Crystallization Of Metallic Glass Research Articles

Crystallization of Metallic Glasses and Supercooled Liquids.

This is an overview of recent findings on the structural changes observed upon heating, including crystallization processes in conventional metallic glasses, bulk metallic glasses, and their corresponding supercooled liquids. This paper encapsulates the various crystallization behaviors in metallic glasses by primary, eutectic, and polymorphous mechanisms, highlighting the complexity and diversity of the nucleation and growth mechanisms involved. Mechanically induced room-temperature crystallization is also discussed.

Effect of strain rate and temperature on dynamic compressive behavior of HfBeTiZrCuNi high entropy bulk metallic glass

This study investigated the high-temperature dynamic mechanical properties of Hf-based high entropy bulk metallic glass (HE-BMG). Uniaxial dynamic compressive tests of Hf-based HE-BMG were conducted at elevated temperatures (from 298 to 800 K) under a high strain rate (from 1000 to 5000 s−1) by a split Hopkinson pressure bar (SHPB) device with a high-temperature system, and the failed specimens were analyzed in terms of microstructures and fracture modes. The dynamic test results show that the maximum compressive stress and the total strain decrease with increasing strain rate and temperature, exhibiting significant strain rate and temperature sensitivity. Three different fracture modes were observed with increasing strain rates, while heating the temperature could promote the transition process of the fracture modes. When the adiabatic or heating temperature reaches above the crystallization temperature, the embrittlement caused by metallic glass crystallization makes the fracture mode change. The mechanical behavior of Hf-based HE-BMG at high temperatures and high strain rates could be attributed to the combination of adiabatic heating and embrittlement.

Impact of Shadow Glass Transition on Crystallization in Metallic Glass

Impact of Shadow Glass Transition on Crystallization in Metallic Glass

Effect of annealing at Tg on the crystallization behaviors of Au49Ag5.5Pd2.3Cu26.9Si16.3 metallic glass revealed by nanocalorimetry

Crystallization of metallic glass is not only affected by undercooling but also influenced by microstructure. However, the role of structure in the crystallization is still ambiguous. In this study, nanocalorimetry with a rapid quenching rate was used to obtain the critical cooling rates suppressing nucleation and crystal growth, realizing the in-situ preparation of the amorphous phase. Based on the nuclei-free metallic glass, annealing at Tg was performed to tune the microstructure. With a reheating analysis, the consecutive occurrence of relaxation, nucleation, and crystal growth during annealing was distinguished based on the evolution of crystallization heat. Moreover, the effect of annealing and the resulting microstructure evolution on the reheating crystallization was demonstrated. With the formation of nuclei, the stability of the undercooled melt deteriorated, causing the reduction of activation energy (Ea). When crystals formed during annealing, the confined residual amorphous phase was dominant for crystallization, and a higher Ea was observed.

Revealing bulk metallic glass crystallization kinetics during laser powder bed fusion by a combination of experimental and numerical methods

Laser powder bed fusion (PBF-LB/M) has been used to fabricate bulk metallic glass (BMG) parts. However, there is still a lack of understanding about the crystallization behavior of BMGs during PBF-LB/M. This article aims to combine experimental and numerical methods to gain a more comprehensive understanding of the BMG crystallization kinetics during PBF-LB/M. The material used in this work is an industrial-grade BMG commercially known as AMZ4 (Zr59.3Cu28.8Al10.4Nb1.5, at.%). The samples prepared by PBF-LB/M were characterized by optical microscopy, scanning electron microscopy, and nanoindentation. Simulations were performed using our in-house developed software with setups mimicking the PBF-LB/M experiment. The experimental and numerical results are compared and discussed in detail. The most important finding is that BMG crystallization in PBF-LB/M is a very localized phenomenon, mainly caused by short-range in situ heat treatment. Here, short-range in-situ heat treatment refers to concomitant heat treatment that occurs during the processing of the current melt line, very few subsequent melt lines, and very few subsequent layers. This work provides insight into the BMG crystallization phenomenon that occurs during PBF-LB/M processing, especially its underlying crystallization kinetics. Furthermore, this work demonstrates the usefulness of our in-house developed simulation software in guiding PBF-LB/M process development for BMGs and BMG composites.

