Early Stages of Solid-State Amorphization Reaction During Mechanical Alloying of a Multicomponent Zr-Powder Mixture

• Published in: Scripta materialia 1997-12, Vol.38 (1), p.163-169
• Main Authors: Sagel, A., Wanderka, N., Wunderlich, R.K., Schubert-Bischoff, P., Fecht, H.-J.
• Format: Article
• Language: English
• ISSN: 1359-6462; 1872-8456
• DOI: 10.1016/S1359-6462(97)00408-9

In order to allow for a meaningful comparison of the thermal stability and compositional homogeneity of mechanical alloyed amorphous powders with that of metallic glasses of the same average composition prepared by rapid liquid quenching, it is essential to develop a clear understanding of the microstructural evolution and phase formation during ball milling. This issue is addressed in the present work by showing detailed structural investigations on the early stages of phase formation during mechanical alloying of an elemental Zr sub 60 Al sub 10 Ni sub 9 Cu sub 18 Co sub 3 powder mixture. The results reveal that formation of strongly supersaturated solid solutions and fast grain refinement are the prior steps before the onset of amorphization. It is concluded that mechanical alloying of the multicomponent Zr-Al-Ni-Cu-Co powder is an inherent inhomogenous process. This implies that the early stages of the solid-state amorphization reacton cannot be investigated sufficiently with standard analytical methods such as x-ray diffraction of DSC. The results presented from TEM investigations have shown that grain refinement and the formation of highly supersaturated nanocrystalline solid solutions are the prior steps before the amorphization starts. After a very short milling time amorphization is localized at the interfaces of supersaturated alpha -Zr nanocrystals. During further ball milling a variety of amorphous phases with different compositions are formed which can be homogenized by continued milling.