Local atomic order in Al-based metallic glasses studied using XAFS method

Local atomic order in series of Al-(Y, Sm)-TM (TM = transition metal: Co, Ni) amorphous, melt-spun alloys was investigated by Sm L-3-edge and TM K-edge X-ray absorption fine structure (XAFS) method. The evaluated coordination number of Sm is approximately 16 for all investigated systems and TM coordination ranges form 5 to 6. A slight decrease in TM coordination along with increase of TM content is observed. The interatomic distances between Al and Sm atoms are equal to the sum of their metallic radii within the experimental error, while Al-TM bonds are shortened by 10%. The structural disorder around Sm atoms is significantly higher then around TM. We have found that only Al atoms are present in the first coordination shell of both Sm and TM species. The XAFS data show that the amorphous network coherency is lost at distances exceeding 4 A. The results are discussed in a framework of Miracle's structural model of metallic glasses suggesting that the average local structure around Sin atoms consists of 16 efficiently packed Al atoms in the first coordination shelf of Sm and the TM atoms occupy the octahedral sites in the closely packed fcc cluster structure. (c) 2008 Elsevier B.V. All rights reserved.