STRUCTURAL RELAXATION OF ALUMINUM-LANTHANIDE METAL TRANSITION-METAL AMORPHOUS-ALLOYS UPON LOW-TEMPERATURE ANNEALING

Structural relaxation of Al90-xLn(x)Ni10 (Ln = Y, La or Ce) and Al74Ce6Ni10M10 (M = Fe, Co, Ni or Hf) amorphous alloys was examined by differential scanning calorimetry. Changes in the maximum differential specific heat, DELTA-C(p,max), and reversible enthalpy relaxation DELTA-H(endo), with annealing temperature, T(a), show at two-stage relaxation in Al90-xLn(x)Ni10 alloys exhibiting a glass transition, T(g). The two stages include a low-temperature stage that peaks at a T(g) of about 150 K and a high-temperature stage at a temperature just below T(g). By comparing the compositional dependence of DELTA-C(p,max)(T(a)) and DELTA-H(endo)(T(a)) as well as the activation energies, Q(m), for the low- and high-temperature relaxations with the melting temperatures of Al11Ln3 and Al3Ln compounds, the low-temperature relaxation is attributed to a local range atomic rearrangement of the Al-Ni pair with weak bonding and the high-temperature relaxation to the medium-range cooperative atomic regrouping of Al-Ln and Ni-Ln pairs with strong bonding. The high-temperature relaxation is not present in the Al74Ce6Ni10M10 alloys that crystallize before T(g). The low-temperature relaxation peak of the Al74Ce6Ni10M10 alloys shifts to a higher temperatures in the order of Hf < Ni < Co < Fe and this compositional dependence is interpreted by taking the bonding nature of Ce and M atoms into consideration.