SUB-TG MECHANICAL RELAXATION OF A LA55AL25NI20 AMORPHOUS ALLOY

Dynamic mechanical properties of an amorphous La55Al25Ni20 alloy were measured by a forced oscillation method in the temperature range from room temperature to 453 K, just below the glass transition temperature (T(g) = 481 K). The internal friction at a constant frequency 62.8 rad/s of this alloy showed a peak at about 400 K and the peak position shifts with frequency. Structural relaxation reduces the magnitude of the relaxation peak but has little affect on the peak position. Using the time-temperature superposition process, master curves for storage E'(ln-omega) and loss E"(ln-omega) moduli are constructed. Activation energy of the relaxation obtained from shift factors is low, approximately 100 kJ/mol, which is close to that for diffusion of the Al in Al and Ni in Al. The relaxation spectra are very broad with a half width of 2 approximately 3 decades.