Thermal expansion of a La-based bulk metallic glass: insight fromin situhigh-energy x-ray diffraction

Abstract

Constant-rate heating experiments using a fast x-ray camera (time resolution of 2.7 s) reveal detailed information about the thermal stability of La 62 Al 14 (Cu 5/6 Ag 1/6 ) 14 Ni 5 Co 5 (at.%) bulk metallic glass. Analyzing diffraction patterns in reciprocal space yields the thermal expansion of the amorphous alloy providing insight about the thermally activated relaxation effects and kinetics of the glass transition. The glass transition appears as a break in the value of the coefficient of volume thermal expansion. Furthermore, real space analysis based on reduced pair distribution function G(r) allows one to follow in-situ the changes in the local atomic structure of the amorphous material during constant-rate heating.

Liquid–liquid transition in a strong bulk metallic glass-forming liquid

“…3a. The first peak position of the structure factor, Q 1 , corresponds to the length scale of medium-range order correlations in real space 29 . In Fig.…”

“…Thus, the length scale of the structural transformation in the supercooled state is likely not less than the 4th shell distance (Z1 nm) and can be reflected in by Q 1 of S(Q) in reciprocal space (Fig. 3b), which is demonstrated to be more sensitive to medium/long range correlations 29 . It is hardly a coincidence that the length of the ideal face-centered-cubic (FCC)-like cluster-unit-cell for the medium-range order of Miracle's efficient cluster packing model 47 is calculated to be around 1.0-1.3 nm.…”

Structural and dynamical properties of Mg65Cu25Y10 metallic glasses studied by in situ high energy X-ray diffraction and time resolved X-ray photon correlation spectroscopy

“…Unfortunately due to technical problems part of the data acquired during the first cooling rate have been lost, without however affecting the presented results. As previously discussed, rapidly quenched metallic glasses keep excess free volume or internal stresses which can be released with the first annealing [10][11][12][13][14][15][16][17]. This phenomenology is due to the intrinsic kinetic nature of the glass transition, and the consequent dependence of Tg on the cooling rate [4,24].…”

“…This phenomenology is due to the intrinsic kinetic nature of the glass transition, and the consequent dependence of Tg on the cooling rate [4,24]. Assuming the atomic environments does not suffer important changes during the annealing, the position of the FSDP can be related to the relative volume change in the material as V/V0=(q0/q) 3 [14][15][16][17]. However, recently, it has been shown that for densely packed metallic glasses this interpretation is not unambiguous and other parameters, such as the FSDP intensity and width can give a clearer indication of the occurrence of structural changes [23].…”

“…Quantitative information on the presence of extra free volume and its annihilation process under thermal treatment have been usually obtained from high energy X-ray diffraction studies, by following the evolution of static structure factor S(q) for different thermal paths [14][15][16][17]. The internal stresses associated to the extra free volume are most likely the reason of the fast exponential physical aging recently observed in the atomic motion of rapidly quenched metallic glasses [8,18,19].…”