中文摘要：

利用正电子湮没寿命谱（PALS）和符合Doppler展宽（CDB）技术研究了Ti51Al49合金中Nb的掺杂效应.结果表明：低含量掺杂时,Nb原子主要偏聚在合金晶界处,提高了晶界位置的自由电子密度,有利于改善合金的室温韧性;而较高含量的Nb掺杂时,由于形成了新的晶体结构,合金基体及晶界处的自由电子密度减少,导致合金的脆性增加.

英文摘要：

Positron annihilation lifetime and coincidence Doppler broadening measurements have been performed for Ti51Al49 alloy with different amounts of Nb. The experimental results indicate that when a low amount of Nb atoms is added into Ti51Al49 alloy, the Nb atoms mainly aggregate at grain boundaries, which increased the free electron density at boundaries and improved the toughness at room temperature of TiAl alloys. In contrast, the densities of free electron at grain boundaries and in bulk decreased for high Nb doped alloy, due to the formation of the new ordering structure, which increases the brittleness of TiAl alloys.