Indicator Of Glass-forming Ability Research Articles

Eutectic growth kinetics as an indicator for glass-forming ability

A metallic glass is known to be often formed more easily by cooling of an alloy melt whose composition is near a deep eutectic. However, the eutectic solidification kinetics, which is closely related to the glass-forming ability (GFA), is rarely reported. In this paper, directional solidification of such a glass-forming eutectic alloy (Zr48Cu36Al8Ag8) has been conducted to investigate the eutectic growth kinetics in terms of the evolution of eutectic structure as a function of the growth rate (V). It was found that, at lower growth rates, the alloy solidified in a dual-phase lamellar structure characterized by the lamellar spacing (λ), with Vλ2 being a constant. As V increased up to a critical value of 400 μm/s, λ decreased and eventually diminished (λ→0), where the eutectic transitioned into a glass. This critical growth rate (i.e., Vce) can be interpreted as a result of the competition between the glass formation and the eutectic growth, in which the glass formation sets a kinetic upper limit for the eutectic growth. Moreover, Vλ2 is found to be kinetically equivalent to Vce, which can be used as a GFA indicator and is readily measurable at low growth rates.

Crystallization kinetics of GdYScAlCo high-entropy bulk metallic glass

The thermal stability and non-isothermal crystallization of a new bulk-amorphous high-entropy (HE-BMG) equiatomic GdYScAlCo alloy were studied by differential scanning calorimetry (DSC). The alloy shows a four-stage crystallization process. The kinetic parameters (activation energy (Eα)), the pre-exponential factor (logA) and glass-forming ability indicators (kinetic fragility index, characteristic temperatures) for the GdYScAlCo alloy were obtained. The Eα values obtained by isoconversional methods indicate a nonlinear Arrhenian behaviour and a complex process. The Avrami equation modification proposed by Jeziorny and the multivariate nonlinear regression method were applied on the nonisothermal crystallization. In the case of primary crystallization of the amorphous GdYScAlCo alloy under nonisothermal conditions, the kinetics of the nucleation process is best described by an autocatalytic reaction.

Improving the glass forming ability and plasticity of ZrCuNiAlTi metallic glass by substituting Zr with Sc

The present study reports the effect of substituting Zr with Sc on the glass forming ability (GFA) and mechanical properties of ZrCuNiAlTi bulk metallic glass (BMG). Results showed that Zr 57- x Cu 20 Ni 8 Al 10 Ti 5 Sc x ( x = 0, 1, 2, 3, 4 at%) BMGs had the best GFA at x = 2, and the critical size was 10 mm, which correlated well with the GFA indicator ( T rg and γ ). The large atomic radius of Sc and small Gibbs free energy difference between the supercooled liquid and crystalline solid (Δ G l-c ) caused significant atomic size mismatch and inhibited crystallization during cooling, ultimately improving GFA. Compression test results indicated that the plasticity of the Zr 55 Cu 20 Ni 8 Al 10 Ti 5 Sc 2 BMG increased fivefold (9.1%) relative to that of the Sc-free case, whereas fracture stress was successfully retained at a value of 1815 MPa. The high plastic strain of Zr 55 Cu 20 Ni 8 Al 10 Ti 5 Sc 2 BMG can be attributed to the localized nanocrystallization phenomenon under uniaxial compression and to the high relaxed excess free volume (REFV) in ZrCuNiAlTiSc BMGs. The high REFV prevented the expansion of shear bands, generated secondary shear bands, and finally increased plasticity. • GFA and plasticity are both enhanced by substituting with Sc in ZrCuNiAlTi BMGs. • The smaller ΔGl-c of Sc2 compared with Sc-free BMG results in its high GFA. • Nanocrystalline phenomenon is the main reason for the high plasticity of Sc2 BMG. • The high plasticity of Sc2 alloy is also attributed to its higher REFV than others.

