β relaxation and its composition dependence in Ce-based bulk metallic glasses

Dynamic loss modulus has been measured in both temperature and frequency domains in Ce70GaxCu30 (Y = 6, 8, 10, 11, 12) and Ce70-xAl10Cu20Cox. (x = 1, 2, 3, 5) bulk metallic glasses using dynamic mechanical analyzer (DMA). It is observed that although these Ce-based glasses belong to the 13 relaxation unfavorable systems with large difference of mixing heats among the constituting elements, the estimated mean chemical mixing enthalpy still shows closely related influences on the variation of beta relaxation behaviors. This finding is sharply different with the opposite relation between the mean chemical mixing enthalpy and beta relaxation in the typical alpha relaxation unfavorable Zr-Cu-Al glasses, which also shows similarly large difference of mixing heats of atomic pairs. These results in principle support the idea proposed by H. B. Yu et al. that large mixing enthalpy fluctuations among the constituting elements suppress beta relaxation in metallic glasses. However, it also implies that it is hard to use a simple relation to count the interplay between the mean chemical mixing heat and beta relaxation, especially in beta relaxation unfavorable systems. Thus, more fundamental information concerning the composition dependence of beta relaxation are further required. (c) 2014 Elsevier B.V. All rights reserved.