用正电子湮没技术研究不同化学成分的二元TiAl合金中的微观缺陷

Microdefects in binary TiAl alloys with different chemical compositions investigated by positron annihilation technique

测量了铝含量从 4 7at%到 5 3at%的二元TiAl合金的正电子寿命谱。结果表明 :所有测试合金晶界缺陷的开空间均大于金属Al单空位的开空间。富Al的TiAl合金 ,其晶界缺陷的开空间随Al含量的增加而增大 ;晶界处的电子密度随Al含量的增加而降低。富Ti的TiAl合金 ,随着Ti含量的增加 ,其晶界 (或相界 )缺陷的开空间减小 ,晶界处的电子密度增高 ,使得晶界结合力增强。富Ti的TiAl合金中形成了α2 (Ti3Al) +γ(TiAl)层状结构双相组织使相界面增多 ,导致正电子陷阱数增加。讨论了合金的微观结构对其力学性能的影响。

Positron lifetime measurements have been performed in binary TiAl alloys with Al contents from 47at.% to 53at.%. The experiment results indicate that the open volume of defect on grain boundary of all tested TiAl alloys is larger than that of a monovacancy of pure Al metal. In Al-rich TiAl alloys, with the increase of Al content, the open volume of defect on grain boundary increases while the density of free electron decreases. In contrast, in Ti-rich TiAl alloys, with the increase of Ti content, the open volume of defect on grain boundary decreases, and the density of free electron of the grain boundary increases, thus the cohesive strength between the grains increases. The duplex structure, α 2(Ti 3Al)+γ(TiAl), was formed in Ti-rich TiAl alloys, and this give rise to the increase of the phase boundaries and the traps of positron. The effect of the microstructure of the alloy on the mechanical property has been discussed.