In this study, the electrochemical reduction of Y(Ⅲ)on nickel electrode has been investigated. The resultsshow that there are several plateaus for formation of intermetallic compounds preceding reduction peak ofyttri...In this study, the electrochemical reduction of Y(Ⅲ)on nickel electrode has been investigated. The resultsshow that there are several plateaus for formation of intermetallic compounds preceding reduction peak ofyttrium. A linear relationship between the current and t￣(-1/2) has been obtained, showing that Cottrell's law isobeyed.展开更多
Fibrous particulate precursor was obtained by precipitation transformation in the ternary solution system of ammonium oxalate, nickel chloride and ammonia. The composition and morphology of precursor were characterize...Fibrous particulate precursor was obtained by precipitation transformation in the ternary solution system of ammonium oxalate, nickel chloride and ammonia. The composition and morphology of precursor were characterized by XRD, SEM, IR and DTA/TGA analyses. The results show that the chemical composition and morphology of precursor precipitates at pH=8.4？8.8 are different from those of precursor precipitates at pH=6.0, and the mechanisms of the thermal decomposition of the precursors are different. The effects of various conditions in the process of thermal decomposition, including precursor morphology, atmosphere, temperature and time on the morphology and dispersion degree of obtained nickel powders were studied in detail. The final product inherits the morphology of precursor when the thermal decomposition is conducted under a weakly reducing atmosphere at temperature range of 400？440 °C for 30 min. Fibrous nickel powder can be produced with good dispersion, and its shape changes from smooth, straight and compact fiber into loose and curved fiber with rough surface.展开更多
The precipitation behavior of carbide in K416 B superalloy was investigated by means of creep measurement and microstructure observation. The results show that nanometer M6 C particles discontinuously precipitate in t...The precipitation behavior of carbide in K416 B superalloy was investigated by means of creep measurement and microstructure observation. The results show that nanometer M6 C particles discontinuously precipitate in the γ matrix or along the γ/γ′ interface of the alloy during high temperature tensile creep. Thereinto, the amount of fine M6 C carbide increases as creep goes on, and the coherent interfaces of M6 C phase precipitating from the γ matrix are {100} and {111} planes. The thermodynamics analysis indicates that the solubility of element carbon in the matrix decreases when the alloy is deformed by the axial tensile stress during creep, so as to cause the carbon segregating in the regions of stress concentration and combining with carbide-forming elements M（W, Co）, which promotes the fine M6 C carbide to precipitate from the γ matrix.展开更多
Based on Chaboche constitutive model,a viscoplastic constitutive model of nickel-based alloy under multiaxial loading is proposed by introducing Lemaitre damage model and non-proportional hardening factor.Lemaitre dam...Based on Chaboche constitutive model,a viscoplastic constitutive model of nickel-based alloy under multiaxial loading is proposed by introducing Lemaitre damage model and non-proportional hardening factor.Lemaitre damage model can characterize the effect of microscopic defects on the fatigue behavior and non-proportional hardening factor is used to describe non-proportional hardening phenomenon.Subsequently,the stress–strain hysteresis loops at room and high temperatures under different loading conditions are simulated by the proposed constitutive model.Comparison between experiments and simulations confirms that the proposed model can reasonably predict the fatigue behavior of nickel-based alloy under different multiaxial loadings.At last,the fatigue life predictions under different multiaxial loadings are investigated,and comparison between experiments and simulations verifies the accuracy of the proposed model.展开更多
The molecular dynamics （MD） simulation and the modified analytical embedded-atom method （MAEAM） were used to study the influence of a He atom on the movement of the（a/2）？110？{111} edge dislocation in Ni. First...The molecular dynamics （MD） simulation and the modified analytical embedded-atom method （MAEAM） were used to study the influence of a He atom on the movement of the（a/2）？110？{111} edge dislocation in Ni. First, the calculated Burgers vector distribution shows that the equilibrium dissociation distance （Ded） and the stacking fault energy （Esf） between two partial edge dislocations are about 25.95 ？ and 108 mJ/m2, respectively. Then, the obtained formation energies （Ef） of a He atom at some different sites demonstrate that the He atom is attracted and repelled in the tension and compression regions, respectively. And the He？dislocation interaction reveals that an interstitial He atom plays a more significant role in the dislocation movement than a substitutional He atom. Finally, it is found that the movement of an interstitial He atom is apparent as the first partial dislocation bypasses and the edge dislocation offers fast-diffusion path for the migration of a He atom.展开更多
文摘In this study, the electrochemical reduction of Y(Ⅲ)on nickel electrode has been investigated. The resultsshow that there are several plateaus for formation of intermetallic compounds preceding reduction peak ofyttrium. A linear relationship between the current and t￣(-1/2) has been obtained, showing that Cottrell's law isobeyed.
