Competitive devitrification and metastable phase selection in amorphous Al–Sm

Monitoring eutectoid decomposition process of metastable phases in Al-Sm alloy via in-situ X-ray scattering and ex-situ transmission electron microscopy

“…Like other Al-based metallic glasses produced by quenching, a clear glass transition is not detected in present study and three exothermic events representing three phase transformations between 300 K and 773 K are clearly observed. Onset temperature for the first exothermic peak is 491 K, which is very close to previous report [9]. Three peak temperatures for three different exothermic events are 501 K, 558 K and 713 K, respectively.…”

“…Since SAXS reflects the electronic density fluctuation and enables to provide insight of chemical separation in the materials, minimal SAXS change at first exothermic event suggests the transformation from amorphous to -Al60Sm11 is nearly chemically partitionless, which has been confirmed by TEM observation in our previous studies [9,14].…”

“…Enhanced mechanical properties can be achieved by growing Al nano-crystals out of an originally amorphous matrix by controlling the solidification [5] and devitrification [6,7] from the glassy state. How processing marginal glasses effect phase selection remains an open question [8][9][10]. Generally, phase and microstructure selection upon annealing involves many metastable phases in Al-based metallic glasses [11][12][13] which is both a challenge and an opportunity.…”

“…A typical phase transformation in far-from equilibrium systems (e.g., devitrification) involves many coexistent, metastable structures at certain chemical compositions and temperatures. For example, the -Al60Sm11 is a bcc phase with lattice parameter of a=13.9 Å, is favored in Al-Sm metallic glass upon heating and decomposes into other metastable phase before finally forming an equilibrium phases [9,13]. Phase transformation among different metastable phases is a balance between formation energies and kinetic effects that can vary depending on the initial state of the amorphous alloy and the time/temperature profile during devitrification.…”

Unveiling the mechanism of phase and morphology selections during the devitrification of Al-Sm amorphous ribbon

“…Devitrification by reheating glass systems can have an asymmetric behavior in the phase selection compared with the crystallization by cooling from the liquid, emphasizing the complex competition between thermodynamics and kinetics [2,3]. Solidification or devitrification under far-from-equilibrium conditions can often lead to unexpected phase selection and microstructures [4][5][6], which is of vital importance in the design of materials with tailored structures and properties. Understanding its fundamental physics of transformation pathways by which different microstructures evolve as a function of increasing departure from equilibrium is essential.…”