Ultrastable metallic glasses formed on cold substrates

Abstract

Vitrification from physical vapor deposition is known to be an efficient way for tuning the kinetic and thermodynamic stability of glasses and significantly improve their properties. There is a general consensus that preparing stable glasses requires the use of high substrate temperatures close to the glass transition one, T_g. Here, we challenge this empirical rule by showing the formation of Zr-based ultrastable metallic glasses (MGs) at room temperature, i.e., with a substrate temperature of only 0.43T_g. By carefully controlling the deposition rate, we can improve the stability of the obtained glasses to higher values. In contrast to conventional quenched glasses, the ultrastable MGs exhibit a large increase of T_g of ∼60 K, stronger resistance against crystallization, and more homogeneous structure with less order at longer distances. Our study circumvents the limitation of substrate temperature for developing ultrastable glasses, and provides deeper insight into glasses stability and their surface dynamics.

Fig. 1

Effect of vitrification routes on the glass transition and crystallization. a Representative DSC traces at a heating rate of 20 K min⁻¹ for Zr₄₆Cu₄₆Al₈ MGs: ordinary glass produced by melt-spinning technic; vapor-deposited glass films at different rates as denoted below each curve. T_g and T_x are defined from the onset of the transformation as indicated by the intersection of the black lines. b T_g vs. R. The solid line at high R is an exponential fit to the data, at low R the T_g keeps invariant. Inset: T_x vs. R. The error bars indicate the standard deviation of three to five measurements. For comparison, the T_g and T_x with their variation ranges for the ordinary glass are presented by the shaded magenta areas

Fig. 2

Crystallization dynamics and phase formation of the ordinary and the ultrastable glasses upon annealing. a, b XRD profiles for as-prepared and annealed a ordinary and b 0.80 nm min⁻¹ deposited ultrastable MGs. The annealing temperature and time are denoted by the legend values above each curve. Inset in b: XRD data for as-deposited and annealed ultrastable MGs and as-quenched ordinary MGs plotted as a function of q = 4πsinθ/λ. The vertical lines indicate the peak positions. c XRD profiles for samples after annealed at 973 K for 1 h, from top to bottom, the ordinary, 5.69 nm min⁻¹, 1.76 nm min⁻¹, and 0.80 nm min⁻¹ vapor-deposited glasses. Inset: DSC traces for the ordinary and the 0.80 nm min⁻¹ deposited glasses at a heating rate of 20 K min⁻¹

Fig. 3

Structure characterization for the ordinary and the 0.80 nm min⁻¹ deposited ultrastable glasses. a Pair distribution function G(r) and static structure factor S(q) (the inset) for the ordinary and the ultrastable MGs. b, c HRTEM images of b the ordinary and c the ultrastable MGs. Insets: selected area electron diffraction (SAED) patterns taken from a large selected area. d, e HADDF-STEM images of d the ordinary and e the ultrastable MGs. The scale bars in b–e are 5 nm

Fig. 4

Comparison of surface relaxation with bulk α and β relaxations. The magenta and purple curves along with the open circles show the bulk α and β relaxation rates vs. T_g/T in MGs, respectively. The solid square, star, and circle show the surface relaxation rate Γ_surface vs. T_g/T_sub estimated from vapor deposition of an ultrastable molecular glass, the Zr-MG of ref. , and the sample studied in the present work, respectively. The rhombuses are for ethylcyclohexane glass as Γ_surface is the inverse critical free surface residence time at which the time of isothermal transformation from the glass into the supercooled liquid state reaches the plateau (Figure 9 in ref. ). The Γ_surface from STM measurements are plotted as pentagons (left one: La₅₀Ni₁₅Al₂₅Cu₁₀, right one: La₆₀Ni₁₅Al₂₅ MGs) and as triangles (Fe₇₈B₁₃Si₉ MG^, ). The blue line is a linear fit to the surface relaxation rates