Investigation of Amorphization of Nb-Si Alloys by Mechanical Alloying

Amorphous Nb_62.5Si_37.5 and Nb₇₅Si₂₅ alloys were produced from mixtures of elemental Nb and Si powders by mechanical alloying (MA). The structural changes of mechanically alloyed powders were monitored by x-ray diffraction. It was found that NbSi₂ intermetallic compound was formed in the initial stage of MA of Nb_62.5Si_37.5 or Nb₇₅Si₂₅ powders. With continued milling, the mixtures of intermetallic NbSi₂ and elemental Nb transformed into amorphous Nb-Si alloys (Nb_62.5Si_37.5 or Nb₇₅Si₂₅). The slow interdiffusion of Nb and Si and the slower diffusion of silicon atoms to niobium matrix than that of niobium atoms to silicon matrix were suggested to be responsible for the formation of intermetallic NbSi₂. The amorphization of 3NbSi₂ + 7Nb mixtures (or NbSi₂ + 5Nb mixtures) is believed to be controlled by material transfer, which moves composition of line intermetallic NbSi₂ off stoichiometry, and causes the matrix of elemental Nb deformed.