Reduced Glass Transition Temperature Research Articles

Preparation of Poly(Styrene-co-Acrylonitrile)-Grafted Attapulgite via Simultaneous Reverse and Normal Initiation Atom Transfer Radical Polymerization (SR&NI ATRP) and Its Effect on Polycarbonate/Acrylonitrile-Butadiene-Styrene Terpolymer Ternary Composites

To further improve the comprehensive properties of polycarbonate/acrylonitrile–butadiene–styrene terpolymer blends (PC/ABS), in this work, styrene–acrylonitrile copolymer [P(St-co-An)] was grafted on the surface of attapulgite particles (ATP) by simultaneous reverse and normal initiation ATRP (SR&NI ATRP) to yield ATP@P(St-co-An) hybrid particles. Then a series of PC/ABS/ATP@P(St-co-An) composites were prepared via the melt blending method. The effects of ATP@P(St-co-An) content on the morphological, mechanical, thermal and rheological properties of the composites were investigated in detail. The core-shell ATP@P(St-co-An) hybrid particles with the polymer layer thickness of 20-40 nm were synthesized successfully according to the results of X-ray photoelectron spectrometer (XPS), Fourier transform infrared spectrometer (FTIR), gel permeation chromatography (GPC), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM). The improvement in mechanical properties, reduced glass transition temperature (T g) difference between PC and ABS and micromorphology changes of the composites proved the compatibilization, strengthening, and toughening effect of the ATP@P(St-co-An). Compared with the PC/ABS blend, with strength and toughness of 50.8 MPa and 56.3 kJ/m2, when the ATP@P(St-co-An) content was 4 wt%, a reasonable balance (85.8 MPa and 86.2 kJ/m2) between strength and toughness was achieved with substantially enhanced thermal stability. Moreover, the composite showed more remarkable non-Newtonian behavior, and its processability was also improved. We believe this work provides an effective approach to optimize the compatibility and comprehensive properties of PC/ABS blends.

Accelerated discovery of Magnesium-based amorphous alloys through a property-driven active learning strategy

Magnesium (Mg)-based amorphous alloys hold significant potential for applications in the automotive, aerospace, and biomedical industries. However, they are limited by their smaller size compared to other amorphous alloys. A higher reduced glass transition temperature (Trg) is associated with larger sizes in Mg-based amorphous alloys. Yet, due to the vast chemical space involved, designing Mg-based amorphous alloys with higher Trg using traditional ‘trial and error’ method is a challenging endeavor. In this work, we developed a property-driven active learning strategy to customize Mg-based amorphous alloys with enhanced Trg. After just two iterations, we successfully tailored four amorphous alloys with high Trg values. Under identical experimental conditions, two of these alloys exhibited Trg values surpassing that of Mg0·65Ag0·19Cu0.06Gd0.1, the alloy with best Trg value in the reported references. SHAP analysis revealed that Trg tends to be higher when the Ag atomic ratio exceeds 0.045, the Cu atomic ratio is below 0.18, the Ni atomic ratio is below 0.025, and the Mg atomic ratio is below 0.665. Our work offers a reliable strategy for designing Mg-based amorphous alloys with higher Trg and provides valuable insights for the rational design of these alloys.

Mechanical characteristics of optimized alkali-treated Similax Zelanica/glass fiber/nanosilica composites in an epoxy matrix: An experimental investigation and numerical study

The demand for environmentally conscious materials has led the research on natural fiber composites as an alternative to synthetic materials in various industries. This study focuses on the optimization and preparation of alkali-treated Similax Zelanica/glass fiber and nanosilica-reinforced epoxy composites. The weight % of Similax Zelanica/glass and nanosilica was optimized using the grey relational analysis (GRA) multiparameter optimization technique and DOE of L9 orthogonal was used. Mechanical properties including tensile, flexural, impact, rock well hardness, and dynamic mechanical analysis were evaluated. Results indicate that increasing fiber volume fraction up to 30% enhances mechanical properties, with subsequent declines beyond this threshold. Tensile strength peaked at 30% fiber volume (75 MPa), while flexural strength also peaked at 30% substrate (140 MPa). The impact test showed a maximum of 1.84 kJ/m2 at 30% volume fraction. Maximum hardness of 85 RHN is observed for 30% S and 60% E specimens. Weibull distribution plots results, aligned well with the expected distribution pattern, indicating consistent and reliable mechanical behavior. Water absorption rates increase with fiber volume percentage increase, but optimal alkali treatment improves, absorption resistance to some extent. Dynamic mechanical analysis reveals reduced glass transition temperature Tg (97° C) for composite due to their better interaction nature between fiber/silica nanoparticles and matrix. Further characterization reveals thermal stability (374°C), crystalline properties (crystalline index: 56.87%, crystalline size: 21.23 nm), and functional group composition. Numerical analysis using ANSYS validates experimental results, giving confidence in repeatability. Scanning electron microscope analysis confirms good interfacial bonding, crack propagation details, and absence of impurities in the composite. These results like Mechanical properties, thermal stability, crystalline properties, and functional group composition of the composite confirm its suitability for various applications.

