# Thermal and Thermomechanical Analysis of Amorphous Metals: A Compact Review
## 4 In Situ Temperature-Dependent Structural Characterization of Amorphous Metals
### Medium-Range Order and Bridging the Gap between the Precursor Treatment and Application Properties  
[PERSON] et al. studied the change in structure of Pd40 Cu30 Ni10P20 metallic glass during thermal annealing in situ via synchrotron X-ray diffraction. They confirmed that in the glassy state, thermal expansion is accompanied by atomic rearrangements and an increase in larger interatomic distances [83]. Using small-angle neutron scattering combined with X-ray diffraction, [PERSON] et al. studied the safe temperatures at which a Fe48 Cr15 Mo14Y2C15B6 bulk metallic glass can operate by spark plasma sintering the samples to up to 800 \({}^{\circ}\)C [84]. X-ray diffraction showed the appearance of (Fe,Cr)23C6 crystals, while the measured scattering intensity, which was fitted to a size distribution model based on the maximum entropy model, showed that the formed crystals were in the size range between 3 and 18 nm, and that they originated from already pre-existing nuclei formed during the rapid quenching process. This was concluded from a kinetics study, which was performed on behalf of the size distributions that were obtained from the measurements (Figure 5).  
To investigate the influence of transition metals on the formation of Al85 TM10Y5 amorphous alloys (where TM corresponds to Ni, Fe, Cr, and Cu) prepared by melt spinning, [PERSON] et al. also employed laboratory-source X-ray diffraction and performed in situ experiments up to 500 \({}^{\circ}\)C, correlated with differential thermal analysis (DTA) and dynamic  
Figure 5: (**A**) Logarithm plot of in situ small-angle neutron scattering intensity measured over a small Q range at different temperatures; (**B**) the size distribution of newly formed particles during isothermal crystallization of the spark-plasma-sintered glass also confirmed by (**C**) TEM images of the formed crystals at (**a**) 700 \({}^{\circ}\)C and (**b**) 725 \({}^{\circ}\)C and selected area diffraction patterns of crystals formed at (**c**) 700 \({}^{\circ}\)C and (**d**) 725 \({}^{\circ}\)C (reprinted with permission via CC Attribution 4.0 License; multiple Figures were merged for a better overview of the Authors work) [84].  
mechanical analysis (DMA). A negative impact on GFA with Cr addition was observed. They were able to distinguish the material with the best anticorrosive properties and determine that the precipitation crystallization of the YCrAl phase as well as the presence of Cu shows the better anticorrosion properties when compared to the homogeneous, completely amorphous samples. Their research shows the need for only a few techniques to completely describe and determine the processing parameters and range of stability (time and temperature related) [85].  
Challenges of the Advanced In Situ Temperature-Dependent Structural Methods for the Case of Amorphous Metals  
While these techniques are useful for linking processing to the resulting application properties, replicating quenching is challenging from both the standpoint of inducing rapid temperature changes and obtaining accurate time-resolved spectra. Another issue to overcome lies in the inaccessibility of the techniques, which are also spatially resolved and provide information fine enough to study the complex amorphous structure of these materials. The reason there are not many studies conducted in this nature most likely lies in the fact that the combination of in situ temperature control with state-of-the-art spectroscopy or diffraction techniques equipped with detectors and sensors that can detect the signal of the faint medium-range order is financially impossible for most groups, especially when considering that these studies usually only bring rise to discoveries for niche applications.