Thermodynamic and kinetic interpretation of the glass-forming ability of Y-containing Cu-Zr-Al bulk metallic glasses

In the present study, the glass-forming ability (GFA) of (Cu50Zr43Al7)100-xYx (x = 0, 2, 4 and 6 at.%) bulk metallic glasses (BMGs) was investigated from thermodynamic and kinetic viewpoints. The amorphous structure of the alloys was confirmed using several techniques including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and differential scanning calorimetry (DSC). The thermal characteristics obtained through DSC and differential thermal analysis (DTA) were employed to establish a correlation between the GFA and thermodynamics/kinetics factors. The (Cu50Zr43Al7)98Y2 BMG has a promising GFA of 15 mm diameter, i.e. a 50% increase in GFA compared to the base alloy. Several GFA indicators (ΔTx, Trg, γ and K) confirm the excellent glass-forming capability of 2 at.% Y-doped BMG. The role of the optimum yttrium content in improving the GFA was scrutinized considering atomic, topological, and thermodynamics concepts. The interpretations imply that Y enhances the GFA through two main ways including promoting a more densely packed atomic configuration and also through scavenging oxygen as an undesirable element in glass-forming systems.

Liquid phase as an indicator of glass-forming ability

For thermodynamics reasons, most liquids crystallize when they are cooled below their liquidus temperature. However, crystallization can be obstructed if the cooling occurs faster than some critical cooling rate (102 −1010 K/s). Under such conditions, it is suggested that atoms are forced to ‘freeze-in’ at their positions [1,2] with some local short-range order, due to the finite nature of diffusion kinetics, i.e. the rigid state that is produced maintains the disordered or amorphous structure of the liquid. In this short-communication, using CALPHAD (CALculation of Phase Diagrams), we ask, can the underlying atomic interactions within the liquid state be a valid measurement of a material's glass-forming ability?

Mechanical properties and crystallization kinetics of Er-containing Cu–Zr–Al bulk metallic glasses with excellent glass forming ability

Investigations were carried out to explore the consequences of Er adding on the glass forming ability (GFA), mechanical properties, and crystallization kinetics of Cu50Zr43Al7 bulk metallic glass (BMG). It is found that the (Cu50Zr43Al7)100-xErx (x = 0, 2, 4, 6 at %) BMGs reflects its best GFA at x = 2 and correlate well with GFA indicator (γ and K) and thermal stability parameter (ΔTx). The Er-containing BMGs showed high compressive strength and Young module in the range of 1816–1890 Mpa and 116–120 GPa, respectively, but no plastic deformation observed in them. The crystallization kinetics lagged with 2 at % Er addition. The large atomic radius of Er and large negative mixing enthalpy of Er with the other constituent elements causes the significant atomic size mismatch and the formation of short-range order in the melt which restrict the long-range diffusion and ordering of atoms that lead to improving GFA and lagging the crystallization kinetics of (Cu50Zr43Al7)98Er2.

Microstructural evolution and properties of laser spot-welded Zr[sbnd]Al[sbnd]Co[sbnd]Ta bulk metallic glass under various initial welding temperatures

To enhance weldability, this study used a Nd:YAG laser (which produces a faster thermal cycle) in combination with a liquid cooling device (LCD) to spot weld (Zr53Al17Co29)99Ta1 BMG. Here, an LCD was employed to provide a variety of initial welding temperatures (IWTs), with progressively lower IWTs from room temperature (RT) to -5 °C. After the welding process, the microstructure evolution (including parent material (PM), heat affected zone (HAZ), and weld fusion zone (WFZ)), glass forming ability (GFA), and mechanical property (microhardness) of the laser-welded samples were investigated.The results showed that two types of crystallines were observed in the HAZ after RT welding. The GFA indicators of the welded samples and microhardness in the HAZ were affected significantly. When the IWT decreased to 0 °C, the crystalline phase in the HAZ and WFZ were barely noticeable which resulted in a softer HAZ; the GFA indicator of the welded sample was not substantially different than that of the PM.

Effect of Ag addition on crystallization kinetics and thermal stability of As–Se chalcogenide glasses

Chalcogenide glasses of (As50Se50)100−xAgx (0 ≤ x ≤ 25) were prepared using the melt quenching technique under non-isothermal conditions. Differential scanning calorimetry curves measured at different heating rates (5 ≤ β ≤ 40 K min−1) are used to characterize the as-quenched samples. The thermal stability was monitored through the calculation of the temperature difference T c − T g, stability parameter S and crystallization rate factor K p. The glass-forming ability (GFA) was investigated on the basis of Hurby parameter H r which is a strong indicator of GFA. In addition, the activation energy of glass transition E t, activation energy of crystallization E c and Avrami exponent n of the studied compositions were determined. The mechanism of crystallization was found to be a combination of two- and three-dimensional crystal growth.

