As a virtual experimental device for analysis and calculation of grown-in microdefects formation in undoped silicon dislocation-free single crystals the software is proposed. The software is built on the basis on diff...As a virtual experimental device for analysis and calculation of grown-in microdefects formation in undoped silicon dislocation-free single crystals the software is proposed. The software is built on the basis on diffusion model of formation, growth and coalescence of grown-in microdefects. Diffusion model describes kinetics of defect structure changes during cooling after growth on crystallization temperature to room temperature. The software allows the use of personal computer to investigate the defect structure of dislocation-free silicon single crystals with a diameter on 30 mm to 400 mm grown by floating-zone and Czochralski methods.展开更多
The microdefects and free electron densities in B2,R and B19’ phases of Ni50.78Ti49.22 alloy were studied by positron lifetime measurements.Comparing the lifetime parameters of the Ni50.78Ti49.22 alloy measured at 29...The microdefects and free electron densities in B2,R and B19’ phases of Ni50.78Ti49.22 alloy were studied by positron lifetime measurements.Comparing the lifetime parameters of the Ni50.78Ti49.22 alloy measured at 295 K and 225 K,it is found that the free electron density of the R phase is lower than that of the B2 phase;the open volume of the defects of the R phase is larger,while the concentration of these defects is lower than that of the B2 phase.The Ni50.78Ti49.22 alloy exhibits B19’ phase at 115 K.In comparison with the R phase,the free electron density of the B19’ phase increases,the open volume of the defects of the B19’ phase reduces,and the concentration of these defects increases.The microdefects and the free electron density play an important role during the multi-step transformations(B2→R→B19’ phase transformations)in Ni50.78Ti49.22 alloy with the decrease of temperature.展开更多
The long-range ordered intermetallic compounds FeAl alloys with B2 crystalstructure are characterized by superior high-temperature strength, excellent oxidation re-sistance, low density and low cost, so that they are ...The long-range ordered intermetallic compounds FeAl alloys with B2 crystalstructure are characterized by superior high-temperature strength, excellent oxidation re-sistance, low density and low cost, so that they are available for the futurehigh-emperature structure materials. But the room temperature brittleness of FeAl al-loys has been the major obstacle for its engineering applications. The binary FeAl withmore than 40 at.% Al content showed mainly intergranular fracture. The cohesions展开更多
Cemented carbide tools are widely utilized in titanium alloy machining.However,severe tool wear usually occurs during machining;thus,the wear process has attracted widespread attention.Electromagnetic treatment was ap...Cemented carbide tools are widely utilized in titanium alloy machining.However,severe tool wear usually occurs during machining;thus,the wear process has attracted widespread attention.Electromagnetic treatment was applied in our previous study to significantly improve the tool life of cemented carbide tools in Ti6Al4V machining.To investigate the effect of electromagnetic treatment on wear performance,a multiscale analysis of the wear process of cemented carbide tools in the turning process,including microdefects and wear topography at various scales,was conducted in the present study.The distribution of dislocations in the tool material was measured through electron backscatter diffraction,and the surface topographies in the wear area during the Ti6Al4V cutting process were recorded via white light interferometry.Fractal analysis based on the scaling property of surface roughness was carried out to further quantify the wear performance of the tools.The results revealed that the wear mechanism of the cutting tools was mainly adhesion and diffusion,and the diffusion wear of the electromagnetically treated tools was less than that of the untreated tools.Based on the multiscale analysis of flank wear,the effect of electromagnetic treatment on the enhancement of the wear resistance of cemented carbide cutting tools was demonstrated.The multiscale analysis of the wear performance of cutting tools in this study effectively revealed the mechanism by which electromagnetic treatment enhances wear resistance,thus contributing to filling the research gap of traditional studies on tool wear that generally employ single scales.展开更多
NiAl alloy is considered to be a good candidate material for high performance, high-tempera-ture structural applications since this material offers a wide range of attractive mechanical andphysical properties, such as...NiAl alloy is considered to be a good candidate material for high performance, high-tempera-ture structural applications since this material offers a wide range of attractive mechanical andphysical properties, such as low density (5. 86 g/cm^3), high melting point (1 640℃), goodthermal conductivity (4--8 times compared with Ni-based superalloys) and oxidation resis-tance. However, the use of NiAl is limited by its room-temperature brittleness. Georgeand Liu have investigated the effects of microalloying elements B, C and Be on the fractureproperties and grain boundaries of NiAl alloy. Their results showed that the improvement展开更多
Positron lifetime measurements have been performed in binary Fe3Al and Fe3Al doping with Nb or Si alloys. The densities of valence electrons of the bulk and microdefects in all tested samples have been calculated by u...Positron lifetime measurements have been performed in binary Fe3Al and Fe3Al doping with Nb or Si alloys. The densities of valence electrons of the bulk and microdefects in all tested samples have been calculated by using the positron lifetime parameters. Density of valence electron is low in the bulk of Fe3Al alloy. It indicates that, the 3d electrons in a Fe atom have strong-localized properties and tend to form covalent bonds with Al atoms, and the bonding nature in Fe3Al is a mixture of metallic and covalent bonds. The density of valence electron is very low in the defects of Fe3Al grain boundary, which makes the bonding cohesion in grain boundary quite weak. The addition of Si to Fe3Al gives rise to the decrease of the densities of valence electrons in the bulk and the grain boundary thus the metallic bonding cohesion. This makes the alloy more brittle. The addition of Nb to Fe3Al results in the decrease of the ordering energy of the alloy and increases the density of valence electron and the bonding cohesion of the grain boundary. However, since the radius of Nb atom is larger than that of Fe atom, when Nb atoms substitute for Fe atoms, they will distort the lattice and enlarge the volume of the lattice, which decreases the density of valence electron and the cohesion of metallic bond in the bulk of the alloy.展开更多
文摘As a virtual experimental device for analysis and calculation of grown-in microdefects formation in undoped silicon dislocation-free single crystals the software is proposed. The software is built on the basis on diffusion model of formation, growth and coalescence of grown-in microdefects. Diffusion model describes kinetics of defect structure changes during cooling after growth on crystallization temperature to room temperature. The software allows the use of personal computer to investigate the defect structure of dislocation-free silicon single crystals with a diameter on 30 mm to 400 mm grown by floating-zone and Czochralski methods.