Exploring the role of deep eutectic solvents in enhancing the properties of PMMA for potential electrolyte films

In this study, a novel series of solid PMMA containing deep eutectic solvent (DES) (PMMADES) (Mw = ∼28,374 g mol−1) was successfully synthesized via free radical polymerization of methyl methacrylate (MMA) in different types of DES (e.g., choline chloride (ChCl): 1,2-butanediol (1,2-BD)-DESI, ChCl: 1,3-butanediol (1,3-BD)-DESII, and ChCl: 1,4-butanediol (1,4-BD)-DESIII) in order to overcome the brittleness of commercial PMMA film. Interestingly, flexible PMMADES films with a reduced glass transition temperature (Tg) from 73.36 °C (PMMA) to 55.38 °C were obtained. This is due to the ability of DES to act as a plasticizer by forming interactions with PMMA, as confirmed by FTIR analysis. In addition, the incorporated DES also results in a reduction in the number of crystalline grains, as observed from their optical micrographs. This is due to the increment in amorphous content, as proven by XRD analysis, which shows a reduction in crystallite size from 1.20 nm (PMMA) to 1.12 nm upon the addition of DES. Also, this study found that the PMMADESI system, which involved the incorporation of ChCl: 1,2-BD (DESI), exhibited the highest ionic conductivity (∼10−8 S cm−1) and lowest value of Tg (55.38 °C). This was due to the closest position of the hydroxyl group in 1,2-BD, which contributes to the greater disorderliness and wider ion distribution of the PMMA matrix.

Effect of konjac glucomannan on heat-induced pea protein isolate hydrogels: Evaluation of structure and formation mechanisms

The roles of increasing concentration of konjac glucomannan polysaccharide (KGM) in modifying the thermal, textural, and rheological properties of heat-induced pea protein isolate (PPI) hydrogels at neutral pH and low ionic strength were investigated in this study. Differential scanning calorimetry was first applied to investigate the effect of KGM addition on the thermal properties of pea proteins, finding that an addition of 0.5 % w/v increased the glass transition temperature of pea proteins (from 150 to 154 °C) while on the contrary, higher concentrations of 1.0–1.5 % w/v reduced glass transition temperatures (from 150 °C to ∼ 144 °C). Water holding capacity highlighted that KGM addition significantly increased water retention, reaching values up to 90 % for KGM concentration ≥ 1.0 % w/v. Confocal laser scanning microscopy showed the presence of a phase separation system with increasing concentrations of KGM. Molecular interactions and Fourier transform infrared spectroscopy analysis highlighted that the hydrogels were mainly stabilized by non-covalent intermolecular interactions. Texture analysis confirmed that KGM significantly influenced texture of the hydrogels, in which 1.5 % w/v KGM presented the highest hardness value of 1.34 N. Lastly, small amplitude rotational and oscillatory rheology was employed to evaluate the hydrogels viscosity and viscoelastic properties, which both were significantly increased with increasing KGM concentrations.

Biodegradable Electrospun Conduit with Aligned Fibers Based on Poly(lactic-co-glycolic Acid) (PLGA)/Carbon Nanotubes and Choline Bitartrate Ionic Liquid.

Functionally active aligned fibers are a promising approach to enhance neuro adhesion and guide the extension of neurons for peripheral nerve regeneration. Therefore, the present study developed poly(lactic-co-glycolic acid) (PLGA)-aligned electrospun mats and investigated the synergic effect with carbon nanotubes (CNTs) and Choline Bitartrate ionic liquid (Bio-IL) on PLGA fibers. Morphology, thermal, and mechanical performances were determined as well as the hydrolytic degradation and the cytotoxicity. Results revealed that electrospun mats are composed of highly aligned fibers, and CNTs were aligned and homogeneously distributed into the fibers. Bio-IL changed thermal transition behavior, reduced glass transition temperature (Tg), and favored crystal phase formation. The mechanical properties increased in the presence of CNTs and slightly decreased in the presence of the Bio-IL. The results demonstrated a decrease in the degradation rate in the presence of CNTs, whereas the use of Bio-IL led to an increase in the degradation rate. Cytotoxicity results showed that all the electrospun mats display metabolic activity above 70%, which demonstrates that they are biocompatible. Moreover, superior biocompatibility was observed for the electrospun containing Bio-IL combined with higher amounts of CNTs, showing a high potential to be used in nerve tissue engineering.

