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 oxidation behaviors of two kinds of low segregation Ht-Cr-Al based superalloys have been studied between 1000-1100℃, and compared with that of general Mt-Cr-Al based superalloys. The results indicated that the si...The oxidation behaviors of two kinds of low segregation Ht-Cr-Al based superalloys have been studied between 1000-1100℃, and compared with that of general Mt-Cr-Al based superalloys. The results indicated that the simultaneous additions of 0.1 wt% S and 0. 1 wt% Zr to low segregation alloys increase the oxidation rate of Al2O3-forming alloy and improve the scale adherence. The addition of 0.1 wt% Zr can ,minimize the negative effects of S on the adherence of Al2O3 scale. Low amounts of S(≤50 ppm wt) have no obviously negative effects on the adherence of Cr2O3 scale formed on one of the low segregation superalloys.展开更多
The surface segregation of substrate elements through the Au layer in the Au-Ni-Kovar sys- tem specimens heated at 250—350℃ for 0.5—1.5 h has been studied by SAM and XPS. Visual evidence of the mechanism for Ni and...The surface segregation of substrate elements through the Au layer in the Au-Ni-Kovar sys- tem specimens heated at 250—350℃ for 0.5—1.5 h has been studied by SAM and XPS. Visual evidence of the mechanism for Ni and Co surface segregation of the complicated sys- tem has been given,i.e.Ni and Co penetrated the gold layer mainly by grain boundary diffu- sion and then covered the Au layer by surface diffusion.The strdy results of the chemical states of surface segregation elements not only indicate that oxygen adsorption and oxidation reaction are the driving force for the surface segregation of Ni and Co,but also show that the above segregation can result in water absorption on surfaces.展开更多
Interaction rule between representative RE and Sn, Sb, Pb, Cu, S, P low melting point elements respectively in Fe , Cu , Al , Ni base liquid solutions including totally 34 ternary and quarternary systems was inve...Interaction rule between representative RE and Sn, Sb, Pb, Cu, S, P low melting point elements respectively in Fe , Cu , Al , Ni base liquid solutions including totally 34 ternary and quarternary systems was investigated. For each system some thermodynamic properties were obtained, such as the standard free energies of equilibrium reactions, activity interaction coefficients etc ..展开更多
Composite nickel hydroxide films were prepared by cathodic co electrodeposition from metal nitrate solution and characterized by cyclic voltammetry in 1.0 mol/L KOH solution. The codeposited light rare earth elements...Composite nickel hydroxide films were prepared by cathodic co electrodeposition from metal nitrate solution and characterized by cyclic voltammetry in 1.0 mol/L KOH solution. The codeposited light rare earth elements were lanthanum, cerium, praseodymium and neodymium. The films were analyzed by spectrophotometry and optical transmission. The results of the cyclic voltammetry in 1.0 mol/L KOH solution showed that the current density for oxygen evolution at the film electrode was affected by the co deposited rare earth metal ions in the film. About 20 mA/cm 2 increase of current density for oxygen evolution was found when the film was obtained from the solution with cerium (7% v/v) and nickel (93% v/v) nitrate. The effects of galvanostatic cathodic current density for the film formation on the oxygen evolution at the film electrodes from the alkaline were discussed.展开更多
The finite element method was applied to study the mechanics of rafting ofγ' precipitates in a single crystal Ni-based superalloy with the [001] orientation. The results show that the creep and rafting are closel...The finite element method was applied to study the mechanics of rafting ofγ' precipitates in a single crystal Ni-based superalloy with the [001] orientation. The results show that the creep and rafting are closely related with the stress and strain energy density distributions in the matrix channels. The application of an external stress leads to differential levels of von Mises stress and strain energy density, and the largest value of the stress appears at the corners of the matrix near the interface. Creep dislocations penetrate preferentially into the most highly stressed matrix channels where theγ'-phase rafting is also enlarged. Meanwhile, the von Mises stress ofγmatrix andγ' precipitate increases with the increase of temperature, thus the rafting becomes easier at a higher temperature. Moreover, according to the analysis of slip systems for the Ni-based superalloy, the critical external load for bowing a dislocation through a matrix channel at 950℃is about 180 MPa, which is consistent with the related experimental results.展开更多
Among the various grades of commercially available 18 wt. % nickel maraging steels, the one with nominal 0.2% proof strength in the range 1700-1750 MPa is the most commonly used and is distinguished by an excellent co...Among the various grades of commercially available 18 wt. % nickel maraging steels, the one with nominal 0.2% proof strength in the range 1700-1750 MPa is the most commonly used and is distinguished by an excellent combination of high strength and high fracture toughness. The main alloying elements are nickel, cobalt, molybdenum and titanium. The first three of these are present at relatively high concentrations in the chemical composition. The high cost of these metals leads to a high cost of production and this becomes a deterrent to extensive use of the steel. In the present study, an attempt was made to produce the steel by pegging the levels of these alloying elements in the lower half of the specified range. The objective was to save on the raw material cost, while still conforming to the specification. The steel so produced could not, however, attain the specified tensile properties after final heat treatment. The observed behavior is explained based on the role played by the different alloying elements in driving the precipitation hardening reaction.展开更多
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.
