Formation and stability of nanocrystalline alloys synthesized by mechanical milling

Citation

Abe, Yoshio (1993) Formation and stability of nanocrystalline alloys synthesized by mechanical milling. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/td6t-jp61. https://resolver.caltech.edu/CaltechETD:etd-08222007-085631

Abstract

Nanocrystalline materials are expected to have quite different physical properties from both conventional polycrystalline materials and amorphous materials, particularly due to high fraction of grain boundaries. For their application, to improve the stability is of great concern. In this study, nanocrystalline Ti - Cu, Ti - Zr - Cu and Nb - Cu alloys were synthesized by the mechanical alloying technique. Macroscopically, supersaturated single-phase solid solutions were obtained in the form of powder after certain duration of ball milling. The powders obtained were characterized by X-ray diffraction, differential scanning calorimetry, transmission electron microscopy and small angle X-ray scattering. In Ti - Cu and Ti - Zr - Cu systems, crystal grains do not grow by heating until the intermetallic Cu(Ti, Zr)2 phase nucleates, while in Nb - Cu system, grain growth follows the clustering of elemental Cu. These result lead to the hypothesis that grain growth is suppressed due to the segregation of Cu atoms in grain boundaries. Furthermore, the mechanisms of solute segregation in grain boundaries and the stability of the nanocrystalline structure are discussed in terms of the hypothesis that grain boundaries consist of a liquid-like disordered phase. Finally, based on the above argument, we have proposed a new technology, high temperature ball milling, to synthesize nanocrystalline alloys with finer grain size and more stability and to control grain size as desired.

Thesis Files