Free volume: An indicator of the glass-forming ability in binary alloys

As a specific concept, free volume is proposed to affect the glass formation in alloys, while such issue remains unsolved, because free volume itself is ambiguous and elusive. In this work, the correlation between the free volume and the glass-forming ability (GFA) in some binary alloy systems has been investigated by a series of simulations combined with synchrotron-radiation based experiments. A new approach for detecting void spaces and even free volumes quantitatively in metallic glasses is developed, based on which we reveal that the size of free volumes significantly affects the glass formation. In particular, for ribbons with different compositions but the same thickness, a composition where there is a local maximum of GFA, there is a local bump of size value of free volumes, making it possible for free volumes to be an effective indicator of GFA. The present work provides new insight into the glass formation from free volume aspect, which can be helpful for understanding of both structure and properties in metallic glasses.

Mechanical and Magnetic Properties of New (Fe,Co,Ni)–B–Si–Ta Bulk Glassy Alloys

The alloying effects of the like-atom substitution of Ni and Co for Fe on the various properties of Fe70B16.7Si8.3Ta5 metallic glass are investigated in this present work. New Fe-based bulk glassy alloys, namely Fe60–x Co x Ni10B16.7Si8.3Ta5 (at.%; x = 10, 20 and 30) with critical diameters up to 1.5 mm, were made by means of copper mold casting. A new glass-forming ability indicator, viz., the enthalpy of supercooled liquid, has been introduced for assessment of the glass-forming abilities (GFAs) of these Fe-based multi-component alloys. Nano-indentation results indicate that the calculated elastic modulus and hardness of the bulk glassy alloys are lower than those of the Fe70B16.7Si8.3Ta5 alloy. Among these bulk glassy alloys, Fe70B16.7Si8.3Ta5 exhibits the large elastic modulus and hardness with values of 178 ± 1 GPa and 12.9 ± 0.1 GPa, respectively. All the bulk glassy alloys exhibit good soft magnetic properties with high saturation magnetization B s ~ 0.75–1.04 T but low coercive force H c ~ 0.2–5.2 A/m.

Evolution of glass forming ability indicator by genetic programming

A symbolic regression technique has been employed to evolve the functional relationship among the characteristic transformation temperatures, viz. glass transition temperature (Tg), onset crystallization temperature (Tx) and offset temperature of melting (Tl) concerning glass forming ability (GFA) of bulk metallic glasses (BMGs). The critical diameters (Dmax) of 410 reported BMGs, along with their Tg, Tx and Tl values, forms the training data, for a genetic programming based computer code which attempts to evolve an expression leading to high correlation with Dmax as the target variable. Another set of recently reported 184BMGs data, is used to assess the performance of the evolved expression. The evolved expression shows significantly improved correlations with critical diameter Dmax, for training data, test data and training and test data considered together. The same also compares well with the high correlation GFA indicators reported earlier in the literature.

Relation of Structure, Composition and Glass Forming Ability in Zr-Cu Binary Amorphous Alloys

Molecular dynamics simulation was used to simulate Zr-Cu binary system, in which the relationship between structure, composition and glass forming ability was study. Atomic local structures were analyzed from view of chemical and topological short range order. Reduction fraction of full icosahedra ( B c ) was developed to establish the relation of structure-composition and glass forming ability(GFA) in Zr-Cu binary system. Obviously peaks were observed at some certain compositions which own the good GFA. As a structure factor, B c could be a indicator of GFA of Zr-Cu alloys. Our works contributed to further understanding the effect of atomic structures on glass forming.

