture strength of Cr-Mo steels in many cases. Thus, the effects of heat treatments including direct quenching, martempering, and austempering on the retained austenite existing in the microstrueture of these steels were investigated. Specimens were austenized at 950 ℃ followed by direct quenching using compressed and still air. The specimens were also isothermally quenched in salt bath at 200 and 300 ℃ for 2, 8, 30, and 120min. Microstructures of the specimens were studied using optical microscope （traditional black and white etching as well as color etching）, scanning electron microscope （SEM）, microhardness tester, and X-ray diffraction （XRD）. The results showed that the lowest amount of retained austenite in the microstructure was obtained in the specimens quenched isothermally at 300 ℃ for 120 min.展开更多
This work discusses tribological properties of commercial pure (CP) titanium processed by multi-directional forging (MDF) up to six passes at room temperature and 220 ℃. For this purpose, wear test was conducted by d...This work discusses tribological properties of commercial pure (CP) titanium processed by multi-directional forging (MDF) up to six passes at room temperature and 220 ℃. For this purpose, wear test was conducted by dry sliding pin-on-disk method on the initial and ultrafine grained samples using different stress magnitudes of 1, 1.5 and 2 MPa. The results showed that wear resistance of CP titanium increases after the first pass of MDF in comparison with the initial condition, irrespective of the applied normal stress. For example, the average wear rate of MDFed samples was decreased about 30% and 24%, after first pass at room temperature and 220 ℃, respectively. However, average wear rate of the samples processed by six MDF passes was reduced about 40% at lower normal loads;it was increased about 9% at higher ones as compared to the initial condition. It was also found that the dominated wear mechanisms were abrasive and delaminated at the lower stresses, while the delamination mechanism was intensified and a slight adhesion was observed during the higher applied normal loads.展开更多
Bangladesh composes the most polluted air with Dhaka securing the top position. The purpose of the study is the enumeration of the prevalence of pathogenic bacteria in Dhaka city’s air and their antibiotic susceptibi...Bangladesh composes the most polluted air with Dhaka securing the top position. The purpose of the study is the enumeration of the prevalence of pathogenic bacteria in Dhaka city’s air and their antibiotic susceptibility to the common antibiotics. For the sample collection, different selective media was exposed in air where the highest and lowest CFU was 137 and 1 respectively. Pathogens were screened through Hemolysis, DNase and Coagulase test and identified by 16s rRNA sequencing followed by antibiotic susceptibility test. 16s rRNA sequencing revealed that the organisms were <em>Bacillus</em> <em>altitudinis</em> strain 41KF2bT.28, <em>Bacillus licheniformis</em> strain QMA46-2, <em>Bacillus altitudinis</em>, <em>Bacillus pumilis </em>strain BJ-DEBCR-34, <em>Staphylococcus aureus </em>strain TPS3156, <em>Bacillus sp </em>CO16, <em>Pseudomonas sp</em> strain 96LC22 and <em>Shigella dysenteriae</em> strain ATCC 13313. <em>Shigella dysenteriae</em>, <em>Staphylococcus aureus</em> were 81.81% and 54.54% resistant to the antibiotics. Whole-genome sequencing would help to observe mutations in the traits as changes in hemolytic activity were found during pathogenecity tests.展开更多
Purpose： Ocular trauma is the third leading cause of hospitalization in ophthalmology patients, imposing direct and indirect physical and psychological costs on society. This study aims to investigate the status of o...Purpose： Ocular trauma is the third leading cause of hospitalization in ophthalmology patients, imposing direct and indirect physical and psychological costs on society. This study aims to investigate the status of ocular trauma in hospitalized patients in the industrialized city of Kashan in 2011. Methods： This cross-sectional descriptive applied study was conducted in 2012 on patients hospitalized for ocular trauma. Data, including age, gender, occupation, education, timing of admission following accident, location of accident, type of injury, damaging instrument, and type of trauma, were collected using a questionnaire designed by a trained nurse, and analyzed using SPSS-lfi software by means of means _＋ standard deviation, frequency, and percentage for descriptive data and t-test, one-way analysis of variance, Chi-square and Fisher exact test for analysis at significance level ofp 〈 0.05. Results： In total, 82 patients were hospitalized due to ocular traumas. The majority of patients were male （65 patients, 79.3%）. Their mean age was （25.4 ± 21.4） years, with an age range of 20-40 years （30 patients, 36.6%）. Hyphema was the most common injury （26 patients, 25.5%）, home was the most frequent incident location （32 patients, 39%）, and knife or other cutting tools were mostly responsible for injuries （18 patients, 21.9%）. Patients were hospitalized for 1-6 days, and the average length of stay in hospital was 2.63 days. Frequency distribution of injuries based on whether or not ruptures differed significantly among different age groups. Conclusion： The majority of ocular trauma occurred in young males. Knife was the principle culprit for eye injuries, followed by vehicles. To reduce such incidents, it is recommended that people be trained to avoid high-risk behaviors when using knives and to better heed driving rules and regulations.展开更多