Glass Stability and Glass Forming Ability of Ge25−xSe75Sbx (x = 12, 15, and 18) Chalcogenide Glasses Using Thermal Parameters

AbstractIn the present communication glass stability (GS) and glass forming ability (GFA) of Ge25−xSe75Sbx (x = 12, 15, and 18) chalcogenide glasses have been calculated in terms of certain thermal parameters, i.e., reduced glass transition temperature (Trg), Hruby number (H), S‐parameter (S), and ΔT. The glassy samples have been prepared by quenching of melt technique. For structure characterization, XRD technique has been used. For thermal analysis Differential Scanning Calorimetery (DSC) has been used. DSC scans have been recorded at different heating rates, i.e., 5, 10, 15, and 20 K min−1. Stability of glassy samples has also been confirmed in terms of activation energy of glass transition calculated by Kissinger relation. All these parameters indicate that GS and GFA both decrease with increase of Sb content in Ge25−xSe75Sbx (x = 12, 15, and 18) glassy series.

Non-isothermal crystallization kinetics and memory switching properties of Tl-Se-Ge-Sb chalcogenide semiconductor alloy for thermally stable phase change memory applications

Quaternary (Tl20Se70Ge10)0.85Sb0.15 chalcogenide glass was synthesized using melt-quenching and thermal evaporation techniques for bulk and thin film samples, and its amorphous character was confirmed by XRD. Based on different models of non-isothermal crystallization kinetics, the average values of the glass transition and the crystallization activation energies are 121.33 and 82.94 kJ mol−1, respectively. The crystallization mechanism in the examined composition is 2D nucleation growth, according to Avrami exponent Thermal parameters of the studied quaternary glass, like fragility fluctuation free volume reduced glass transition temperature thermal stability and glass formation ability were investigated and indicated that the (Tl20Se70Ge10)0.85Sb0.15 ChG exhibits a good ability of glass formation and thermal stability. The obtained results of the dc electrical conductivity are found to increase with temperature and decrease with film thickness. The electrical conduction activation energy (0.583 ± 0.004 eV) is thickness independent and the predominant conduction mechanism is the hopping of charge carriers in the band tail localized states. The () curves of (Tl20Se70Ge10)0.85Sb0.15 chalcogenide glass film samples were analyzed and shown to be appropriate for a memory switch. The mean value of the threshold voltage decreases exponentially as temperature increases, whereas it increases linearly as film thickness increases. The values of threshold voltage and threshold resistance activation energies are 0.282 ± 0.003 and 0.521 ± 0.004 eV, respectively. The obtained switching characteristics data were discussed in view of the electrothermal model motivated by current channel Joule heating. These findings highlight the suitability of the investigated composition for various optoelectronic applications, such as memory switching devices, optical data storage, phase-change memories and optical fibres sensing devices.

Significantly enhanced crystallization of polylactide Ingeo 4032D by polyethylene ionomer

Poly(lactic acid) (PLA) is the most important biopolymer material due to its excellent biocompatibility, biodegradability, and processability. However, its widespread applications were significantly limited by its low crystallization rate. While adding small molecule organic nucleating agents became a commonly used method in enhancing the crystallization rate, these nucleating agents generally suffer from limited solubility, which caused compromised nucleation efficiency and undesirable product appearance due to their precipitation onto the surface of the PLA products overtime. Here we report an efficient method for improving the PLA crystallization performance by using polyethylene (PE) ionomer as an additive in the PLA/TMC300 (an organic nucleating agent) nucleation/crystallization process. The added ionomer led to enhanced crystallization rate and reduced crystalline grain size. The resulting PLA from crystallization with TMC300 and ionomer showed reduced glass transition temperatures, reduced contact angles, and enhanced elastic modulus without compromising the impact strength and elongation at break. A possible mechanism was proposed for the remarkable synergistic effects of ionomer and TMC-300 in modifying the PLA crystallization process with the ionomer playing the roles of both plasticizer (enhanced PLA chain mobility and crystallization rate) and compatibilizer (enhanced dissolution and dispersion of TMC300 in the PLA matrix). This work offered a promising strategy for crystallization and modification of PLA materials.