基金Project(2010FJ3012)supported by the Science and Technology Plan Foundation of Hunan Province,China
文摘Fibrous particulate precursor was obtained by precipitation transformation in the ternary solution system of ammonium oxalate, nickel chloride and ammonia. The composition and morphology of precursor were characterized by XRD, SEM, IR and DTA/TGA analyses. The results show that the chemical composition and morphology of precursor precipitates at pH=8.4？8.8 are different from those of precursor precipitates at pH=6.0, and the mechanisms of the thermal decomposition of the precursors are different. The effects of various conditions in the process of thermal decomposition, including precursor morphology, atmosphere, temperature and time on the morphology and dispersion degree of obtained nickel powders were studied in detail. The final product inherits the morphology of precursor when the thermal decomposition is conducted under a weakly reducing atmosphere at temperature range of 400？440 °C for 30 min. Fibrous nickel powder can be produced with good dispersion, and its shape changes from smooth, straight and compact fiber into loose and curved fiber with rough surface.
基金Projects(2010CB631200,2010CB631206)supported by the National Basic Research Program of ChinaProject(50931004)supported by the National Natural Science Foundation of China
文摘The precipitation behavior of carbide in K416 B superalloy was investigated by means of creep measurement and microstructure observation. The results show that nanometer M6 C particles discontinuously precipitate in the γ matrix or along the γ/γ′ interface of the alloy during high temperature tensile creep. Thereinto, the amount of fine M6 C carbide increases as creep goes on, and the coherent interfaces of M6 C phase precipitating from the γ matrix are {100} and {111} planes. The thermodynamics analysis indicates that the solubility of element carbon in the matrix decreases when the alloy is deformed by the axial tensile stress during creep, so as to cause the carbon segregating in the regions of stress concentration and combining with carbide-forming elements M（W, Co）, which promotes the fine M6 C carbide to precipitate from the γ matrix.
文摘Based on Chaboche constitutive model,a viscoplastic constitutive model of nickel-based alloy under multiaxial loading is proposed by introducing Lemaitre damage model and non-proportional hardening factor.Lemaitre damage model can characterize the effect of microscopic defects on the fatigue behavior and non-proportional hardening factor is used to describe non-proportional hardening phenomenon.Subsequently,the stress–strain hysteresis loops at room and high temperatures under different loading conditions are simulated by the proposed constitutive model.Comparison between experiments and simulations confirms that the proposed model can reasonably predict the fatigue behavior of nickel-based alloy under different multiaxial loadings.At last,the fatigue life predictions under different multiaxial loadings are investigated,and comparison between experiments and simulations verifies the accuracy of the proposed model.
基金Project(ZL1405)supported by the Talent Project of Lingnan Normal University,China
文摘The molecular dynamics （MD） simulation and the modified analytical embedded-atom method （MAEAM） were used to study the influence of a He atom on the movement of the（a/2）？110？{111} edge dislocation in Ni. First, the calculated Burgers vector distribution shows that the equilibrium dissociation distance （Ded） and the stacking fault energy （Esf） between two partial edge dislocations are about 25.95 ？ and 108 mJ/m2, respectively. Then, the obtained formation energies （Ef） of a He atom at some different sites demonstrate that the He atom is attracted and repelled in the tension and compression regions, respectively. And the He？dislocation interaction reveals that an interstitial He atom plays a more significant role in the dislocation movement than a substitutional He atom. Finally, it is found that the movement of an interstitial He atom is apparent as the first partial dislocation bypasses and the edge dislocation offers fast-diffusion path for the migration of a He atom.
