Two glass transitions in mechanical relaxation of a La55Al25Ni20 amorphous alloy

Abstract

Dynamic mechanical properties of a La 55 Al 25 Ni 20 amorphous alloy reveal two relaxation processes in the glass transition region. At a frequency of 62.8 rad/s the loss modulus, E ″, shows two peaks at about 483 and 507 K. With decreasing frequency, the peak temperatures shift lower and the two peaks tend to separate further. Frequency scans also show a main peak at lower frequency and a lower peak at higher frequency as a shoulder. Using the time-temperature superposition process, a master curve of loss modulus has been constructed. Activation energies were calculated from the shift factor and found to be 400 and 550 kJ/mol, respectively, for the higher frequency and lower frequency peak. The occurrence of the two relaxations is associated with spinodal phase separation.