Kinetics and Mechanisms of Isothermal Devitrification in Amorphous Cu50Zr50

Abstract

The crystallization kinetics and microstructural dynamics associated with devitrifying a meltspun Cu 50 Zr 50 metallic glass were investigated using isothermal treatments, in situ high-energy synchrotron X-ray diffraction, conventional and high-resolution transmission electron microscopy, and differential scanning calorimetry. The analysis of isothermal transformations allows us to more clearly unravel the complex interplay between nucleation and growth of competing stable and metastable phases. The isothermal devitrification response was found to involve the Cu 10 Zr 7 , CuZr 2 , and CuZr phases, consistent with previously reported constant heating rate experiments, but here we have resolved the phase evolution and structural characteristics of the transformation, including the very early stages of crystallization. At 671 K (398°C), the isothermal transformation starts with the formation of the Cu 10 Zr 7 phase, which grows in a generally equiaxed morphology. At a size of approximately 100 nm, the growth of the Cu 10 Zr 7 particles is interrupted by the precipitation of a thin layer of the CuZr 2 phase, upon which the metastable CuZr (B2) grows epitaxially. Crystallization kinetics are quantified here though in situ measurements (HEXRD, DSC) and ex situ microstructural analysis (TEM, HRTEM). Finally, the influences of chemical partitioning, diffusion, and crystallographic orientation on this sequence are examined.

Crystallization behavior upon heating and cooling in Cu50Zr50 metallic glass thin films

“…2c) prior to the XRD measurement. Our data and recent in-situ XRD results [37,38] indicate that this phase is not likely formed during heating, but instead forms on cooling. is larger than that of a relaxed metallic glass (R-MG) because the effective quench rate during deposition of the S-MG is much higher than that of the R-MG.…”

“…2a has an endothermic peak (T rxn ) at 1027 ± 5 K. This peak cannot be indexed as any of the melting temperatures of the crystalline phases in the Cu-Zr phase diagram [32][33][34]. Instead, the phase diagram and recent high-resolution insitu XRD measurements on bulk Cu 50 Zr 50 metallic glasses [37,38] and then quenched ( Fig. 2c) prior to the XRD measurement.…”

On Long-Term Stability of Metallic Glasses

“…Crystallization [37,38] and electrochemical corrosion [39,40] of the Zr 50 Cu 50 glassy alloy were studied extensively. A recent work particularly reflected its complicated crystallization behavior [41]. Higher Cu content causes an increase in the passivation current of Cu-Zr glassy alloys [42].…”

Crystallization dynamics in glass-forming systems

“…A more recent study by Cullinan et al [64] 6 utilized carefully selected isothermal annealing treatments that resulted in a slower transformation, allowing the initial crystallization sequence to be resolved through in-situ HEXRD measurements and electron microscopy of specimens that were quenched at different times throughout the annealing (see Fig. A.2b).…”

“…1.3, the crystalline phase fractions at the end of the isothermal transformation are consistent with those measured at the beginning of the constant-heating rate transformation. The approach taken by these related studies [6,64] 9 provides a view of the crystallization process backed by direct experimental data with never-before achieved fidelity.…”