(1. 广西大学 物理系， 南宁 530004；
2. 广西大学 材料微结构研究所， 南宁530004;
3. 中国科学院 国际材料物理中心， 沈阳 110015；
4. 中国科学院 金属研究所， 沈阳 110015)
摘 要: 测量了TiAl， Ti50Al48Zr2和Ti50Al48Nb2的正电子寿命谱，并利用正电子寿命参数分别计算了合金基体和缺陷态的自由电子密度。TiAl合金基体的自由电子密度比金属Ti和金属Al基体的低，当Ti和Al组成TiAl合金时，Ti原子和Al原子的部分价电子被局域化，TiAl合金中金属键和共价键共存。TiAl合金晶界缺陷的开空间较大，晶界缺陷处的自由电子密度较低，金属键结合力较弱，材料易发生沿晶脆断。在TiAl合金中分别加入Nb和Zr元素，合金基体和晶界的自由电子密度升高，有利于抑制合金解理断裂和沿晶脆断。
关键字: TiAl合金； 正电子寿命；自由电子密度
（1. Physics Department， Guangxi University， Nanning 530004, P.R.China;
2. Microstructure Institute of Materials， Guangxi University， Nanning 530004, P.R.China;
3. International Centre for Materials Physics， Chinese Academy of Sciences, Shenyang 110015, P.R.China;
4. Institute of Metal Research， Chinese Academy of Sciences， Shenyang 110015, P.R.China）
Abstract:The positron lifetime spectra ofTiAl， Ti50Al48Zr2 and Ti50Al48Nb2 alloys were measured. The densities of free electronsof the bulk and microdefectsin these alloys were calculated by using the positron lifetime parameters. The density of free electrons is lower in the bulk of TiAl alloy than that of Ti orAl metal which implicates that some valence electrons of Ti and Al atoms are localized when they aggregate to form TiAl alloy. The bonding characteristic of TiAl is a mixture of metallic and covalent. The largeopen defects occur on the grain boundary in TiAl alloy and the bonding strength of grain boundary is weak due to the low density of free electrons there, and the brittle fracture along grain boundary is prone to occur. As TiAl alloy is alloyed with ternary element of Zr or Nb， the densities of freeelectrons in the bulk and the grain boundary will simultaneously increase. The brittle fracture along grain bourdary and cleavage fracture of alloys are restrained.
Key words: TiAl alloy； positron lifetime； density of free electron