How to control the crystallization of metallic glasses during laser powder bed fusion? Towards part-specific 3D printing of in situ composites

How to control the crystallization of metallic glasses during laser powder bed fusion? Towards part-specific 3D printing of in situ composites

Crystal nucleation in Au49Ag5.5Pd2.3Cu26.9Si16.3 glass and undercooled melt

Crystal nucleation is an indispensable step in the crystallization of metallic glasses. With the increase of undercooling, different nucleation kinetics from that predicted by the classical nucleation theory (CNT) could be revealed. A prerequisite to addressing the nucleation kinetics is building a well-identified amorphous structure, which is yet arduous. Moreover, due to the limited temporal and spatial resolution of the conventional experimental methods, nucleation during the crystallization of metallic glass cannot be well recognized. In this study, nanocalorimetry with ultrahigh sensitivity and ultrafast scanning rate is used to address the nucleation kinetics in glass and undercooled melt. With the increase in cooling rate, crystallization, homogeneous nucleation, and heterogeneous nucleation are successively distinguished. Accordingly, the critical cooling rates suppressing crystallization and nucleation are estimated, based on which a well-identified amorphous phase for nucleation studies is produced. By applying Tammann’s two-stage crystal nuclei development method, nucleation in glass and undercooled melt is investigated. According to the evolution of crystallization heat and overall heat on the reheating after the annealing, the underlying kinetic mechanism is revealed with the Johnson-Mehl-Avrami (JMA) method. The nucleation half-time indicates that homogeneous nucleation is dominant for the crystallization below Tg. For the annealing at and above Tg, crystallization completes by the inevitable heterogeneous nucleation followed by crystal growth.

Predictive simulation of bulk metallic glass crystallization during laser powder bed fusion

Laser powder bed fusion (L-PBF) has been employed to fabricate bulk metallic glass (BMG) parts. However, traditional experimental trial-and-error methods to determine process parameters for specific materials and L-PBF machines are time-consuming and expensive. In this paper, a phenomenological crystallization model, namely the Nakamura model, is coupled with L-PBF process simulation. A convenient approach for the crystallization parameter determination and a two-step Euler method for the numerical implementation has been developed. Numerical simulations are performed using the material parameters of a Zr-based BMG Zr59.3Cu28.8Al10.4Nb1.5 (at.%, trade name: AMZ4). The numerical results are validated by comparing with experimental results from different perspectives. Based on the numerical findings, a comprehensive understanding of BMG crystallization behavior during L-PBF is gained. In the end, the crystallization model is implemented in our in-house developed software SAMPLE2D. SAMPLE2D simulation results are presented, whereby the L-PBF process window for fully amorphous AMZ4 parts is explored. Thereby, it is believed that the developed numerical software can be applied to aid process development for BMGs by taking the crystallization phenomenon into account.

How to Control the Crystallization of Metallic Glasses During Laser Powder Bed Fusion? Towards Part-Specific 3d Printing of in Situ Composites

How to Control the Crystallization of Metallic Glasses During Laser Powder Bed Fusion? Towards Part-Specific 3d Printing of in Situ Composites

Evaluation of the Effect of Minor Additions in the Crystallization Path of [(Fe0.5Co0.5)0.75B0.2Si0.05]100-xMx Metallic Glasses by Means of Mössbauer Spectroscopy

Understanding the crystallization of metallic glasses is fundamental in the design of new alloys with enhanced properties and better glass-formability. The crystallization of a series of Fe-based metallic glasses of composition [(Fe0.5Co0.5)0.75B0.2Si0.05]100-xMx (M = Mo, Nb and Zr) has been studied by means of differential scanning calorimetry and transmission Mössbauer spectroscopy. This latter technique allows the following of the microstructural evolution of the studied alloys through the identification and quantification of the several Fe-containing crystalline phases and also through the changes in the amorphous structure at the initial stages of crystallization. The results show that the crystallization products are the same for all the studied compositions (α-Fe, Fe2B, (FeCo)23B6 and a paramagnetic remnant) although with different relative proportions and the crystallization of a phase without Fe in the alloys with Zr. Moreover, the addition of Zr favors the crystallization of α-Fe causing a detrimental effect on the glass forming ability, while the increase in Mo content up to 6 at% favors the crystallization of (FeCo)23B6. The different amount of α-Fe and borides is presented as a measure of the glass forming ability of this type of alloys.

Investigation on the mechanically-induced nanocrystallization in metallic glasses

Shear-induced nanocrystallization in bent ribbons of Pd40Cu30Ni10P20 metallic glass has been quantitatively investigated via synchrotron radiation. The formed nanocrystals volume fraction during deformation has been directly estimated from X-ray diffraction spectra using peaks area integration. The nanocrystallization process during deformation was found to be strongly linked with the microstructure configuration of shear bands in amorphous alloys. A constitutive model based on free volume approach has been introduced to describe the kinetic of mechanically induced nanocrystallization. The solution of the coupled constitutive equations of the model, fitted to experimental data, permits to determine the physical and mechanical parameters governing the phenomena of shear-induced crystallization in metallic glasses.