Composition formulas of Fe–B binary amorphous alloys

Fe–B binary alloys constitute the basis of many Fe-based metallic glasses with superior glass forming abilities and soft magnetic properties. The present work is devoted to understanding the composition rule of Fe–B binary amorphous alloys using the cluster-plus-glue-atom model and the relevant composition formula theory. According to this model, an ideal metallic glass is based on a chemical building block composed of a first-neighbor coordination polyhedral cluster plus one or three glue atoms, and the total number of valence electrons per unit formula is close to 24. For the Fe–B system, the principal cluster [B–B2Fe8], which enters into the composition formula for metallic glasses, is derived from the eutectic phase BFe2 (Al2Cu-type). This cluster, after being glued with one Fe atom, produces a cluster formula [B–B2Fe8]FeB3Fe9Fe75B25 that presents nearly 24 valence electrons. Experimental verification was then carried out, and at the anticipated composition, the crystallization temperature and glass-forming ability indicator α was the highest, indicating the best thermal stability and glass-forming ability. The crystallization behavior and structure characteristics of Fe–B binary amorphous alloys were also discussed.

Investigating the atomic level influencing factors of glass forming ability in NiAl and CuZr metallic glasses.

Bulk metallic glasses are a relatively new class of amorphous metal alloy which possess unique mechanical and magnetic properties. The specific concentrations and combinations of alloy elements needed to prevent crystallization during melt quenching remains poorly understood. A correlation between atomic properties that can explain some of the previously identified glass forming ability (GFA) anomalies of the NiAl and CuZr systems has been identified, with these findings likely extensible to other transition metal-transition metal and transition metal-metalloid (TM-M) alloy classes as a whole. In this work, molecular dynamics simulation methods are utilized to study thermodynamic, kinetic, and structural properties of equiatomic CuZr and NiAl metallic glasses in an attempt to further understand the underlying connections between glass forming ability, nature of atomic level bonding, short and medium range ordering, and the evolution of structure and relaxation properties in the disordered phase. The anomalous breakdown of the fragility parameter as a useful GFA indicator in TM-M alloy systems is addressed through an in-depth investigation of bulk stiffness properties and the evolution of (pseudo)Gruneisen parameters over the quench domain, with the efficacy of other common glass forming ability indicators similarly being analyzed through direct computation in respective CuZr and NiAl systems. Comparison of fractional liquid-crystal density differences in the two systems revealed 2-3 times higher values for the NiAl system, providing further support for its efficacy as a general purpose GFA indicator.

Relation of various GFA indicators to the critical diameter of Zr-based BMGs

In the face of a large number of glass forming ability (GFA) thermal indicators that can be found in the literature, the authors have made an attempt to order a variety of them by their correlation with the critical diameters (Dc) of four various Zr-based alloys. Dcs were determined by the wedge test and varied from 4.5 to 10.4mm. Characteristic temperatures, determined by the DTA, were used to calculate some GFA thermal indicators: ΔTxg, Trg, Kgl, α, β1, β2, γ, γm, δ and ξ. The data were used to built plots: GFA indicator versus Dc. Using the logarithmic fitting, the R2 correlation coefficient was determined for each indicator. Ordering the GFA indicators by the R2 ascending values allowed both qualitative as well as quantitative comparisons. It was revealed that the ΔTxg indicator exhibited weak correlation (R2=0.019) with the Dc in contrast to β1, γ, γm and ξ. It was also proven that the solidus temperature should not be used in a formula of a GFA indicator in order to achieve high correlation with the Dc.The authors also made an attempt to modify the formula of the γm indicator in order to improve the R2 value. It was possible to raise it to the level of 0.882 – a new GFA indicator ω was proposed.

Signature of properties in elastic constants of no-metalloid bulk metallic glasses

The relations between properties and elastic constants of no-metalloid bulk metallic glasses (BMGs) were investigated. The specific volume (Vm)-normalized characteristic temperatures and mechanical properties of the BMGs reveal solid linear relations with elastic constants, in particular, exceptionally well with the Young's modulus (E). Since Vm becomes known through the “rule of mixture” for no-metalloid BMGs, the characteristic temperatures and, in turn, the glass-forming ability (GFA), thermal stability and mechanical properties (yielding strength, yielding shear stress and fracture strength) can be estimated through E. The values of characteristic temperatures and two GFA indicators (the reduced glass transition temperature and parameter gama (γ)) calculated by these statistical relations agree fairly well with the experimental data. A five-step strategy for designing metalloid-free BMGs with predictable properties was then worked out. The extracted clue of E and Vm to properties of BMGs makes it possible to efficiently design and screen metallic glass formers with desired properties, and provides an insight into the understanding of the nature of the glass formation and the disordered structure–properties relationship.

