Bulk Metallic Glass-forming Liquid Research Articles

Viscosity and surface tension of the Zr56.5Ti13.3Ni13.6Cu9.6S7 bulk metallic glass-forming liquid

The viscosity of the Zr56.5Ti13.3Ni13.6Cu9.6S7 bulk glass forming alloy was measured in equilibrium liquid at low and high temperatures. Low temperature measurements were conducted in the vicinity of the glass transition using a thermomechanical analyzer, covering a viscosity range between 109 and 1014 Pa s. The high-temperature experiments were carried out by electromagnetic levitation of a spherical droplet in microgravity during a parabolic flight campaign (TEMPUS), ranging in viscosity from 50 to 800 mPa s. The viscosities were individually modeled using the Vogel–Fulcher–Tammann equation to obtain the fragility parameter D*, which displays a strong liquid behavior of 25.8 and 19.6 for the low and high temperature region, respectively. The Mauro–Yue–Ellison–Gupta–Allan viscosity model was additionally applied, revealing an even more accurate description across the whole temperature range. Next to viscosity, TEMPUS measurements allow the determination of surface tension. With a value of 0.9 N m−1, it is significantly lower than that of other Zr-based metallic glasses without the element sulfur.

Changes in the crystallization sequence upon sulfur addition in the Zr52.5Cu17.9Ni14.6Al10Ti5 bulk metallic glass-forming liquid revealed by in situ high-energy x-ray diffraction

Bulk metallic glasses (BMGs) surpass the strength of steels and possess the elasticity and formability of polymers. The key to obtain these properties is to conserve the amorphous structure of a metallic melt and avoid crystallization during processing. In this work, a change in the crystallization sequence in the widely used BMG ${\mathrm{Zr}}_{52.5}{\mathrm{Cu}}_{17.9}{\mathrm{Ni}}_{14.6}{\mathrm{Al}}_{10}{\mathrm{Ti}}_{5}$ (Vit105) upon the addition of sulfur (${\mathrm{Zr}}_{51.45}{\mathrm{Cu}}_{17.54}{\mathrm{Ni}}_{14.31}{\mathrm{Al}}_{9.8}{\mathrm{Ti}}_{4.9}{\mathrm{S}}_{2}$; Vit105 ${\mathrm{S}}_{2}$) is revealed by in situ high-energy x-ray diffraction, both upon heating from the glassy state and upon cooling from the liquid state during electrostatic levitation. This methodology proves to be a powerful tool to elucidate the complete crystallization behavior of complex BMG-forming liquids. The experiments show that the addition of sulfur changes the crystallization sequence and phases in a different manner upon cooling from the liquid state than upon heating from the glassy state. The thermal stability at low temperatures upon heating is increased, as the supercooled liquid region is extended from 60 to 77 K and the glass transition temperature increases from 671 to 692 K. However, the thermal stability is decreased upon cooling, causing a reduced glass-forming ability.

Indications for a fragile-to-strong transition in the high- and low-temperature viscosity of the Fe43Cr16Mo16C15B10 bulk metallic glass-forming alloy

Viscosity of the Fe-based bulk metallic glass-forming liquid Fe43Cr16Mo16C15B10 is measured around the glass transition and in the stable liquid. Low-temperature measurements are conducted using three-point beam bending in a thermomechanical analyzer, and high-temperature data are obtained from the damping behavior of an oscillating droplet which is electromagnetically levitated in microgravity on a reduced-gravity aircraft. The alloy displays an intermediately strong liquid behavior (D* = 15.1) at low temperatures and a fragile behavior (D* = 7.9) at high temperatures. Hence, the temperature dependence of viscosity changes drastically between the high- and the low-temperature regime, which suggests the existence of a fragile-to-strong liquid-liquid transition in the supercooled liquid. Furthermore, viscosity and fragility data are discussed with respect to the glass-forming ability of the alloy.

Onset of Cooperative Dynamics in an Equilibrium Glass-Forming Metallic Liquid.

Onset of cooperative dynamics has been observed in many molecular liquids, colloids, and granular materials in the metastable regime on approaching their respective glass or jamming transition points, and is considered to play a significant role in the emergence of the slow dynamics. However, the nature of such dynamical cooperativity remains elusive in multicomponent metallic liquids characterized by complex many-body interactions and high mixing entropy. Herein, we report evidence of onset of cooperative dynamics in an equilibrium glass-forming metallic liquid (LM601: Zr51Cu36Ni4Al9). This is revealed by deviation of the mean effective diffusion coefficient from its high-temperature Arrhenius behavior below TA ≈ 1300 K, i.e., a crossover from uncorrelated dynamics above TA to landscape-influenced correlated dynamics below TA. Furthermore, the onset/crossover temperature TA in such a multicomponent bulk metallic glass-forming liquid is observed at approximately twice of its calorimetric glass transition temperature (Tg ≈ 697 K) and in its stable liquid phase, unlike many molecular liquids.

Coincidence of collective relaxation anomaly and specific heat peak in a bulk metallic glass-forming liquid

The study of relaxational behavior of multicomponent metallic liquids still holds the key to understanding and improving the glass-forming abilities of bulk metallic glasses. Herein, we report measurements of the collective relaxation times in a melted bulk metallic glass $(\mathrm{LM}601{\mathrm{Zr}}_{51}{\mathrm{Cu}}_{36}{\mathrm{Ni}}_{4}{\mathrm{Al}}_{9})$ in the kinetic regime $(Q$: $1.5--4.0{\AA{}}^{\ensuremath{-}1})$ using quasielastic neutron scattering. The results reveal an unusual slope change in the Angell plots of the collective relaxation time of this metallic liquid around $950{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$, beyond the melting point of the material. Specific heat capacity measurement also reveals the presence of a peak around the same temperature. The coincidence is rationalized using Adams-Gibbs theory, and motivates more careful experimental and computational studies of the metallic liquids in the future.