Equal channel angular pressing is an effective technique to control the texture and microstructure of metals and alloys. Texture and microstructure of an Al-7075 alloy subjected to repetitive equal channel angular pre...Equal channel angular pressing is an effective technique to control the texture and microstructure of metals and alloys. Texture and microstructure of an Al-7075 alloy subjected to repetitive equal channel angular pressing through a 90° die were evaluated by X-ray diffractometer and orientation imaging microscopy. It is observed that processing through different routes leads to different types of textures, in both qualitative and quantitative senses. The texture calculation by Labotex software reveals that texture strengthens after the first pass and weakens by progressing ECAP process up to 4 passes. Microstructure investigations show that after 4 passes of equal channel angular pressing via routes BC and A, very fine grains with average grain size of about 700 nm and 1 μm appear, respectively, and most of the grains evolve into arrays of high angle boundaries. The effects of covering the Al-7075 billets with copper tube on texture and microstructure were also studied.展开更多
The effect of friction stir processing(FSP)at different rotation speeds(400,630,800,and 1000 r/min)and traverse speeds(25 and 50 mm/min)on the tribological properties of a Si particle reinforced Zn−40Al−2Cu-based in-s...The effect of friction stir processing(FSP)at different rotation speeds(400,630,800,and 1000 r/min)and traverse speeds(25 and 50 mm/min)on the tribological properties of a Si particle reinforced Zn−40Al−2Cu-based in-situ composite was investigated.After preliminary optimization,800 r/min and 25 mm/min were selected as optimum FSP parameters.According to the results,multi-pass FSP improved the tribological properties.For instance,at an applied pressure of 0.75 MPa,the wear rate and average coefficient of friction(COF)of four-pass FSPed composite were lower than those of base composite by 53%and 50%,respectively.SEM examinations of worn surfaces,wear debris,and worn subsurfaces revealed that the intensive refinement and uniform distribution of microstructural phases,especially the coarse Si particles,reduced Si particles interspacing,and elimination of casting defects were the most important factors enhancing the substrate resistance against sliding-induced deformation.This led to the formation of stable tribolayers that improved the tribological properties.展开更多
The microstructure,diffusional and mechanical bonding behavior and microhardness distribution of laminated composites fabricated by ECAP process were investigated.Al?Cu and Cu?Ni laminated composites were produced by ...The microstructure,diffusional and mechanical bonding behavior and microhardness distribution of laminated composites fabricated by ECAP process were investigated.Al?Cu and Cu?Ni laminated composites were produced by ECAP process up to4passes at room temperature and high temperature(300°C).The results of microstructure characterization by SEM and shear strength test revealed that the joints between the layers of4-pass ECAPed samples were considerably stronger than those of1-pass ECAPed samples due to tolerating higher values of plastic deformations during ECAP.Furthermore,shear strength data showed that increasing ECAP temperature caused a notable increase in shear strength of the specimens.The reason lies in the formation of diffusional joint between the interface of both Al/Cu and Cu/Ni layers at high temperature.The shear bonding strength of ECAPed Cu/Ni/Cu composite at high temperature was remarkably higher than that of ECAPed Cu/Al/Cu composite.展开更多
文摘The presence of retained austenite gives rise to deterioration of the wear resistance and fracture strength of Cr-Mo steels in many cases. Thus, the effects of heat treatments including direct quenching, martempering, and austempering on the retained austenite existing in the microstrueture of these steels were investigated. Specimens were austenized at 950 ℃ followed by direct quenching using compressed and still air. The specimens were also isothermally quenched in salt bath at 200 and 300 ℃ for 2, 8, 30, and 120min. Microstructures of the specimens were studied using optical microscope （traditional black and white etching as well as color etching）, scanning electron microscope （SEM）, microhardness tester, and X-ray diffraction （XRD）. The results showed that the lowest amount of retained austenite in the microstructure was obtained in the specimens quenched isothermally at 300 ℃ for 120 min.
基金supported financially by the Iran National Science Foundation (No.94809610)the Czech Science Foundation Project (No.GB 14-36566G)
文摘This work discusses tribological properties of commercial pure (CP) titanium processed by multi-directional forging (MDF) up to six passes at room temperature and 220 ℃. For this purpose, wear test was conducted by dry sliding pin-on-disk method on the initial and ultrafine grained samples using different stress magnitudes of 1, 1.5 and 2 MPa. The results showed that wear resistance of CP titanium increases after the first pass of MDF in comparison with the initial condition, irrespective of the applied normal stress. For example, the average wear rate of MDFed samples was decreased about 30% and 24%, after first pass at room temperature and 220 ℃, respectively. However, average wear rate of the samples processed by six MDF passes was reduced about 40% at lower normal loads;it was increased about 9% at higher ones as compared to the initial condition. It was also found that the dominated wear mechanisms were abrasive and delaminated at the lower stresses, while the delamination mechanism was intensified and a slight adhesion was observed during the higher applied normal loads.