Rheology, curing and time‐dependent behavior of epoxy/carbon nanoparticles systems

AbstractThis study delved into the characterization of epoxy nanocomposites containing diglycidyl ether of bisphenol‐A (DGBEA), graphene nanoplates (GN), and carbon nanotubes (CNT) across a range of weight percentages (0.05% to 2%). The nanocomposites were produced through a process involving mechanical stirring and ultrasonication. To assess compatibility, three‐dimensional solubility parameters (3DSP) were employed. CNT demonstrated superior compatibility with epoxy and triethylenetetramine (TETA), due to its higher amount of oxygenated species in nanoparticle surface compared to GN. A rheological percolation phenomenon occurred in CNT systems at concentrations above 0.2%, while GN did not display percolation even at 2% concentration. Incorporating nanoparticles led to increased curing enthalpy due to surface functional groups. As the percolation network formed, viscosity rose, and a reduced glass transition temperature (Tg) indicated restricted molecular mobility. Surprisingly, Tg consistently increased by approximately 27°C during composite annealing, regardless of nanoparticle type or concentration. This was attributed to forming a three‐dimensional network structure potentially originating from reactions between nanoparticle‐oxygenated groups and the epoxy matrix. This phenomenon was crucial in heightened creep and irreversible deformations, setting these nanocomposites apart from pure resin behavior.

Investigations on thermomechanical and structure properties of pure and wet polyimine networks by molecular dynamics simulations

Polyimine polymer is a kind of covalent adaptable networks with excellent reprocessing and self-healing properties. It has attracted wide attentions in recent years because it can release stress by reversible bond exchange reactions without using catalysts. Since polyimines containing -NH- groups are strongly hydrophilic, the influence of water content on their thermomechanical and structure properties is significant. In this study, we establish atomic models involving diamine and dialdehyde monomers combined with triamine cross-linkers to investigate the thermomechanical and structure properties of polyimine networks. Furthermore, different amounts of water molecules are added into networks to explore the interaction between polyimines and water molecules in aqueous polyimine systems. It is concluded that the increase of cross-linking density and conversion degree will improve the thermomechanical properties of polyimines. The water molecules in the aqueous polyimine systems will reduce glass transition temperature and enhance plasticity. Moreover, the diffusion coefficient is found to positively correlate with water content and temperature. Further researches on the structure of polyimines shows that the radius of gyration of polyimines and the radial distribution function of water molecules around the polyimines are also sensitive to temperature and water content. This investigation provides comprehensive information on different factors affecting the thermomechanical properties of pure and wet polyimine networks and contributes toward predicting the evolution of properties of polyimines under different circumstances.

PROPERTIES OF GLASSES IN THE Ag2S–GeS2–As(Sb)2S3 SYSTEMS

The characteristic temperatures for individual glass samples of quasi-ternary systems Ag2S–GeS2–As(Sb)2S3 were determined by differential thermal analysis method. Obtained data show that the glass transition temperature of the alloys is in the range typical of chalcogenide glasses. It was established that the glass transition temperature increases with the modifier content in the range of 402-421 K and 373-438 K for the Ag2S–GeS2–As(Sb)2S3 systems, respectively. For the constant Ag2S concentration, the value of the glass transition and crystallization temperatures increases with the content of germanium (IV) sulfide. The reduced glass transition temperature Tgr was calculated from obtained results which lies in the range of 0.62-0.73 and 0.59-0.70 for the glasses of the Ag2S–GeS2–As(Sb)2S3 systems, respectively, which indicates the high capacity of the samples to glass formation. Optical absorption spectra were measured at 297 K. The band gap energy Eg of the glasses of the Ag2S–GeS2–As(Sb)2S3 systems was estimated from the data on the spectral distribution of the absorption coefficient in the region of the absorption edge. It was determined that the absorption edge shifts to longer wavelengths with the increase of the GeS2 content in glasses, while the energy position of the absorption edge increases. Ade crease in the band gap energy is observed for all glass samples when a modifier is introduced into the glass-forming matrix. The characteristic energy of the degree of tailing of the absorption edge is in the range from 0.066 to 0.079 eV for all studied glass samples.
 Keywords: сhalcogenide glasses; quasi-ternary systems; glass-formation; characteristic temperatures; band gap energy.