Effect of the Germanium on the Crystallization Kinetics of Se-Te Glassy Alloy

Differential Thermal Analysis (DTA) has been employed to investigate the glass transition activation energy Et , thermal stability and glass forming ability (GFA) of (Se80Te20)100-xGex (x = 0, 2, 4, 6) chalcogenide glasses. The DTA curves of the composition under investigation were recorded at the different heating rates. From the dependence of glass transition temperature on heating rate, the Et has been calculated on the basis of the Kissinger model. Thermal stability has been monitored through the calculation of temperature differences Tc-Tg and the stability parameter S. The GFA has been investigated on the basis of Hruby parameter Hr , which is a strong indicator of GFA.

Statistical composition-structure-property correlation and glass-forming ability based on the full icosahedra in Cu–Zr metallic glasses

Using the large-scale atomic/molecular massively parallel simulator, fraction of the Cu-centered ⟨0,0,12,0⟩ full icosahedra (fico) is obtained from a statistical analysis over a broad compositional range with high resolution in the Cu–Zr binary system. Weak but significant peaks are observed at certain compositions which coincide with good glass formers. This correlation implies that the change in fico is a fundamental structural factor in determining the ease of glass formation. In this regard, fico can be an indicator of glass-forming ability. Our work provides further understanding on the atomic structure of the Cu–Zr system and its effect on glass formation.

Copper oxide content dependence of crystallization behavior, glass forming ability, glass stability and fragility of lithium borate glasses

Abstract Differential thermal analysis (DTA) and X-ray diffraction (XRD) have been employed to investigate the copper oxide content dependence of the glass transition temperatures data, activation energy for the glass transition E t , glass stability GS, fragility index Fi, the glass-forming ability (GFA) and crystallization behavior of {(100− x ) mol% Li 2 B 4 O 7 – x mol% CuO} glass samples, where x =0–40 mol% CuO. From the dependence of the glass transition temperature T g on the heating rate β , the fragility, F i , and the activation energy, E t , have been calculated. It is seen that F i and E t are attained their minimum values at 0 x ≤ 15 mol % of CuO. The addition of CuO above 15 mol% causes a decrease in the glass-forming ability and the supercooled liquid region SCL. Thermal stability has been monitored through the calculation of the temperature difference T x – T g , SCL region and the GS. The GFA has been investigated on the basis of Hruby parameter K H , which is a strong indicator of GFA, and the relaxation time. Results of GFA are in good agreement with the fragility index, F i , calculations indicating that {90Li 2 B 4 O 7 ·10CuO} is the best glass former. The stronger glass forming ability has decreasing the fragility index. XRD result indicates that no fully amorphous samples but a mixture of crystalline and amorphous phases are formed in the samples containing x >25 mol% CuO and below it composed of glassy phase. Increasing the CuO content above 25 mol% helps the crystallization process, and thus promotes a distinct SCL region. XRD suggests the presence of micro-crystallites of remaining residual amorphous matrix by increasing the CuO content.

Simulation of reduced glass transition temperature of Cu–Zr alloys by molecular dynamics

Estimation of glass forming ability (GFA) of alloys by simulation before experimental trial and errors has long been a tempting pursuit in exploration of bulk metallic glasses. Reduced glass transition temperature (Trg) of CuxZr100−x alloys (x=46, 50, 62) were simulated by molecular dynamics using tight-binding potentials. Glass transition temperature (Tg) and melting temperature (Tm) of each alloy were calculated separately to obtain Trg (=Tg/Tm) as an indicator of GFA. It is shown that the calculated Tg and Trg values of CuxZr100−x alloys are in agreement with experimental data within 2%–8%, and 5%–11%, respectively. Simulation as such provides a possibility to preliminarily sort out alloys worthy of experimental trials.