CHARACTERISTICS OF THE MECHANICALLY-ALLOYED NI60TI40 AMORPHOUS POWDERS DURING MECHANICAL MILLING IN DIFFERENT ATMOSPHERES

Mechanically alloyed Ni60Ti40 amorphous powders were further milled in argon, nitrogen and oxygen atmospheres. X-ray diffraction, differenti al scanning calorimetry and transmission electron microscopy analyses were made to investigate the structural changes during each process. N o distinguishable structural changes during further milling of the amo rphous powders in argon or nitrogen atmospheres were observed. However , in an oxygen atmosphere, the amorphous phase was crystallized into i ntermetallic compounds and was accompanied by the occurrence of titani um oxides in the initial stage. On further milling in an oxygen atmosp here, the intermetallic compounds decomposed and only the nickel satur ation solution and titanium oxides remained. A thermodynamic explanati on of the crystallization and decomposition has been proposed.