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We probe the influence of branching on the configurational, packing, and density correlation function properties of polymer melts of linear and star polymers, with emphasis on molecular masses larger than the entanglement molecular mass of linear chains. In particular, we calculate the conformational properties of these polymers, such as the hydrodynamic radius R h , packing length p, pair correlation function g ( r ) , and polymer center of mass self-diffusion coefficient, D, with the use of coarse-grained molecular dynamics simulations. Our simulation results reproduce the phenomenology of simulated linear and branched polymers, and we attempt to understand our observations based on a combination of hydrodynamic and thermodynamic modeling. We introduce a model of “entanglement” phenomenon in high molecular mass polymers that assumes polymers can viewed in a coarse-grained sense as “soft” particles and, correspondingly, we model the emergence of heterogeneous dynamics in polymeric glass-forming liquids to occur in a fashion similar to glass-forming liquids in which the molecules have soft repulsive interactions. Based on this novel perspective of polymer melt dynamics, we propose a functional form for D that can describe our simulation results for both star and linear polymers, covering both the unentangled to entangled polymer melt regimes.

Excellent mechanical and physical properties like high thermal resistance, high hardness, and chemical stability have encouraged the use of ceramics in various applications such as automotive engines, electronic substrates for microwave devices, dielectric materials, etc. The hard and brittle nature of these ceramics makes them difficult to cut using conventional machining due to large cutting forces as well as severe tool wear involved for such hard-to-cut material. Thus, non-contact laser machining is suitable to cut the hard and brittle ceramics. A highly focused laser beam strikes the workpiece with a high energy such that the temperature of the workpiece exceeds its boiling temperature, resulting in vaporization and ablation. In this paper, an experimental investigation of the laser cutting of 7 mm thick ceramic panels, commonly used as glazed floor tiles, is carried out using a fiber laser. The present study involves a systematic experimental investigation with the aim of evaluating the influence of the input process parameters, namely laser power, frequency, scanning speed and gas pressure on kerf widths on the top and bottom surfaces, glass formation width on the bottom surface and taper angle. Based on the experimental results, regression equations are developed to estimate the responses as functions of the laser process parameters and gas pressure. Investigations reveal that kerf widths on the top and the bottom surfaces, glass formation width, and taper angle increases with laser power and decreases with increasing scanning speed at constant gas pressure and frequency. Moreover, glass formation width increases with increasing frequency at constant laser power and gas pressure, decreases with increasing frequency at constant scanning speed and gas pressure. The optimum process parameters are also found based on minimizing the taper angle at relatively low operating energy cost by minimizing the line energy, i.e., by minimizing laser power, P and maximizing scanning speed, V .

The microstructure, glass formation ability, and magnetic properties of Fe79Si9B6Nb5Cu1 alloy with different hydrogenation were studied. Results show that hydrogenation can improve the glass formation ability from 91.0(0.01) to 123.5(0.01) K, reduce the grain size, increase the saturation magnetization first, and then decrease, increase the coercivity.

We prepared Fe80Si8B6Nb5Cu amorphous-nanocrystalline strips with different phosphorus addition by the melt spinning method, and their nanocrystalline magnetic powder core was obtained after a series of processing. Then, the microstructure, micromorphology, thermal behavior, and magnetic properties were studied. The results show that the atomic radius difference (σ) affected the glass formation ability; thus, first, the grain size and coercivity decreased and then increased. The (Fe80Si8B6Nb5Cu)99P nanocrystalline core has the better comprehensive magnetic properties than those of Fe80Si8B6Nb5Cu; its μe (75.93) is 5% higher, and Pcm (370 W/kg) is 14% lower than those of Fe80Si8B6Nb5Cu (i.e., 72.98 and 431.2 W/kg, respectively).

The dynamics of a supercooled liquid near the glass transition is characterized by two-step relaxation, fastβand slowαrelaxations. Because of the apparently disordered nature of glassy structures, there have been long debates over whether the origin of drastic slowing-down of theαrelaxation accompanied by heterogeneous dynamics is thermodynamic or dynamic. Furthermore, it has been elusive whether there is any deep connection between fastβand slowαmodes. To settle these issues, here we introduce a set of new structural order parameters characterizing sterically favored structures with high local packing capability, and then access structure-dynamics correlation by a novel nonlocal approach. We find that the particle mobility is under control of the static order parameter field. The fastβprocess is controlled by the instantaneous order parameter field locally, resulting in short-time particle-scale dynamics. Then the mobility field progressively develops with timet, following the initial order parameter field from disorder to more ordered regions. As is well known, the heterogeneity in the mobility field (dynamic heterogeneity) is maximized with a characteristic lengthξ4, whentreaches the relaxation timeτα. We discover that this mobility pattern can be predicted solely by a spatial coarse graining of the initial order parameter field att=0over a lengthξwithout any dynamical information. Furthermore, we find a relationξ∼ξ4, indicating that the static lengthξgrows coherently with the dynamic oneξ4upon cooling. This further suggests an intrinsic link betweenταandξ: the growth of the static lengthξis the origin of dynamical slowing-down. These we confirm for the first time in binary glass formers both in two and three spatial dimensions. Thus, a static structure has two intrinsic characteristic lengths, particle size andξ, which control dynamics in local and nonlocal manners, resulting in the emergence of the two key relaxation modes, fastβand slowαprocesses, respectively. Because the two processes share a common structural origin, we can even predict a dynamic propensity pattern at long timescale from the fastβpattern. The presence of such intrinsic structure-dynamics correlation strongly indicates a thermodynamic nature of glass transition.