Prediction of reduced glass transition temperature of metallic alloys based on a neural network

The reduced glass transition temperature Trg is an important glass forming ability parameter. Trg describes the glass formation in materials and the behaviour of materials at the transition between solid and liquid states and is an important parameter for materials analysis, development, and production process. This article describes the process and results of research on the development of a system for prediction of the reduced glass transition temperature Trg of metallic alloys based on recurrent neural network algorithms. The developed system can predict the reduced glass transition temperature Trg of metallic alloys based on the analysis of its chemical formula with high accuracy. The accuracy was evaluated using the 3 metrics: MSE, RMSE, MAE. Obtained values are: MSE value is 0.000678, RMSE value is 0.0260, MAE value is 0.01835.

Phase constitution and glass formation of U-Pd-Ni-Si alloys

In order to explore U-based alloys having high glass forming ability (GFA), a series of U-Pd-Ni-Si alloys with 60% U were designed on the basis of the eutectic features of U-Ni and U-Pd base systems together with the Si addition. Their ingots and ribbons were prepared by arc-melting and melt-spinning methods and further examined to reveal the phase constitution and amorphization behavior mainly by X-ray diffraction and differential scanning calorimetry. The results show that these alloys can form U6Ni type (NU) and/or α-U type (AU) phases under a quasi-equilibrium or equilibrium condition and amorphous phase, completely for most of them, under a non-equilibrium condition. A possibly Pd-based glassy phase seemed to unexpectedly arise in two Pd-rich alloy ingots, which would be the first observation of glass formation in U-based alloys solidified at low cooling rates. Within all the U-Pd-Ni-Si alloys, the ones with a big Ni/Pd ratio, thus tending to get NU phase, can achieve substantially higher GFA than the others with small Ni/Pd and a tendency to AU phase. Especially, U60Pd7.5Ni25Si7.5 and U60Pd5Ni25Si10 displayed firstly the reduced glass transition temperature Tg/TL of > 0.6 and a wide supercooled liquid region of ~100 K, exhibiting a GFA level superior to the whole reported U-based metallic glasses (MGs) and comparable to some traditional bulk MGs. All the yields reflect that Ni plays stronger roles in both compounding with U and the glass formation than Pd and Si in these alloys, and also offer guidance for creating novel U-based metallic materials including better MGs.

Correlations between Thermal Parameters and Glass Forming Abilities of Bulk Metallic Glasses Unveiled by Datamining

Datamining informatics techniques such as principal component analysis (PCA) and partial least squares (PLS) were applied to identify the composition characteristics of bulk metallic glasses with high glass forming abilities. It was pointed out that the reduced glass transition temperature T g /T l was comparatively the best indicator but no single indicator can reflect all the glass forming abilities of different alloy systems.

Designing bulk metallic glasses materials with higher reduced glass transition temperature via machine learning

Bulk metallic glasses (BMGs) are considered as one of the most promising candidates in the field of alloy materials due to their outstandingly high yield strengths and large elastic limits at ambient conditions compared to their crystalline counterparts. The formation of BMGs is determined by reduced glass transition temperature (Trg) that represents the glass forming ability (GFA). Experimental search for BMGs with higher Trg is a challenging task due to the vast chemical space and lack of predictive guidelines. Here, we demonstrate a machine learning approach to guide experimental synthesis in search of BMGs with higher Trg. The relationships between the Trg and chemical compositions of BMGs were investigated by using three different machine learning algorithms including support vector regression (SVR), back propagation artificial neural network (BPANN) and gradient boosting regression (GBR). The best predictions from SVR, BPANN, and GBR models were recommended for experimental tests. Based on the leave-one-out cross-validation (LOOCV), the correlation coefficient (R) and root mean squared error (RMSE) between predicted and experimental Trg were 0.894 and 0.0116, respectively. Furthermore, virtual screening based on machine learning results was adopted to design BMGs with higher Trg. The average relative error of Trg from newly synthesized BMGs is 1.00%, which is satisfactory compared to that of the known experimental samples (3.91%). Among the newly synthesized BMGs, Mg0.65Ag0.19Cu0.06Gd0.1 owns the highest Trg of 0.6658, exceeding the highest Trg (0.6576) in the reported experiments before.