Heat Effects Occurring in the Supercooled Liquid State and Upon Crystallization of Metallic Glasses as a Result of Thermally Activated Evolution of Their Defect Systems

We show that the kinetics of endothermal and exothermal effects occurring in the supercooled liquid state and upon crystallization of metallic glasses can be well reproduced using temperature dependences of their shear moduli. It is argued that the interrelation between the heat effects and shear modulus relaxation reflects thermally activated evolution of interstitial-type defect system inherited from the maternal melt.

Tracing intermediate phases during crystallization in a Ni–Zr metallic glass

Crystallization of metallic glasses (MGs) is a complex dynamic process, driven by thermodynamics and limited by kinetics, which often involves phase transformation from the metastable amorphous state, via intermediates, to the final stable crystalline states. The intermediate structural state remains mysterious at present but crucial for a deeper understanding of the physics and mechanisms of the crystallization process. Detailed structural characterization of the complex intermediate crystalline phases using transmission electron microscopy (TEM) provides a unique platform to study such issues. Here, we monitor the evolution of the crystallization process for Ni65Zr35 (at%) MG ribbon with structural heterogeneities. Direct visualization combined with compositional analysis reveal that the intermediate phase with Zr concentration higher than that of the MG consists of stacked nanometer-sized layers of Ni-rich units (Ni at% > 67%) and Ni10Zr7-like units, where the thin Ni-rich single layer gradually disappears with increasing annealing temperature. Our findings provide insight into the key role of Ni in the structural transition process, improving the understanding of the atomic diffusion-dominated crystallization in MGs.

Soft magnetic amorphous alloys in X-ray light: Insights from ultra-fast Joule heating experiments

In this contribution a novel setup for studying rapid crystallization of metallic glasses using a time resolved in situ X-ray diffraction combined with a direct current fast Joule heating (flash-annealing) is presented. The setup was implemented and successfully tested at the P02.1 beamline of the PETRA III storage ring (DESY Hamburg, Germany). Its potential use is demonstrated by studying rapid crystallization of soft magnetic Fe73.5Cu1Nb3Si15.5B7 (at.%) metallic glass prepared by melt spinning technique. Flash-annealing experiment is realized by bursting 20 rectangular current pulses with a fixed amplitude of 1.5 A and pulse length δ is varied (30, 40 and 50 ms). A single pulse with duration of 30 ms causes temperature to rise to 770 °C with an average heating rate of 4200 K/s. Phase composition of crystallized material consist of major Fe3Si phase and small traces of boride phase Fe23B6. Consecutive pulses result in cyclic thermal expansion of a crystal lattice, which appears fully reversible. Increasing pulse width to 50 ms causes temperature to increase up to 1020 °C with an average heating rate of 5600 K/s. Differentiation of the temperature profile yields exceptionally high value of heating rate 10800 ± 2400 K/s.

Correlated Unique Variation of Electrical Resistivity to Crystallization Behavior of the Zr52.5Cu17.9Ni14.6Al10Ti5 Metallic Glass

Due to the differences between the glass and crystalline phases, crystallization of metallic glass occurs with heat release, volume shrinkage, and electrical resistivity drastic changes. Electrical resistivity of the Zr52.5Cu17.9Ni14.6Al10Ti5 metallic glass during crystallization was investigated under both continuous heating and isothermal annealing. This amorphous alloy exhibits a continuous variation instead of sharp decline when reaches the onset crystallization temperature. This unique variation was found to be related to the formation of a few quasicrystalline phases. The slower phase transformation process of this metallic glass brings lots of grain boundaries, which results in increasing of resistivity at the last stage during isothermal annealing. These results imply that electrical resistivity measurement is a more intuitive approach to investigate structure evolution of metallic glasses.

