skip to main content

Title: Combinatorial measurement of critical cooling rates in aluminum-base metallic glass forming alloys

Direct measurement of critical cooling rates has been challenging and only determined for a minute fraction of the reported metallic glass forming alloys. Here, we report a method that directly measures critical cooling rate of thin film metallic glass forming alloys in a combinatorial fashion. Based on a universal heating architecture using indirect laser heating and a microstructure analysis this method offers itself as a rapid screening technique to quantify glass forming ability. We use this method to identify glass forming alloys and study the composition effect on the critical cooling rate in the Al–Ni–Ge system where we identified Al51Ge35Ni14as the best glass forming composition with a critical cooling rate of 104 K/s.

; ; ; ; ; ; ; ; ; ;
Publication Date:
Journal Name:
Scientific Reports
Nature Publishing Group
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    The viscosity and its temperature dependence, the fragility, are key properties of a liquid. A low fragility is believed to promote the formation of metallic glasses. Yet, the fragility remains poorly understood, since experimental data of its compositional dependence are scarce. Here, we introduce the film inflation method (FIM), which measures the fragility of metallic glass forming liquids across wide ranges of composition and glass-forming ability. We determine the fragility for 170 alloys ranging over 25 at.% in Mg–Cu–Y. Within this alloy system, large fragility variations are observed. Contrary to the general understanding, a low fragility does not correlate with high glass-forming ability here. We introduce crystallization complexity as an additional contribution, which can potentially become significant when modeling glass forming ability over many orders of magnitude.

  2. Abstract

    Mid-infrared spectroscopy is one of the few ways to observe the composition of the terrestrial planet-forming zone, the inner few astronomical units, of protoplanetary disks. The species currently detected in the disk atmosphere, for example, CO, CO2, H2O, and C2H2, are theoretically enough to constrain the C/O ratio on the disk surface. However, thermochemical models have difficulties in reproducing the full array of detected species in the mid-infrared simultaneously. In an effort to get closer to the observed spectra, we have included water UV-shielding as well as more efficient chemical heating into the thermochemical code Dust and Lines. We find that both are required to match the observed emission spectrum. Efficient chemical heating, in addition to traditional heating from UV photons, is necessary to elevate the temperature of the water-emitting layer to match the observed excitation temperature of water. We find that water UV-shielding stops UV photons from reaching deep into the disk, cooling down the lower layers with a higher column. These two effects create a hot emitting layer of water with a column of 1–10 × 1018cm−2. This is only 1%–10% of the water column above the dustτ= 1 surface at mid-infrared wavelengths in the models andmore »represents <1% of the total water column.

    « less
  3. Abstract

    Galactic outflows driven by supernovae (SNe) are thought to be a powerful regulator of a galaxy’s star-forming efficiency. Mass, energy, and metal outflows (ηM,ηE, andηZ, here normalized by the star formation rate, the SNe energy, and metal production rates, respectively) shape galaxy properties by both ejecting gas and metals out of the galaxy and by heating the circumgalactic medium (CGM), preventing future accretion. Traditionally, models have assumed that galaxies self-regulate by ejecting a large fraction of the gas, which enters the interstellar medium (ISM), although whether such high mass loadings agree with observations is still unclear. To better understand how the relative importance of ejective (i.e., high mass loading) versus preventative (i.e., high energy loading) feedback affects the present-day properties of galaxies, we develop a simple gas-regulator model of galaxy evolution, where the stellar mass, ISM, and CGM are modeled as distinct reservoirs which exchange mass, metals, and energy at different rates within a growing halo. Focusing on the halo mass range from 1010to 1012M, we demonstrate that, with reasonable parameter choices, we can reproduce the stellar-to-halo mass relation and the ISM-to-stellar mass relation with low-mass-loaded (ηM∼ 0.1–10) but high-energy-loaded (ηE∼ 0.1–1) winds, with self-regulation occurring primarily through heatingmore »and cooling of the CGM. We show that the model predictions are robust against changes to the mass loading of outflows but are quite sensitive to our choice of the energy loading, preferringηE∼ 1 for the lowest-mass halos and ∼0.1 for Milky Way–like halos.

    « less
  4. Abstract

    MESSENGER observations suggest a magma ocean formed on proto-Mercury, during which evaporation of metals and outgassing of C- and H-bearing volatiles produced an early atmosphere. Atmospheric escape subsequently occurred by plasma heating, photoevaporation, Jeans escape, and photoionization. To quantify atmospheric loss, we combine constraints on the lifetime of surficial melt, melt composition, and atmospheric composition. Consideration of two initial Mercury sizes and four magma ocean compositions determines the atmospheric speciation at a given surface temperature. A coupled interior–atmosphere model determines the cooling rate and therefore the lifetime of surficial melt. Combining the melt lifetime and escape flux calculations provides estimates for the total mass loss from early Mercury. Loss rates by Jeans escape are negligible. Plasma heating and photoionization are limited by homopause diffusion rates of ∼106kg s−1. Loss by photoevaporation depends on the timing of Mercury formation and assumed heating efficiency and ranges from ∼106.6to ∼109.6kg s−1. The material for photoevaporation is sourced from below the homopause and is therefore energy limited rather than diffusion limited. The timescale for efficient interior–atmosphere chemical exchange is less than 10,000 yr. Therefore, escape processes only account for an equivalent loss of less than 2.3 km of crust (0.3% of Mercury’s mass).more »Accordingly, ≤0.02% of the total mass of H2O and Na is lost. Therefore, cumulative loss cannot significantly modify Mercury’s bulk mantle composition during the magma ocean stage. Mercury’s high core:mantle ratio and volatile-rich surface may instead reflect chemical variations in its building blocks resulting from its solar-proximal accretion environment.

    « less
  5. We present mid-IR spectroscopic characterization of the low-phonon chalcogenide glass, Ga2Ge5S13(GGS) doped with Er3+ions. Under the excitation at ∼800 nm, Er3+:GGS exhibited broad mid-IR emission bands centered at ∼2.7, ∼3.5, and ∼4.5 µm at room temperature. The emission lifetime of the4I9/2level of Er3+ions in GGS glass was found to be millisecond-long at room temperature. The measured fluorescence lifetimes were nearly independent of temperature, indicating negligibly small nonradiative decay rate for the4I9/2state, as can be expected for a low-maximum-phonon energy host. The transition line-strengths, radiative lifetimes, fluorescence branching ratios were calculated by using the Judd-Ofelt method. The peak stimulated emission cross-section of the4I9/24I11/2transition of Er3+ion was determined to be ∼0.10×10−20cm2at room temperature.