文摘The oxidation behaviors of two kinds of low segregation Ht-Cr-Al based superalloys have been studied between 1000-1100℃, and compared with that of general Mt-Cr-Al based superalloys. The results indicated that the simultaneous additions of 0.1 wt% S and 0. 1 wt% Zr to low segregation alloys increase the oxidation rate of Al2O3-forming alloy and improve the scale adherence. The addition of 0.1 wt% Zr can ,minimize the negative effects of S on the adherence of Al2O3 scale. Low amounts of S(≤50 ppm wt) have no obviously negative effects on the adherence of Cr2O3 scale formed on one of the low segregation superalloys.
文摘The surface segregation of substrate elements through the Au layer in the Au-Ni-Kovar sys- tem specimens heated at 250—350℃ for 0.5—1.5 h has been studied by SAM and XPS. Visual evidence of the mechanism for Ni and Co surface segregation of the complicated sys- tem has been given,i.e.Ni and Co penetrated the gold layer mainly by grain boundary diffu- sion and then covered the Au layer by surface diffusion.The strdy results of the chemical states of surface segregation elements not only indicate that oxygen adsorption and oxidation reaction are the driving force for the surface segregation of Ni and Co,but also show that the above segregation can result in water absorption on surfaces.
基金Project Sponsored by the National Natural Science Foundation
文摘Interaction rule between representative RE and Sn, Sb, Pb, Cu, S, P low melting point elements respectively in Fe , Cu , Al , Ni base liquid solutions including totally 34 ternary and quarternary systems was investigated. For each system some thermodynamic properties were obtained, such as the standard free energies of equilibrium reactions, activity interaction coefficients etc ..
文摘Composite nickel hydroxide films were prepared by cathodic co electrodeposition from metal nitrate solution and characterized by cyclic voltammetry in 1.0 mol/L KOH solution. The codeposited light rare earth elements were lanthanum, cerium, praseodymium and neodymium. The films were analyzed by spectrophotometry and optical transmission. The results of the cyclic voltammetry in 1.0 mol/L KOH solution showed that the current density for oxygen evolution at the film electrode was affected by the co deposited rare earth metal ions in the film. About 20 mA/cm 2 increase of current density for oxygen evolution was found when the film was obtained from the solution with cerium (7% v/v) and nickel (93% v/v) nitrate. The effects of galvanostatic cathodic current density for the film formation on the oxygen evolution at the film electrodes from the alkaline were discussed.
基金Projects(10572019, 10672016)supported by the National Natural Science Foundation of Chinaproject(2005SM0035) supported by the Science Foundation of Beijing Jiaotong University, China
文摘The finite element method was applied to study the mechanics of rafting ofγ' precipitates in a single crystal Ni-based superalloy with the [001] orientation. The results show that the creep and rafting are closely related with the stress and strain energy density distributions in the matrix channels. The application of an external stress leads to differential levels of von Mises stress and strain energy density, and the largest value of the stress appears at the corners of the matrix near the interface. Creep dislocations penetrate preferentially into the most highly stressed matrix channels where theγ'-phase rafting is also enlarged. Meanwhile, the von Mises stress ofγmatrix andγ' precipitate increases with the increase of temperature, thus the rafting becomes easier at a higher temperature. Moreover, according to the analysis of slip systems for the Ni-based superalloy, the critical external load for bowing a dislocation through a matrix channel at 950℃is about 180 MPa, which is consistent with the related experimental results.
文摘Among the various grades of commercially available 18 wt. % nickel maraging steels, the one with nominal 0.2% proof strength in the range 1700-1750 MPa is the most commonly used and is distinguished by an excellent combination of high strength and high fracture toughness. The main alloying elements are nickel, cobalt, molybdenum and titanium. The first three of these are present at relatively high concentrations in the chemical composition. The high cost of these metals leads to a high cost of production and this becomes a deterrent to extensive use of the steel. In the present study, an attempt was made to produce the steel by pegging the levels of these alloying elements in the lower half of the specified range. The objective was to save on the raw material cost, while still conforming to the specification. The steel so produced could not, however, attain the specified tensile properties after final heat treatment. The observed behavior is explained based on the role played by the different alloying elements in driving the precipitation hardening reaction.
