Structural study of conventional and bulk metallic glasses during annealing

Abstract

Metallic glasses with conventional glass-forming ability (Al-Fe-Nd, Fe-Zr-B, Fe-B-Nb compositions) and bulk metallic glasses (Ca-Mg-Cu compositions) were studied by synchrotron X-ray diffraction during annealing throughout glass transition and crystallization temperatures.The analysis of the first diffraction peak position during the annealing process allowed us to follow the free volume change during relaxation and glass transition. The structure factor and the radial distribution function of the glasses were obtained from the X-ray measurements. The structural changes occurred during annealing are analyzed and discussed.

Characteristic free volume change of bulk metallic glasses

“…2(a) that it is difficult to observe the free volume change from the experimental DIL trace directly because it is concealed by the comparatively larger linear thermal expansion. 11,[18][19][20][21][26][27][28]41 Fig. 2(b) shows the similarity of the DSC traces and the thermal expansion coefficient a L ðTÞ trace above the onset crystallization temperature T x-on .…”

“…In addition, the alternative relaxed amorphous state is employed in the room temperature density and maximum wave-vector methods. 8,[15][16][17][18][19][20][21] The free volume generated in the glass transition process of the relaxed amorphous state, however, is greater than that of the as-cast amorphous state.…”

“…1(b), because of sample softening above T a-p in the DIL test. The thermal expansion in the glass transition process and subsequent super-cooled liquid region could be measured without the sample softening effect using the synchrotron radiation XRD method [18][19][20][21] or a non-contact DIL instrument. 41 The clear T sr-on below and above which there is an obvious linear and deviating thermal expansion, respectively, can be found for various compositions.…”

“…41 The clear T sr-on below and above which there is an obvious linear and deviating thermal expansion, respectively, can be found for various compositions. [18][19][20][21]41 Hence, if the hypothesized thermal expansion rather than the relaxed sample thermal expansion is taken as the reference, then it is hoped that DV f-gt and the subsequent free volume generation with a constant rate in the super-cooled liquid region shown in Fig. 1(b) can be quantified accurately using a non-contact DIL instrument.…”

“…The change in the maximum wave-vector ðQ max ðT room ÞÞ=Q max ðTÞ ½ 3 , which is measured by real-time high-energy synchrotron radiation x-ray diffraction (XRD), is equal to the volume change ðVðTÞÞ=VðT room Þ ½ . The DV f ðTÞ between the as-cast and relaxed states of BMGs can be quantified in situ as the ðQ max ðT room ÞÞ=Q max ðTÞ ½ 3 difference between the heating and reheating processes at glass transition temperature T g , according to the work carried out by Yavari et al [18][19][20][21] However, this method does not clearly articulate how the free volume changes in the glass transition process because both the as-cast and reference relaxed amorphous states undergo glass transition. The development of a DV f ðTÞ measurement that is real-time and allows convenient comparisons among different compositions thus remains a challenge.…”