The influence of oxygen on the glass formation and the structure of oxyfluoride glasses has been considered using different glass systems containing fluorine and oxygen.

Since their discovery in 1960 1 , metallic glasses based on a wide range of elements have been developed 2 . However, the theoretical prediction of glass-forming compositions is challenging and the discovery of alloys with specific properties has so far largely been the result of trial and error 3 – 8 . Bulk metallic glasses can exhibit strength and elasticity surpassing those of conventional structural alloys 9 – 11 , but the mechanical properties of these glasses are critically dependent on the glass transition temperature. At temperatures approaching the glass transition, bulk metallic glasses undergo plastic flow, resulting in a substantial decrease in quasi-static strength. Bulk metallic glasses with glass transition temperatures greater than 1,000 kelvin have been developed, but the supercooled liquid region (between the glass transition and the crystallization temperature) is narrow, resulting in very little thermoplastic formability, which limits their practical applicability. Here we report the design of iridium/nickel/tantalum metallic glasses (and others also containing boron) with a glass transition temperature of up to 1,162 kelvin and a supercooled liquid region of 136 kelvin that is wider than that of most existing metallic glasses 12 . Our Ir–Ni–Ta–(B) glasses exhibit high strength at high temperatures compared to existing alloys: 3.7 gigapascals at 1,000 kelvin 9 , 13 . Their glass-forming ability is characterized by a critical casting thickness of three millimetres, suggesting that small-scale components for applications at high temperatures or in harsh environments can readily be obtained by thermoplastic forming 14 . To identify alloys of interest, we used a simplified combinatorial approach 6 – 8 harnessing a previously reported correlation between glass-forming ability and electrical resistivity 15 – 17 . This method is non-destructive, allowing subsequent testing of a range of physical properties on the same library of samples. The practicality of our design and discovery approach, exemplified by the identification of high-strength, high-temperature bulk metallic glasses, bodes well for enabling the discovery of other glassy alloys with exciting properties. Bulk metallic glasses made from alloys of iridium, nickel, tantalum and boron are developed by combinatorial methods, with higher strength at high temperature than those previously produced.

Successful computer studies of glass-forming materials need to overcome both the natural tendency to structural ordering and the dramatic increase of relaxation times at low temperatures. We present a comprehensive analysis of eleven glass-forming models to demonstrate that both challenges can be efficiently tackled using carefully designed models of size polydisperse supercooled liquids together with an efficient Monte Carlo algorithm where translational particle displacements are complemented by swaps of particle pairs. We study a broad range of size polydispersities, using both discrete and continuous mixtures, and we systematically investigate the role of particle softness, attractivity, and nonadditivity of the interactions. Each system is characterized by its robustness against structural ordering and by the efficiency of the swap Monte Carlo algorithm. We show that the combined optimization of the potential’s softness, polydispersity, and nonadditivity leads to novel computer models with excellent glass-forming ability. For such models, we achieve over 10 orders of magnitude gain in the equilibration time scale using the swap Monte Carlo algorithm, thus paving the way to computational studies of static and thermodynamic properties under experimental conditions. In addition, we provide microscopic insight into the performance of the swap algorithm, which should help optimize models and algorithms even further.

Despite the importance of glass forming ability as a major alloy characteristic, it is poorly understood and its quantification has been experimentally laborious and computationally challenging. Here, we uncover that the glass forming ability of an alloy is represented in its amorphous structure far away from equilibrium, which can be exposed by conventional X-ray diffraction. Specifically, we fabricated roughly 5,700 alloys from 12 alloy systems and characterized the full-width at half-maximum, Δ q , of the first diffraction peak in the X-ray diffraction pattern. A strong correlation between high glass forming ability and a large Δ q was found. This correlation indicates that a large dispersion of structural units comprising the amorphous structure is the universal indicator for high metallic glass formation. When paired with combinatorial synthesis, the correlation enhances throughput by up to 100 times compared to today’s state-of-the-art combinatorial methods and will facilitate the discovery of bulk metallic glasses. The glass forming ability of alloys is found to be strongly correlated with the full-width at half-maximum of the first diffraction peak in the X-ray diffraction pattern, which facilitates the discovery of bulk metallic glass compositions.

Glass formation is encountered in diverse materials. Experiments have revealed that the dynamic relaxation spectra of supercooled liquids generically become asymmetric near the glass transition temperature T g , where an extended power law emerges at high frequencies. The microscopic origin of this ‘wing’ remains unknown, and has so far been inaccessible to simulations. Here we develop a novel computational approach and study the equilibrium dynamics of model supercooled liquids near T g . We demonstrate the emergence of a power-law wing in the numerical spectra, which originates from relaxation at rare, localized regions over broadly distributed timescales. We rationalize the asymmetric shape of the relaxation spectra by constructing an empirical model associating heterogeneous activated dynamics with dynamic facilitation, which are the two minimal physical ingredients revealed by our simulations. Our work offers a glimpse into the molecular motion responsible for glass formation at relevant experimental conditions. The dynamic relaxation spectrum of a supercooled liquid is asymmetric near the glass transition. Overcoming the difficulty of accessing low temperatures and long timescales, simulations now attribute this feature to dynamic facilitation.