文摘Bangladesh composes the most polluted air with Dhaka securing the top position. The purpose of the study is the enumeration of the prevalence of pathogenic bacteria in Dhaka city’s air and their antibiotic susceptibility to the common antibiotics. For the sample collection, different selective media was exposed in air where the highest and lowest CFU was 137 and 1 respectively. Pathogens were screened through Hemolysis, DNase and Coagulase test and identified by 16s rRNA sequencing followed by antibiotic susceptibility test. 16s rRNA sequencing revealed that the organisms were <em>Bacillus</em> <em>altitudinis</em> strain 41KF2bT.28, <em>Bacillus licheniformis</em> strain QMA46-2, <em>Bacillus altitudinis</em>, <em>Bacillus pumilis </em>strain BJ-DEBCR-34, <em>Staphylococcus aureus </em>strain TPS3156, <em>Bacillus sp </em>CO16, <em>Pseudomonas sp</em> strain 96LC22 and <em>Shigella dysenteriae</em> strain ATCC 13313. <em>Shigella dysenteriae</em>, <em>Staphylococcus aureus</em> were 81.81% and 54.54% resistant to the antibiotics. Whole-genome sequencing would help to observe mutations in the traits as changes in hemolytic activity were found during pathogenecity tests.
文摘Purpose： Ocular trauma is the third leading cause of hospitalization in ophthalmology patients, imposing direct and indirect physical and psychological costs on society. This study aims to investigate the status of ocular trauma in hospitalized patients in the industrialized city of Kashan in 2011. Methods： This cross-sectional descriptive applied study was conducted in 2012 on patients hospitalized for ocular trauma. Data, including age, gender, occupation, education, timing of admission following accident, location of accident, type of injury, damaging instrument, and type of trauma, were collected using a questionnaire designed by a trained nurse, and analyzed using SPSS-lfi software by means of means _＋ standard deviation, frequency, and percentage for descriptive data and t-test, one-way analysis of variance, Chi-square and Fisher exact test for analysis at significance level ofp 〈 0.05. Results： In total, 82 patients were hospitalized due to ocular traumas. The majority of patients were male （65 patients, 79.3%）. Their mean age was （25.4 ± 21.4） years, with an age range of 20-40 years （30 patients, 36.6%）. Hyphema was the most common injury （26 patients, 25.5%）, home was the most frequent incident location （32 patients, 39%）, and knife or other cutting tools were mostly responsible for injuries （18 patients, 21.9%）. Patients were hospitalized for 1-6 days, and the average length of stay in hospital was 2.63 days. Frequency distribution of injuries based on whether or not ruptures differed significantly among different age groups. Conclusion： The majority of ocular trauma occurred in young males. Knife was the principle culprit for eye injuries, followed by vehicles. To reduce such incidents, it is recommended that people be trained to avoid high-risk behaviors when using knives and to better heed driving rules and regulations.
文摘Equal channel angular pressing is an effective technique to control the texture and microstructure of metals and alloys. Texture and microstructure of an Al-7075 alloy subjected to repetitive equal channel angular pressing through a 90° die were evaluated by X-ray diffractometer and orientation imaging microscopy. It is observed that processing through different routes leads to different types of textures, in both qualitative and quantitative senses. The texture calculation by Labotex software reveals that texture strengthens after the first pass and weakens by progressing ECAP process up to 4 passes. Microstructure investigations show that after 4 passes of equal channel angular pressing via routes BC and A, very fine grains with average grain size of about 700 nm and 1 μm appear, respectively, and most of the grains evolve into arrays of high angle boundaries. The effects of covering the Al-7075 billets with copper tube on texture and microstructure were also studied.
文摘The effect of friction stir processing(FSP)at different rotation speeds(400,630,800,and 1000 r/min)and traverse speeds(25 and 50 mm/min)on the tribological properties of a Si particle reinforced Zn−40Al−2Cu-based in-situ composite was investigated.After preliminary optimization,800 r/min and 25 mm/min were selected as optimum FSP parameters.According to the results,multi-pass FSP improved the tribological properties.For instance,at an applied pressure of 0.75 MPa,the wear rate and average coefficient of friction(COF)of four-pass FSPed composite were lower than those of base composite by 53%and 50%,respectively.SEM examinations of worn surfaces,wear debris,and worn subsurfaces revealed that the intensive refinement and uniform distribution of microstructural phases,especially the coarse Si particles,reduced Si particles interspacing,and elimination of casting defects were the most important factors enhancing the substrate resistance against sliding-induced deformation.This led to the formation of stable tribolayers that improved the tribological properties.
文摘The microstructure,diffusional and mechanical bonding behavior and microhardness distribution of laminated composites fabricated by ECAP process were investigated.Al?Cu and Cu?Ni laminated composites were produced by ECAP process up to4passes at room temperature and high temperature(300°C).The results of microstructure characterization by SEM and shear strength test revealed that the joints between the layers of4-pass ECAPed samples were considerably stronger than those of1-pass ECAPed samples due to tolerating higher values of plastic deformations during ECAP.Furthermore,shear strength data showed that increasing ECAP temperature caused a notable increase in shear strength of the specimens.The reason lies in the formation of diffusional joint between the interface of both Al/Cu and Cu/Ni layers at high temperature.The shear bonding strength of ECAPed Cu/Ni/Cu composite at high temperature was remarkably higher than that of ECAPed Cu/Al/Cu composite.
