The nano-scale structure observed by neutron diffraction for the metastable materials synthesized by mechanical alloying

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Recently a considerable amount of work has been performed on the solid-state amorphization process due to mechanical alloying(MA). Teh solid state reaction in the mechanical alloyig process is known to proceed at the interface of different components and thereby to depend on various milling conditions such as milling intensity, the ambient temperature, atmosphere and so on. In this study in order to understanding the mechanism of the mdchanical alloying process the structural observation was carried out mainly by using the advantage of the neutron diffraction technique.The MA of the Cu-Ta system, which is characterized by a positive heat of mixing, was carried out. The formation of an amorphous phase was confirmed by the atomic level structure analysis of neutron diffraction and EXAFS and by the electronic studies through a chage in the superconducting transition in the low-temperature specific heat and XPS valence band structure. The MA or the Cr-Fe and Cr powders under the nitrogen gas atmosphere formed an amorphous phase. The nitrogen atom is located at the center of the polyhedron formed by six Cr atoms and stabilizes the amorphous structure in the Cr-Fe-N and Cr-N systems. The amorphization of the Cu-V system, which is also immiscible, was observed due to the solid-gas reaction during the MA under the nitrogen gas atmosphere. The Mg-Al-Zn, Ni-Zr and Se systems were used to elucidate the effect of the milling intensity and ambient temperature on the formation of the quasicrystal and amorphous phase. It is confirmed that both parameters affect significantly the time necessary to complete the formation of the respective phases. The milling intensity is always found to be effective in shortening the milling time. On the other hand, the ambient temperature affects the formation process more significantly in the system where the crystallization temperature is low.