The observations of grain-boundary segregation of Bi in Cu bicrystals were analyzed. According to equilibrium grain boundary segregation （EGS） model and non-equilibrium grain-boundary segregation （NGS） model, resp...The observations of grain-boundary segregation of Bi in Cu bicrystals were analyzed. According to equilibrium grain boundary segregation （EGS） model and non-equilibrium grain-boundary segregation （NGS） model, respectively, the segregation kinetics of isothermal annealing at 500 ＆#176;C and that of isochronal annealing for 24 h of Bi in Cu bicrystals were investigated. By qualitative analysis and quantitative analysis, it is concluded that the grain-boundary segregation of Bi agrees well with the theory of NGS. Based on the kinetics model of NGS, some parameters that are useful to predicting and controlling the Bi-induced embrittlement in Cu alloys are calculated as follows：the diffusion coefficient of Bi-vacancy complexes Dc=7.8×10^-5exp[-1.46/（kT）];the apparent diffusion coefficient of Bi atoms Di^A=7.66×10^at＋bexp[–1.76/（kT）], where a=8.45×10^-8 and b=-13.37.展开更多
Electroplating has been used to produce Cu-Bi coatings. The crystal structure and lattice parameters of Cu in Cu-Bi composite coating were measured and compared with Cu coating. The mechanical properties of the coatin...Electroplating has been used to produce Cu-Bi coatings. The crystal structure and lattice parameters of Cu in Cu-Bi composite coating were measured and compared with Cu coating. The mechanical properties of the coatings were also studied. It was found that the deposition parameters have significant effect on the mechanical properties of the Cu-Bi coatings. The microhardness has been improved from HVso165 of Cu coating to HVs0 250 of Cu-Bi composite coating prepared at 50 mA/cm2 for 20 min. Correspondingly, wear resistance of the Cu-Bi composite coating has also been enhanced significantly.展开更多
The effect of direct electric current on the wetting behavior of molten Bi on Cu substrate at 370℃ was investigated by the sessile drop method. The wettability of molten Bi on Cu without an applied current is poor an...The effect of direct electric current on the wetting behavior of molten Bi on Cu substrate at 370℃ was investigated by the sessile drop method. The wettability of molten Bi on Cu without an applied current is poor and the spreading time required to form the steady-state contact angle （about 102°） is approximately 30 min. With the increase of the applied electric current, the spreading of molten Bi on Cu is accelerated significantly and the steady-state contact angle decreases considerably. The cross-section SEM micrographs of the solidified Bi droplet on Cu substrate show that the electric current has a marked effect on the convection of melt. Correspondingly, the application of an electric current obviously enhances the dissolution of Cu into Bi melt, which may change the wetting triple line configuration. The improvement of wettability induced by electric current is also related to the additional driving force for wetting provided by the electromagnetic pressure gradient force.展开更多
基金Project(51001011)supported by the National Natural Science Foundation of ChinaProject(141043)supported by the Fok Ying-Tong Education Foundation,ChinaProject(FRF-TP-12-042A)supported by the Fundamental Research Funds for the Central Universities,China
文摘The observations of grain-boundary segregation of Bi in Cu bicrystals were analyzed. According to equilibrium grain boundary segregation （EGS） model and non-equilibrium grain-boundary segregation （NGS） model, respectively, the segregation kinetics of isothermal annealing at 500 ＆#176;C and that of isochronal annealing for 24 h of Bi in Cu bicrystals were investigated. By qualitative analysis and quantitative analysis, it is concluded that the grain-boundary segregation of Bi agrees well with the theory of NGS. Based on the kinetics model of NGS, some parameters that are useful to predicting and controlling the Bi-induced embrittlement in Cu alloys are calculated as follows：the diffusion coefficient of Bi-vacancy complexes Dc=7.8×10^-5exp[-1.46/（kT）];the apparent diffusion coefficient of Bi atoms Di^A=7.66×10^at＋bexp[–1.76/（kT）], where a=8.45×10^-8 and b=-13.37.
基金Bright Sparks Unit,University Malaya for the financial support
文摘Electroplating has been used to produce Cu-Bi coatings. The crystal structure and lattice parameters of Cu in Cu-Bi composite coating were measured and compared with Cu coating. The mechanical properties of the coatings were also studied. It was found that the deposition parameters have significant effect on the mechanical properties of the Cu-Bi coatings. The microhardness has been improved from HVso165 of Cu coating to HVs0 250 of Cu-Bi composite coating prepared at 50 mA/cm2 for 20 min. Correspondingly, wear resistance of the Cu-Bi composite coating has also been enhanced significantly.
基金Project(50704001) supported by the National Natural Science Foundation of China
文摘The effect of direct electric current on the wetting behavior of molten Bi on Cu substrate at 370℃ was investigated by the sessile drop method. The wettability of molten Bi on Cu without an applied current is poor and the spreading time required to form the steady-state contact angle （about 102°） is approximately 30 min. With the increase of the applied electric current, the spreading of molten Bi on Cu is accelerated significantly and the steady-state contact angle decreases considerably. The cross-section SEM micrographs of the solidified Bi droplet on Cu substrate show that the electric current has a marked effect on the convection of melt. Correspondingly, the application of an electric current obviously enhances the dissolution of Cu into Bi melt, which may change the wetting triple line configuration. The improvement of wettability induced by electric current is also related to the additional driving force for wetting provided by the electromagnetic pressure gradient force.
