Characteristics of the mechanically-alloyed Ni60Ti40 amorphous powders during mechanical milling in different atmospheres

Abstract

Mechanically alloyed Ni60Ti40 amorphous powders were further milled in argon, nitrogen and oxygen atmospheres. X-ray diffraction, differential scanning calorimetry and transmission electron microscopy analyses were made to investigate the structural changes during each process. No distinguishable structural changes during further milling of the amorphous powders in argon or nitrogen atmospheres were observed. However, in an oxygen atmosphere, the amorphous phase was crystallized into intermetallic compounds and was accompanied by the occurrence of titanium oxides in the initial stage. On further milling in an oxygen atmosphere, the intermetallic compounds decomposed and only the nickel saturation solution and titanium oxides remained. A thermodynamic explanation of the crystallization and decomposition has been proposed.