Study of Nano-Clustering Mechanism by Positron Annihilation and 3D Atom Probe

本研究的目的是用正电子湮没和三维原子探针(3DAP)分析材料中纳米团簇的形成机制、空位-溶质复合体的形成和团簇形成的动力学。我们得到了以下结果：1)制备了Fe-Cu、Al-Ag、Al-Zn等单晶和多晶样品。2)用正电子湮没和3DAP技术研究了Al-Cu-Mg中溶质团簇的预析出过程。Al-铜-镁-银和铝-锂-铜-镁-银合金。不仅通过3DAP观察溶质团簇，而且通过正电子寿命和正电子湮没符合多普勒展宽(CDB)检测淬入空位及其空位-溶质复合体，揭示了空位-溶质相互作用在Al合金析出早期溶质聚集中的作用。目前的成功表明，正电子湮没和3DAP相结合对于研究溶质团簇的形成机制是非常有用的。3)正电子湮没辐射的二维角关联测量揭示了嵌入纳米团簇的费米表面拓扑。通过将实验结果与第一性原理计算结果进行比较，我们提出了一种确定嵌入团簇中溶质浓度的新规则：类似Peiers扭曲的带隙效应和Hume-Rothery规则。4)利用东北大学Oarai中心的正电子年龄-动量关联测量和正电子扩散计算，提出了估算亚纳米团簇数密度的新方法。

The purpose of the present study is to analyze the formation mechanism of nano-clusters in materials, the formation of vacancy-solute complexes and the kinetics of the cluster formation through the migration of the complexes, never revealed by conventional methods, by using positron annihilation and three-dimensional atom probe (3DAP).We have obtained the following results :1) The specimens, Fe-Cu, Al-Ag, Al-Zn etc. single crystals and polycrystals, were prepared.2) Positron annihilation and 3DAP techniques are employed to investigate the pre-precipitation of solute clustering in Al-Cu-Mg, Al-Cu-Mg-Ag and Al-Li-Cu-Mg-Ag alloys. Not only by observing the solute clusters using 3DAP but also by detecting quenched-in vacancies and their vacancy-solute complexes using positron lifetime and coincidence Doppler broadening (CDB) of positron annihilation, we reveal the effect of vacancy-solute interactions in the solute clustering in the early stage of the precipitation in the Al alloys. The present success shows that the combination of positron annihilation and 3DAP is very useful to study the mechanism of the solute clustering.3) Two-dimensional angular correlation of positron annihilation radiation (2D-ACAR) measurements revealed Fermi surface topology of embedded nano-clusters. By comparing experimental results with the first principles calculations, we proposed a new rule to determine the solute concentrations in the embedded clusters : band gap effect analogous of Peiers distortion and Hume-Rothery rule.4) New method to estimate number density of subnano-clusters was developed, combined with positron age-momentum correlation measurements and positron diffusion evaluation by using energy variable positron beam in Oarai Center, Tohoku University.