基金Project(50361002) supported by the National Natural Science Foundations of ChinaProject(0448006) supported by the Natural Science Foundation of Guangxi Province,China
文摘The microdefects and free electron densities in B2,R and B19’ phases of Ni50.78Ti49.22 alloy were studied by positron lifetime measurements.Comparing the lifetime parameters of the Ni50.78Ti49.22 alloy measured at 295 K and 225 K,it is found that the free electron density of the R phase is lower than that of the B2 phase;the open volume of the defects of the R phase is larger,while the concentration of these defects is lower than that of the B2 phase.The Ni50.78Ti49.22 alloy exhibits B19’ phase at 115 K.In comparison with the R phase,the free electron density of the B19’ phase increases,the open volume of the defects of the B19’ phase reduces,and the concentration of these defects increases.The microdefects and the free electron density play an important role during the multi-step transformations(B2→R→B19’ phase transformations)in Ni50.78Ti49.22 alloy with the decrease of temperature.
基金Project supported by the National Natural Science Foundation of China.
文摘The long-range ordered intermetallic compounds FeAl alloys with B2 crystalstructure are characterized by superior high-temperature strength, excellent oxidation re-sistance, low density and low cost, so that they are available for the futurehigh-emperature structure materials. But the room temperature brittleness of FeAl al-loys has been the major obstacle for its engineering applications. The binary FeAl withmore than 40 at.% Al content showed mainly intergranular fracture. The cohesions
基金supported by the National Natural Science Foundation of China(No.52275441)the Shenzhen Science and Technology Program(No.KJZD20230923114606013).
文摘Cemented carbide tools are widely utilized in titanium alloy machining.However,severe tool wear usually occurs during machining;thus,the wear process has attracted widespread attention.Electromagnetic treatment was applied in our previous study to significantly improve the tool life of cemented carbide tools in Ti6Al4V machining.To investigate the effect of electromagnetic treatment on wear performance,a multiscale analysis of the wear process of cemented carbide tools in the turning process,including microdefects and wear topography at various scales,was conducted in the present study.The distribution of dislocations in the tool material was measured through electron backscatter diffraction,and the surface topographies in the wear area during the Ti6Al4V cutting process were recorded via white light interferometry.Fractal analysis based on the scaling property of surface roughness was carried out to further quantify the wear performance of the tools.The results revealed that the wear mechanism of the cutting tools was mainly adhesion and diffusion,and the diffusion wear of the electromagnetically treated tools was less than that of the untreated tools.Based on the multiscale analysis of flank wear,the effect of electromagnetic treatment on the enhancement of the wear resistance of cemented carbide cutting tools was demonstrated.The multiscale analysis of the wear performance of cutting tools in this study effectively revealed the mechanism by which electromagnetic treatment enhances wear resistance,thus contributing to filling the research gap of traditional studies on tool wear that generally employ single scales.
文摘NiAl alloy is considered to be a good candidate material for high performance, high-tempera-ture structural applications since this material offers a wide range of attractive mechanical andphysical properties, such as low density (5. 86 g/cm^3), high melting point (1 640℃), goodthermal conductivity (4--8 times compared with Ni-based superalloys) and oxidation resis-tance. However, the use of NiAl is limited by its room-temperature brittleness. Georgeand Liu have investigated the effects of microalloying elements B, C and Be on the fractureproperties and grain boundaries of NiAl alloy. Their results showed that the improvement
基金Project supported by the National Natural Science Foundation of China (Grant No. 59561001)the Foundation of Guangxi Education Committee
文摘Positron lifetime measurements have been performed in binary Fe3Al and Fe3Al doping with Nb or Si alloys. The densities of valence electrons of the bulk and microdefects in all tested samples have been calculated by using the positron lifetime parameters. Density of valence electron is low in the bulk of Fe3Al alloy. It indicates that, the 3d electrons in a Fe atom have strong-localized properties and tend to form covalent bonds with Al atoms, and the bonding nature in Fe3Al is a mixture of metallic and covalent bonds. The density of valence electron is very low in the defects of Fe3Al grain boundary, which makes the bonding cohesion in grain boundary quite weak. The addition of Si to Fe3Al gives rise to the decrease of the densities of valence electrons in the bulk and the grain boundary thus the metallic bonding cohesion. This makes the alloy more brittle. The addition of Nb to Fe3Al results in the decrease of the ordering energy of the alloy and increases the density of valence electron and the bonding cohesion of the grain boundary. However, since the radius of Nb atom is larger than that of Fe atom, when Nb atoms substitute for Fe atoms, they will distort the lattice and enlarge the volume of the lattice, which decreases the density of valence electron and the cohesion of metallic bond in the bulk of the alloy.
