Research Highlights

A fundamental understanding of how metallic glasses undergo polymorphic crystal growth near their glass-transition temperature (T_g) can lead to the design of novel composite crystal-glassy materials with precise property control.

Further, due to the slow and decoupled atomic diffusion near T_g, experimental studies on metallic glass crystal growth often yield unexpected results. The exact crystallization mechanisms and growth rates—whether controlled by short- or long-scale atomic diffusion—remain to be fully understood.

In a recent article¹, Louzguine et al. from AIMR addressed this problem using a combination of in-situ transmission electron microscopy (TEM), analytical TEM, differential thermal analysis, and differential scanning calorimetry to study the crystallization of a Ti-Ni-Cu-Fe metallic glass at 703 K.

“The key advancement of this work lies in our use of in-situ TEM at 703 K—near T_g of the Ti₅₀Ni₂₂Cu₂₂Fe₆ glass,” explained Prof. Louzguine. “This approach enabled real-time observation of the crystallization process and direct measurement of crystal growth rates at a temperature where atomic diffusion is typically slow.”

The study found that crystal growth rates in the Ti₅₀Ni₂₂Cu₂₂Fe₆ glass (~2 × 10^-10 m/s) were significantly faster than predicted by standard diffusion models.

“Our in-situ TEM study measured the crystal growth rate to be orders of magnitude higher than that allowed by thermal long-range diffusion estimated from viscosity indicating a breakdown of the Stokes–Einstein equation”, says Prof. Louzguine. “We believe the diffusion at the glass/crystal interface, can be accelerated by differences in thermodynamic and chemical potentials between the phases.”

Future work will use this approach to confirm this hypothesis and explore the crystallization of more complex multicomponent alloys, including quasicrystalline phases.

(Author: Patrick Han)