The normally centered electron beam and non-centered electron beam welding of TiAl to TC4 was investigated in order to analyze the electron beam weldability between TiAl/TC4 dissimilar materials. Macroscopic cold crac...The normally centered electron beam and non-centered electron beam welding of TiAl to TC4 was investigated in order to analyze the electron beam weldability between TiAl/TC4 dissimilar materials. Macroscopic cold crack easily occurred near TiAl substrate in the joints. The optimal tensile strength was related to the welding heat input. The weld structures were composed of bulky columnar grains and equiaxed grains. The isolated phases consisted of large quantities of α2 -Ti3Al phase, small quantity of B2 phase, γ-TiAl phase and YAl2 phase. Insufficient melting of the base metal occurred in the weld when the beam position leaned to the TC4 side. The tensile strength could be improved when the deflection was limited in the optimum range. Otherwise, non-fusion zone was easily generated in the weld, which led to the low tensile strength.展开更多
The equilibrium structures and electronic structure of LaNi5-xGax （x=0, 0.5, 1.0） compounds have been investigated by all-electron calculations. Based on the full geometry optimization, the densities of states and e...The equilibrium structures and electronic structure of LaNi5-xGax （x=0, 0.5, 1.0） compounds have been investigated by all-electron calculations. Based on the full geometry optimization, the densities of states and electron densities of LaNi5-xGax are plotted and analyzed. It is clear that the substitution of Ga at the Ni site leads to a progressive filling of the Ni-d bands, the ionic interaction between Ni and Ni, with Ga plays a dominant role in the stability of LaNi5-xGax compounds. The smaller the shift of EF toward higher energy region, the more stable the compounds will be. The increased contribution of the Ni-d-Ga-d interactions near EF and the low energy metal-gallium bonding bands indicate that the compounds become more stable. The results are compared with experimental data and discussed in light of previous studies.展开更多
文摘The normally centered electron beam and non-centered electron beam welding of TiAl to TC4 was investigated in order to analyze the electron beam weldability between TiAl/TC4 dissimilar materials. Macroscopic cold crack easily occurred near TiAl substrate in the joints. The optimal tensile strength was related to the welding heat input. The weld structures were composed of bulky columnar grains and equiaxed grains. The isolated phases consisted of large quantities of α2 -Ti3Al phase, small quantity of B2 phase, γ-TiAl phase and YAl2 phase. Insufficient melting of the base metal occurred in the weld when the beam position leaned to the TC4 side. The tensile strength could be improved when the deflection was limited in the optimum range. Otherwise, non-fusion zone was easily generated in the weld, which led to the low tensile strength.
基金This work was financially supported by the National Natural Science Foundation of China （No.60777012）.
文摘The equilibrium structures and electronic structure of LaNi5-xGax （x=0, 0.5, 1.0） compounds have been investigated by all-electron calculations. Based on the full geometry optimization, the densities of states and electron densities of LaNi5-xGax are plotted and analyzed. It is clear that the substitution of Ga at the Ni site leads to a progressive filling of the Ni-d bands, the ionic interaction between Ni and Ni, with Ga plays a dominant role in the stability of LaNi5-xGax compounds. The smaller the shift of EF toward higher energy region, the more stable the compounds will be. The increased contribution of the Ni-d-Ga-d interactions near EF and the low energy metal-gallium bonding bands indicate that the compounds become more stable. The results are compared with experimental data and discussed in light of previous studies.
