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C T Liu - One of the best experts on this subject based on the ideXlab platform.
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effect of minor alloying additions on Glass Formation in bulk metallic Glasses
Intermetallics, 2005Co-Authors: C T LiuAbstract:Abstract This paper provides a comprehensive review of recent work on the effect of minor alloying additions on Glass Formation in bulk metallic Glasses. Recently, minor alloying addition or microalloying technology has shown to have dramatic effects on the Glass Formation and thermal stability of many bulk metallic Glasses. This technology basically involves adding small amounts of alloying additions (usually, less 2 at%) to existing bulk metallic Glasses for the purpose of further improving their Glass forming ability. Experimental evidences indicate that alloying additions of small atoms with atomic radius 0.16 nm (such as Y and Sc) are most effective in enhancing Glass forming ability. The beneficial effects of these elements are discussed in terms of physical metallurgy principles.
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a new approach to understanding and measuring Glass Formation in bulk amorphous materials
Intermetallics, 2004Co-Authors: C T LiuAbstract:Abstract This paper summarizes our recent work on the understanding of Glass Formation from considering both liquid phase stability and crystallization resistance from a physical metallurgical point of view. A comprehensive expression to predict Glass-forming ability (GFA) for various Glass-forming systems, γ=Tx/(Tg+Tl), was derived, where Tx is the crystallization temperature, Tg the Glass transition temperature and Tl the liquidus temperature. Our physical-metallurgy approach is supported strongly by experimental data reported for various bulk amorphous materials. Also, some misconception commonly used for assessing the GFA in the literature will be clarified.
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role of minor alloying additions in Formation of bulk metallic Glasses a review
Journal of Materials Science, 2004Co-Authors: C T LiuAbstract:Minor alloying addition or microalloying technology has already shown dramatic effects on Glass Formation and thermal stability of bulk metallic Glasses (BMGs). This paper intends to provide a comprehensive review of recent developments of this technology in the field of BMGs. The beneficial effects of minor alloying additions on the Glass Formation and the thermal stability of BMGs will be summarized and analyzed. In addition, principles and guidelines for future application of this technology will also be proposed.
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bulk Glass Formation in an fe based fe y zr m m cr co al mo b system
Journal of Materials Research, 2004Co-Authors: C T Liu, W D Porter, C A Carmichael, Seetharama C DeeviAbstract:Several new bulk metallic Glasses based on Fe–Y–Zr–(Co, Cr, Al)–Mo–B, which have a Glass-forming ability superior to the best composition Fe61Zr10Co7Mo5W2B15 reported recently, have been successfully developed. The as-cast bulk amorphous alloys showed a distinctly high thermal stability with Glass-transition temperatures above 900 K, supercooled liquid regions above 60 K, and high strength with Vickers hardness values larger than HV 1200. The suppression of the growth of primary phases in the molten liquids and the resultant low liquidus temperatures were found to be responsible for the superior Glass-forming ability in these new alloys. It was found that the addition of 2% Y not only facilitated bulk Glass Formation, but the neutralizing effect of Y with oxygen in the molten liquids also improved the manufacturability of these amorphous alloys.
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role of yttrium in Glass Formation of fe based bulk metallic Glasses
Applied Physics Letters, 2003Co-Authors: C T Liu, W D PorterAbstract:In this study, we discovered that a small addition of Y is very effective in improving Glass-forming ability of Fe-based alloys. As-cast bulk amorphous alloys containing 2 at. % Y showed large thermal stability, with Glass transition temperatures above 900 K and supercooled liquid regions above 55 K, and high strength, with Vickers hardnesses larger than HV 1200. The beneficial effect of Y on Glass Formation is twofold: (1) Y adjusted the compositions closer to the eutectic and thus lowered their liquidus temperatures, and (2) Y improved the manufacturability of these alloys by scavenging the oxygen impurity from it via the Formation of innocuous yttrium oxides.
Jack F Douglas - One of the best experts on this subject based on the ideXlab platform.
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polymer Glass Formation role of activation free energy configurational entropy and collective motion
arXiv: Soft Condensed Matter, 2021Co-Authors: Jack F Douglas, Zhaoyan SunAbstract:We provide a perspective on polymer Glass Formation, with an emphasis on models in which the fluid entropy and collective particle motion dominate the theoretical description and data analysis. We first discuss the dynamics of liquids in the high temperature Arrhenius regime, where transition state theory is formally applicable. We then summarize the evolution of the entropy theory from a qualitative framework for organizing and interpreting temperature-dependent viscosity data by Kauzmann to the formulation of a hypothetical `ideal thermodynamic Glass transition' by Gibbs and DiMarzio, followed by seminal measurements linking entropy and relaxation by Bestul and Chang and the Adam-Gibbs (AG) model of Glass Formation rationalizing the observations of Bestul and Chang. These developments laid the groundwork for the generalized entropy theory (GET), which merges an improved lattice model of polymer thermodynamics accounting for molecular structural details and enabling the analytic calculation of the configurational entropy with the AG model, giving rise to a highly predictive model of the segmental structural relaxation time of polymeric Glass-forming liquids. The development of the GET has occurred in parallel with the string model of Glass Formation in which concrete realizations of the cooperatively rearranging regions are identified and quantified for a wide range of polymeric and other Glass-forming materials. The string model has shown that many of the assumptions of AG are well supported by simulations, while others are certainly not, giving rise to an entropy theory of Glass Formation that is largely in accord with the GET. As the GET and string models continue to be refined, these models progressively grow into a more unified framework, and this Perspective reviews the present status of development of this promising approach to the dynamics of polymeric Glass-forming liquids.
