Thermal expansion of La-based BMG studied by in situ high-energy X-ray diffraction

Abstract

a b s t r a c tThe present work focuses on the study of the thermal stability of La 62 Al 14 (Cu 5/6 Ag 1/6 ) 14 Ni 5 Co 5 (at.%) bulk metallic glass (BMG) using the state-of-the-art high temperature in situ hard X-ray scattering techniques available at the undulator beamline ID11 of ESRF (Grenoble, France). Constant-rate heating experiments using a fast X-ray camera (time resolution of 3 s) reveal detailed information about the thermal stability of the La-based BMG. Analyzing diffraction patterns in a reciprocal space yields thermal expansion of amorphous alloy providing insight about the thermally activated relaxation effects and glass transition. We found that in the region 20 K below the glass transition (T g = 420 K) thermal expansion curve exhibits negative slope which indicates annealing-out of the quenched-in free volumes. The glass transition appears as a brake in the value of coefficient of the volume thermal expansion˛t h . Furthermore, real space analysis based on reduced pair distribution function G(r) allows to trace the changes in the local atomic structure of amorphous material during constant-rate heating.

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

“…In order to erase the sample history we remelted it two times by heating up to 823 K and cooling down to room temperature. From the measurement of the thermal expansion in the molten state (not shown here) we see that thermal cycling in this temperature range is a fully reversible process [24]. Therefore one can use a single piece of sample for the determination of the Temperature-Time-Transformation (TTT) diagram.…”

Undercooling behavior of Zr–Cu–Ni–Al bulk metallic glasses investigated by in situ synchrotron high energy X-ray diffraction

“…It is not until recently that BMGs with high stability against crystallization have made such measurements tractable [18][19][20]. Particularly benefited from the high resolution and fast data acquisition frequency of the in situ high energy X-ray diffraction (HEXRD), structural evolutions have been increasingly investigated, for example, in heating [21][22][23][24][25], loading [26][27][28][29] and melt cooling [30][31][32].…”

Unveiling the structural arrangements responsible for the atomic dynamics in metallic glasses during physical aging

“…This goal requires a description of the structural and dynamical changes occurring at the atomic level, which is still missing due to limitations in both experiments and numerical simulations. Many are the X-ray diffraction (XRD) studies which have investigated the subtle structural changes occurring during aging induced by annealings close to the glass transition temperature T g (refs 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ). The existence of two orthogonal microscopic mechanisms has been highlighted: an irreversible atomic rearrangement, associated with density changes and radial atomic motion observed only in as-cast glasses, quenched with a cooling rate as high as 10 6 K s −1 (hyper-quenching), and a reversible one, not affecting the density, but changing the short range order, taking place also in glasses annealed above T g .…”