Thermodynamics and structural relaxation in Ce-based bulk metallic glass-forming liquids

Thermodynamics, kinetics and structural relaxation of Ce-based bulk metallic glass-forming liquid were investigated in the glass transition region by calorimetric measurements. The differences in thermodynamic functions were calculated between the supercooled liquid and crystalline state of the Ce-based alloys. Structural relaxation was studied by heating rate dependence of glass transition temperature. In terms of fragility parameter m, the Ce-based alloys were stronger liquid than other metallic glass-forming liquids. The correlation of the excellent glass-forming ability of Ce-based alloys with the thermodynamic property (Gibbs free energy) and the kinetic property ( m) was discussed. The structural relaxation from glass state to the equilibrium supercooled state was well described by Tool–Narayanaswamy–Moynihan (TNM) model using the parameters derived from the calorimetric measurements.

Viscosities of the Zr-based bulk metallic glass-forming liquids

We have discussed the glass transition and the viscosity of supercooled metallic liquids, by using the replica symmetry breaking and the gauge-invariant formula. We have analyzed the viscosity data points of the Zr-based bulk metallic glass-forming liquid with the present model.

The slow β-relaxation observed in Ce-based bulk metallic glass-forming supercooled liquid

Dynamic mechanical relaxation measurements are performed on a Ce-based metallic supercooled liquid close to its glass transition temperature T g. An obvious excess wing is observed both in the temperature and frequency dependent loss modulus curves by the calculation the relaxation time of the α-relaxation in supercooled liquid with the fit by the combination of the Kohlrausch–Williams–Watts and Vogel–Fulcher–Tamman equation. The results indicate that the slow β-relaxation process exists in the metallic liquid and arises from the small-scale translational motions of atoms that are linked in its metastable islands.

Strain Rate Induced Crystallization in Bulk Metallic Glass-Forming Liquid

We report on the solidification of Au49, Ag5.5, Pd2.3, Cu26.9, Si16.3 bulk metallic glass under various strain rates. Using a copper mold casting technique with a low strain rate during solidification, this alloy is capable of forming glassy rods of at least 5 mm in diameter. Surprisingly, when the liquid alloy is splat cooled at much higher cooling rates and large strain rates, the solidified alloy is no longer fully amorphous. Our finding suggests that the large strain rate during splat cooling induces crystallization. The pronounced difference in crystallization behavior cannot be explained by the previously observed strain rate effect on viscosity alone. A strain rate induced phase separation process is suggested as one of the explanations for this crystallization behavior. The strain-rate-dependent critical cooling rate must be considered in order to assess the intrinsic glass forming ability of metallic liquid.

Viscous flow of the Pd43Ni10Cu27P20 bulk metallic glass-forming liquid

The equilibrium viscosity of the Pd43Ni10Cu27P20 bulk metallic glass-forming liquid was measured over a wide temperature range from the equilibrium supercooled liquid state to the glass transition region using parallel-plate rheometry and three-point beam bending. Based on the measured viscosity data, the fragility of this liquid was quantitatively determined. The Pd43Ni10Cu27P20 alloy, despite exhibiting the best glass-forming ability reported thus far, is relatively fragile compared with other bulk glass-forming liquids, such as Vit 1 and Vit 4.

Thermodynamics, enthalpy relaxation and fragility of the bulk metallic glass-forming liquid Pd 43Ni 10Cu 27P 20

Thermodynamic properties, enthalpy relaxation and fragility of a Pd 43Ni 10Cu 27P 20 bulk metallic glass-forming liquid have been investigated and the thermodynamic functions been calculated. The enthalpy relaxation from the amorphous state into the equilibrium supercooled liquid state was found to follow a stretched exponential function with the relaxation time obeying an Arrhenius law. The fragility index, calculated from the heating rate dependence of T g, yields a value of 65. The excellent glass-forming ability of this alloy is attributed to a smaller thermodynamic driving force and larger diffusion length for crystallization than in other bulk metallic glass-forming alloys.

Pronounced asymmetry in the crystallization behavior during constant heating and cooling of a bulk metallic glass-forming liquid

The crystallization behavior of the supercooled bulk metallic glass-forming Zr41Ti14Cu12Ni10Be23 liquid was studied with different heating and cooling rates. A rate of about 1 K/s is sufficient to suppress crystallization of the melt upon cooling from the equilibrium liquid. Upon heating, in contrast, a rate of about 200 K/s is necessary to avoid crystallization. The difference between the critical heating and cooling rate is discussed with respect to diffusion-limited growth taking classical nucleation into account. The calculated asymmetry of the critical heating and cooling rate can be explained by the fact that nuclei formed during cooling and heating are exposed to different growth rates.

Equilibrium viscosity of the Zr 41.2Ti 13.8Cu 12.5Ni 10Be 22.5 bulk metallic glass-forming liquid and viscous flow during relaxation, phase separation, and primary crystallization

The flow behavior of the supercooled Zr 41.2Ti 13.8Cu 12.5Ni 10Be 22.5 bulk metallic glass-forming liquid is studied in isothermal three-point beam-bending experiments. The experiments lead to the determination of the equilibrium viscosity as a function of temperature. Comparison with other glass-forming liquids shows that the Zr 41.2Ti 13.8Cu 12.5Ni 10Be 22.5 alloy is a strong liquid, similar to sodium silicate liquids. Flow measurements during phase separation and subsequent formation of crystals embedded in a non-crystalline matrix reveal a dramatic slowdown of the kinetics of the matrix that is expressed in an increase of the viscosity by several orders of magnitude.