Calorimetry study of the synthesis of amorphous Ni-Ti alloys by mechanical alloying

We synthesized amorphous Ni33Ti67 alloy powder by ball milling (a) a mixture of elemental nickel and titanium powders and (b) powders of the crystalline intermetallic NiTi2. We characterized the reaction products as a function of ball-milling time by differential scanning calorimetry and X-ray diffraction. The measurements suggest that in process (a) the amorphous alloy forms by a solid state interdiffusion reaction at the clean Ni Ti interfaces generated by the mechanical attrition. In process (b), the crystalline alloy powder stores energy in the form of chemical disorder and lattice and point defects. The crystal-to-amorphous transformation occurs when the stored energy reaches a critical value. The achievement of the critical stored energy competes with the dynamic recovery of the lattice. © 1988.