Effects of drying methods on physical properties and morphology of trehalose/mannitol mixtures

Solid-state properties of dried protein formulations are important for stability and functionality of the product. This study investigates how different drying technologies (freeze-drying with and without annealing, spray drying and spray-freeze drying) affect the structure and solid-state properties of a set of matrix formulations composed of trehalose (glass former) and mannitol (scaffolding agent) in five ratios. The dried materials were characterized using differential scanning calorimetry, thermogravimetric analysis, x-ray diffraction and scanning electron microscopy. The morphology of the dried matrix is determined by the drying technology and the composition. In all mixtures, mannitol partially dissolved in the amorphous trehalose, resulting in reduced glass transition temperature. At least 50% mannitol is required to achieve a scaffolding effect through crystallized mannitol. At 25% mannitol poor structural stability is obtained regardless of drying technology. Despite the vast differences in drying kinetics, all drying technologies resulted in similar amorphous content in the dried material.

Environmental impact investigation on the interlaminar properties of carbon fibre composites modified with graphene nanoparticles

Graphene nanoparticles have been widely studied for their all-round promising positive effects. In this study, the effect of adding functionalised 2% NH2-graphene nanoparticles to carbon fibre/epoxy composite was assessed, before and after hygrothermal and ultraviolet exposure. The interlaminar shear strength and glass transition temperature of the filled and unfilled were experimentally determined, after being immersed in water at 25 °C, 40 °C and 70 °C until partially saturated. Other samples were exposed to ultraviolet for 700 and 1400 h. With graphene, samples showed up to 43.9% better water uptake resistance. The interlaminar shear strength decreased after immersion in water by an average of 5.8% with graphene, however, after ultraviolet exposure the ILSS loss commonly attributed to UV exposure was reduced by 12.1% with graphene. This improvement can be explained by the GNPs offering stability against free-radical ageing, slowing the rate of scissions and the eventual transformation to constituent monomers. Dynamical mechanical analysis on immersed samples showed that the graphene reduced glass transition temperature by only 1%. Filled samples exposed to UV for 1400 h suggested a reduction in glass transition temperature of 1 °C. Scanning electron microscopy revealed good dispersion of the GNPs in the epoxy matrix but with no strong bonding. • Graphene in carbon fibre had vast improvements to water uptake resistance of 43.9%. • Graphene improved strength resistance considerably after UV exposure by 12.1%. • Interlaminar shear strength decreased by 5.8% with graphene due to poor bonding.

Investigation on the Effect of Butyl Acrylate (nBA) to Improve the Toughness Properties of Methacrylate-Based Waterproofing Adhesive Material (MMA) for the Steel Bridge Deck

Waterproof adhesion materials (WAL) for steel bridge decks should have comprehensive strong bonding capabilities to steel substrates/pavement layers, water resistance, and persistence to harsh conditions. Methacrylate-based adhesive (MMA), as a typical WAL material for steel bridge decks, lacks sufficient flexibility and diverse compatibility. In this article, flexible, stabile at high temperature, and well-bonded poly (methyl methacrylate)/n-butyl acrylate copolymer [poly(MMA-r-nBA)] coatings were developed with toughening as a breakthrough point. The above properties are obtained by forming an interpenetrating network through interchain van der Waals forces. In addition to the flexibility provided by the long-chain structure of n-butyl acrylate, its unique molecular structure allows it to improve the high-temperature stability and lower the glass transition temperature of MMA. Due to the reduced glass transition temperature, it can also be matched to various pavement layers. Thus, the poly(MMA-r-nBA) composite polymer coatings can be applied to steel bridge decks that require long-term service in various conditions.

Composition dependence in glass-forming ability of Cu–Ag binary alloys

Alloys around eutectic points are thought to be good glass formers. However, the glass-forming ability (GFA) as a function of composition from pure metals to the eutectic alloy has not been quantified and the underlying microstructural and dynamical origins are unclear. In this work, the GFA of Cu–Ag alloys at various compositions was thoroughly investigated by using molecular dynamics simulations. According to the results, the critical cooling rate for glass formation Rc (K/s) varies with solute content x′ (at%), following Rc ≈ Aexp(kx′) where A = 4.61 × 1012 and k = -0.25 on the Cu side and A = 4.43 × 1012 and k = -0.19 on the Ag side. The Rc of the eutectic alloy is about 5 orders of magnitude lower than that of the pure metals. Structurally, the number of densely packed icosahedral-like clusters in Cu–Ag metallic glasses increases with increasing solute content, resulting in the most densely packed structure at the eutectic composition. The dynamical properties of Cu–Ag melts are basically independent on composition at high temperatures, but obviously change with composition at low temperature. Besides the largest reduced glass transition temperature, the highest five-fold symmetry (FFS) local structure and more importantly the retarded dynamics of liquid atoms below the liquidus temperature around the eutectic composition impart the eutectic alloy with the best glass-forming ability.