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
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
Positron lifetime spectra have been measured in binary Ni Al alloys with different chemical composition and NiAl alloys doped with Cr, Zr, Fe and Mg. The results indicate that in B2 NiAl and Ll 2 Ni 3Al alloys, some o...Positron lifetime spectra have been measured in binary Ni Al alloys with different chemical composition and NiAl alloys doped with Cr, Zr, Fe and Mg. The results indicate that in B2 NiAl and Ll 2 Ni 3Al alloys, some of the valance electrons of Ni and Al atoms are localized, which leads to a lower free electron density of the alloy. The mean free electron density of the binary Ni Al alloy decreases with increasing Al content. The open volume of defects on grain boundary of the Ni 3Al is larger than that of monovacancy or dislocation. Structural vacancies and microvoids are found in B2 NiAl alloys with Al content above 45%(mole fraction), and the concentration of the vacancies and open volume of microvoids will increase with higher Al content. The addition of Cr, Zr and Fe into a NiAl alloy can increase its mean free electron density and reduce the open volume of defects on its grain boundary, while with addition of Mg into the NiAl alloy, its mean free electron density decreases and open volume of boundary defects increases.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
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.
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.
文摘Positron lifetime spectra have been measured in binary Ni Al alloys with different chemical composition and NiAl alloys doped with Cr, Zr, Fe and Mg. The results indicate that in B2 NiAl and Ll 2 Ni 3Al alloys, some of the valance electrons of Ni and Al atoms are localized, which leads to a lower free electron density of the alloy. The mean free electron density of the binary Ni Al alloy decreases with increasing Al content. The open volume of defects on grain boundary of the Ni 3Al is larger than that of monovacancy or dislocation. Structural vacancies and microvoids are found in B2 NiAl alloys with Al content above 45%(mole fraction), and the concentration of the vacancies and open volume of microvoids will increase with higher Al content. The addition of Cr, Zr and Fe into a NiAl alloy can increase its mean free electron density and reduce the open volume of defects on its grain boundary, while with addition of Mg into the NiAl alloy, its mean free electron density decreases and open volume of boundary defects increases.
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