Approaching the melting temperature: There regimes in the non-isothermal crystallization of Ce68Al10Cu20Co2 bulk metallic glass revealed by nanocalorimetry

Nanocalorimetry is an ideal candidate for revealing the crystallization of metallic glass in a wide temperature range attributing to its ultrafast heating rate and ultrahigh sensitivity. In this study, in situ preparation of Ce68Al10Cu20Co2 (at.%) metallic glass was realized by the nanocalorimetry. By the subsequent reheating at the rates from 500 to 40,000 K/s, the crystallization in a wide temperature range was demonstrated. The crystallization activation energy and Avrami exponent are calculated with the aid of the Kissinger and Johnson-Mehl-Avrami (JMA) equations to reveal the temperature-dependent nucleation and crystal growth behavior in the undercooled liquid, where three crystallization regimes are identified. At low temperature, the crystallization occurs with constant activation energy. In an intermediate temperature range, the crystallization is controlled by crystal growth with a reduction of activation energy. At temperatures approaching Tm, an increased activation energy resulting from the thermodynamic driving force dominates the nucleation-controlled crystallization. This study provides a novel strategy to reveal the crystallization behavior in the undercooled liquid from Tg to Tm and to demonstrate the transition from growth-controlled crystallization to nucleation-controlled one with the decrease of undercooling.

Roles of ion irradiation and thermal annealing in inducing crystallization in metallic glass

We studied the crystallization behavior of metallic glass Ni50Nb10Zr15Ti15Pt7.5Cu2.5 under different ion irradiation and thermal annealing conditions. The results show that although the room temperature ion irradiation would not introduce observable structural defects in metallic glass, the excess free volume induced by ion irradiation would promote the formation of nanocrystals under thermal annealing. Meanwhile, the interstitial atoms induced by high temperature ion irradiation may act as an important role in the enhancement of atomic diffusivity and nanocrystals growth process. Our study shows that the combination of ion irradiation and thermal annealing may help to achieve controllable structural modification of metallic glass.

Flash DSC determination of the delay time for primary crystallization and minor alloying effect in marginal Al-based metallic glasses

The delay time for primary crystallization plays an important role in the understanding of the transport and nucleation behaviors during crystallization in metallic glasses. In this work, a novel method via Flash DSC is demonstrated to measure the delay time for primary crystallization in Al-based metallic glasses. In a typical Al-based metallic glass of Al87Y7Fe6, the delay times were established corresponding to different temperatures. Transmission electron microscopy tests before and after delay time were conducted to further verify the validity of the measured delay time. The effect of a 1 at.% substitution by Cu on the delay time of Al88Y7Fe5 was investigated to determine the effect of minor alloying on the glass formation ability. The significant changes in the primary crystallization temperatures were demonstrated to be directly related to the corresponding changes in the delay time. The results indicate that minor alloying that is designed to increase the delay time is an effective strategy to enhance the glass formation ability.

Fast Activating Persulfate by Crystallization of Fe-Based Metallic Glasses with External Energy

Very recently, crystallization of metallic glasses (MGs) has presented promising properties in the catalytic field. This work has investigated enhanced catalytic performance of crystallized Fe78Si9B13 ribbons for fast activating persulfate (PS) with assistance of UV-vis light and heat. The ribbons were obtained by annealing at 750°C (Fe-A750) and cibacron brilliant yellow 3G-P (BY 3G-P) dye was used as pollutant. The results indicated that UV-vis light had limited capability to enhance PS activation efficiency by crystallized ribbons while the reaction rate using heat at 65°C was 7.5 times higher than at 25°C, suggesting an advanced performance with heat assistance of Fe-A750 ribbons. Activation energy ∆E for Fe-A750 was measured as 44.5 kJ mol-1. In addition, 5 times reusability could be achieved for Fe-A750 ribbons under 45°C without catalytic decay. The surface morphologies of glassy ribbons, as-annealed Fe-A750 ribbons, HCl-treated Fe-A750 ribbons and after-reused Fe-A750 ribbons have also been systematically studied. This work provides a novel clue to promote applicability of novel crystallized ribbons from MGs.

Correlation between parameters of Arrhenius-type temperature dependency for effective diffusivity governing glass crystallization

The methods for estimation of the effective diffusion coefficients, Deff, governing crystallization of metallic glasses are briefly described and the values of pre-exponential factors, D0, and activation energies, Q, of Arrhenius-type temperature dependencies available in the literature for a number of Fe- and Al-based glasses are reported. It has been shown that the relation between logD0–Q characterizing effective diffusivity are well approximated by straight lines similarly to those found for the migration diffusion coefficients in crystalline and amorphous alloys. It has been found that the parameters A and B of the D0 = Aexp(Q/B) correlations for effective diffusivity in Fe- and Al-based glasses essentially differ from those characterizing the migration diffusion in crystalline metals and are closer to the characteristics of impurity diffusivity in metallic glasses. It has been demonstrated that the values of A and B are dependent in the nature of the base element of alloy. The possible mechanism of the effective diffusion at the crystal/glass interfaces is discussed.