(1. 廣西大學(xué) 物理系， 南寧 530004；
2. 廣西大學(xué) 材料微結(jié)構(gòu)研究所， 南寧530004;
3. 中國科學(xué)院 國際材料物理中心， 沈陽 110015；
4. 中國科學(xué)院 金屬研究所， 沈陽 110015)
摘 要: 測量了TiAl， Ti50Al48Zr2和Ti50Al48Nb2的正電子壽命譜，并利用正電子壽命參數(shù)分別計算了合金基體和缺陷態(tài)的自由電子密度。TiAl合金基體的自由電子密度比金屬Ti和金屬Al基體的低，當(dāng)Ti和Al組成TiAl合金時，Ti原子和Al原子的部分價電子被局域化，TiAl合金中金屬鍵和共價鍵共存。TiAl合金晶界缺陷的開空間較大，晶界缺陷處的自由電子密度較低，金屬鍵結(jié)合力較弱，材料易發(fā)生沿晶脆斷。在TiAl合金中分別加入Nb和Zr元素，合金基體和晶界的自由電子密度升高，有利于抑制合金解理斷裂和沿晶脆斷。
關(guān)鍵字: TiAl合金； 正電子壽命；自由電子密度
（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
