This study systematically investigated the microstructure,mechanical properties,and corrosion behavior of an extruded Zn-0.2Mg alloy processed by multi-directional forging(MDF)at 100℃.The mean grain size was remarkab...This study systematically investigated the microstructure,mechanical properties,and corrosion behavior of an extruded Zn-0.2Mg alloy processed by multi-directional forging(MDF)at 100℃.The mean grain size was remarkably decreased from 17.2±0.5µm to 1.9±0.3µm,and 84.4%of the microstructure was occupied by grains of below 1µm in size after applying three MDF passes.Electron backscattered difraction examinations revealed that continuous dynamic recrystallization,progressive lattice rotation,and particle-stimulated nucleation mechanisms were recognized as contributing to microstructural evolution.Furthermore,transmission electron microscopy results showed that nanoparticles of Mg/Zn dynamically formed under high strain MDF,while the initial extrusion fber texture was altered to be<0001>parallel to the fnal forging axis.A synergistic efect of grain refnement,texture evolution,second-phase precipitates,and dislocation strengthening resulted in an increased ultimate tensile strength of 232±5 MPa after three MDF passes.However,this was accompanied by a reduction in the elongation(8±2.1%).Additionally,a high corrosion rate of 0.59 mm/year was measured for the experimental alloy fabricated by 3 MDF passes.In agreement with the latter,electrochemical impedance spectroscopy results indicated that the grain refnement improved the passivation kinetics of the oxide layer.展开更多
Aluminum and silver strips were cold welded by rolling and a bimetallic strip was produced. To create cold weld between A1 and Ag, mating surfaces were specially prepared and various rolling thickness reductions were ...Aluminum and silver strips were cold welded by rolling and a bimetallic strip was produced. To create cold weld between A1 and Ag, mating surfaces were specially prepared and various rolling thickness reductions were applied. The minimum critical thickness reduction to begin cold weld was specified as 70% which equals 0.1630 critical rolling shape factors. The bimetallic strips were treated by diffusion annealing at 400 ~C and various annealing time. The A1/Ag interface of strips was observed by scanning electron microscope to investigate the formation of hard and brittle probable phases. The effect of anneal time on diffusion distance and phase transformation was also analysed by EDS analysis and line scan. A diffusion region along the interface in the Ag side was observed and its width increased with prolonging annealing time. Some 8 phases were detected close to the interface after anneal treating for 3 h and 8 phase was thicker and more continuous by increasing annealing time. The microhardness measurement showed that in spite of formation of 8 phase due to diffusion annealing, the interface hardness was reduced.展开更多
Background: Pulp stones are calcified masses formed in the primary and permanent dentitions. The ischemic cardiovascular disorders (CVD) can be the first health problem of the world. It seems that there is a relations...Background: Pulp stones are calcified masses formed in the primary and permanent dentitions. The ischemic cardiovascular disorders (CVD) can be the first health problem of the world. It seems that there is a relationship between pulp stones and cardiovascular diseases to determine the diagnostic value of panoramic dental radiographs as non-invasive test for the early detection of CVD. Methods and Materials: The subjects of the study came from patients presenting to Dental Radiology Department of Dental School in Yazd who aged 30 - 64 years, had 8 natural teeth. They were referred to the Cardiovascular Center of Afshar Hospital in Yazd for cardiovascular evaluation. To set the cut-off point, the ratio of teeth with pulp stones to the total number of teeth for each person was calculated and also ABI for diagnosing IHD via ROC curve was used. Results: Only 3.8% of patients without pulp stone were affected by ischemic heart disease (IHD). About Sixty seven percent (67.3%) of individuals had at least one tooth with pulp stone. In individuals without IHD, 5% of the teeth showed pulp stone while this rate was 45% (9 times) in CVD patients. The number of patients for whom the ratio of teeth with pulp stone to total number of teeth was 0.2 or more, was 138.7 times greater than the other. Conclusion: The dentists, who order panoramic radiographs for the treatment of patients, exactly study those teeth for the presence of pulp stones. The ratio of teeth with pulp stone to total teeth equal 0.2 or more was a good tool for early detection of CVD.展开更多
文摘This study systematically investigated the microstructure,mechanical properties,and corrosion behavior of an extruded Zn-0.2Mg alloy processed by multi-directional forging(MDF)at 100℃.The mean grain size was remarkably decreased from 17.2±0.5µm to 1.9±0.3µm,and 84.4%of the microstructure was occupied by grains of below 1µm in size after applying three MDF passes.Electron backscattered difraction examinations revealed that continuous dynamic recrystallization,progressive lattice rotation,and particle-stimulated nucleation mechanisms were recognized as contributing to microstructural evolution.Furthermore,transmission electron microscopy results showed that nanoparticles of Mg/Zn dynamically formed under high strain MDF,while the initial extrusion fber texture was altered to be<0001>parallel to the fnal forging axis.A synergistic efect of grain refnement,texture evolution,second-phase precipitates,and dislocation strengthening resulted in an increased ultimate tensile strength of 232±5 MPa after three MDF passes.However,this was accompanied by a reduction in the elongation(8±2.1%).Additionally,a high corrosion rate of 0.59 mm/year was measured for the experimental alloy fabricated by 3 MDF passes.In agreement with the latter,electrochemical impedance spectroscopy results indicated that the grain refnement improved the passivation kinetics of the oxide layer.
文摘Aluminum and silver strips were cold welded by rolling and a bimetallic strip was produced. To create cold weld between A1 and Ag, mating surfaces were specially prepared and various rolling thickness reductions were applied. The minimum critical thickness reduction to begin cold weld was specified as 70% which equals 0.1630 critical rolling shape factors. The bimetallic strips were treated by diffusion annealing at 400 ~C and various annealing time. The A1/Ag interface of strips was observed by scanning electron microscope to investigate the formation of hard and brittle probable phases. The effect of anneal time on diffusion distance and phase transformation was also analysed by EDS analysis and line scan. A diffusion region along the interface in the Ag side was observed and its width increased with prolonging annealing time. Some 8 phases were detected close to the interface after anneal treating for 3 h and 8 phase was thicker and more continuous by increasing annealing time. The microhardness measurement showed that in spite of formation of 8 phase due to diffusion annealing, the interface hardness was reduced.
文摘Background: Pulp stones are calcified masses formed in the primary and permanent dentitions. The ischemic cardiovascular disorders (CVD) can be the first health problem of the world. It seems that there is a relationship between pulp stones and cardiovascular diseases to determine the diagnostic value of panoramic dental radiographs as non-invasive test for the early detection of CVD. Methods and Materials: The subjects of the study came from patients presenting to Dental Radiology Department of Dental School in Yazd who aged 30 - 64 years, had 8 natural teeth. They were referred to the Cardiovascular Center of Afshar Hospital in Yazd for cardiovascular evaluation. To set the cut-off point, the ratio of teeth with pulp stones to the total number of teeth for each person was calculated and also ABI for diagnosing IHD via ROC curve was used. Results: Only 3.8% of patients without pulp stone were affected by ischemic heart disease (IHD). About Sixty seven percent (67.3%) of individuals had at least one tooth with pulp stone. In individuals without IHD, 5% of the teeth showed pulp stone while this rate was 45% (9 times) in CVD patients. The number of patients for whom the ratio of teeth with pulp stone to total number of teeth was 0.2 or more, was 138.7 times greater than the other. Conclusion: The dentists, who order panoramic radiographs for the treatment of patients, exactly study those teeth for the presence of pulp stones. The ratio of teeth with pulp stone to total teeth equal 0.2 or more was a good tool for early detection of CVD.