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polymer Glass Formation role of activation free energy configurational entropy and collective motion
Macromolecules, 2021Co-Authors: Jack F Douglas, Zhaoyan SunAbstract:We provide a perspective on polymer Glass Formation, with an emphasis on models in which the fluid entropy and collective particle motion dominate the theoretical description and data analysis. The...
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understanding activation volume in Glass forming polymer melts via generalized entropy theory
Macromolecules, 2020Co-Authors: Jack F Douglas, Wenjie XiaAbstract:The generalized entropy theory (GET) of Glass Formation provides an analytic framework for the structural relaxation time and thermodynamic properties of Glass-forming polymers in terms of molecula...
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dynamic heterogeneity and collective motion in star polymer melts
Journal of Chemical Physics, 2020Co-Authors: Jinpeng Fan, Jack F Douglas, Hamed Emamy, Alexandros Chremos, Francis W StarrAbstract:While Glass Formation of linear chain polymer melts has widely been explored, comparatively little is known about Glass Formation in star polymer melts. We study the segmental dynamics of star polymer melts via molecular dynamics simulations and examine the cooperative nature of segmental motion in star melts. In particular, we quantify how the molecular architecture of star polymers, i.e., the number of arms and the length of those arms, affects the Glass transition temperature Tg, the non-Gaussian nature of molecular displacements, the collective string-like motion of monomers, and the role of chain connectivity in the cooperative motion. Although varying the number of arms f and the molecular mass Ma of the star arms can significantly influence the average star molecular shape, all our relaxation data can be quantitatively described in a unified way by the string model of Glass Formation, an activated transport model that derives from the Adam–Gibbs model, where the degree of cooperative motion is identified with the average length L of string-like particle exchange motions observed in our simulations. Previous work has shown the consistency of the string model with simulations of linear polymers at constant volume and constant pressure, as well as for thin supported polymer films and nanocomposites with variable polymer–surface interactions, where there are likewise large mobility gradients as in the star polymer melts studied in the present paper.
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Generalized entropy theory of Glass-Formation in fully flexible polymer melts
Journal of Chemical Physics, 2016Co-Authors: Wensheng Xu, Jack F Douglas, Karl F FreedAbstract:The generalized entropy theory (GET) offers many insights into how molecular parameters influence polymer Glass-Formation. Given the fact that chain rigidity often plays a critical role in understanding the Glass-Formation of polymer materials, the GET was originally developed based on models of semiflexible chains. Consequently, all previous calculations within the GET considered polymers with some degree of chain rigidity. Motivated by unexpected results from computer simulations of fully flexible polymer melts concerning the dependence of thermodynamic and dynamic properties on the cohesive interaction strength (ϵ), the present paper employs the GET to explore the influence of ϵ on Glass-Formation in models of polymer melts with a vanishing bending rigidity, i.e., fully flexible polymer melts. In accord with simulations, the GET for fully flexible polymer melts predicts that basic dimensionless thermodynamic properties (such as the reduced thermal expansion coefficient and isothermal compressibility) are universal functions of the temperature scaled by ϵ in the regime of low pressures. Similar scaling behavior is also found for the configurational entropy density in the GET for fully flexible polymer melts. Moreover, we find that the characteristic temperatures of Glass-Formation increase linearly with ϵ and that the fragility is independent of ϵ in fully flexible polymer melts, predictions that are again consistent with simulations of Glass-forming polymer melts composed of fully flexible chains. Beyond an explanation of these general trends observed in simulations, the GET for fully flexible polymer melts predicts the presence of a positive residual configurational entropy at low temperatures, indicating a return to Arrhenius relaxation in the low temperature Glassy state.
Karl F Freed - One of the best experts on this subject based on the ideXlab platform.
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Generalized entropy theory of Glass-Formation in fully flexible polymer melts
Journal of Chemical Physics, 2016Co-Authors: Wensheng Xu, Jack F Douglas, Karl F FreedAbstract:The generalized entropy theory (GET) offers many insights into how molecular parameters influence polymer Glass-Formation. Given the fact that chain rigidity often plays a critical role in understanding the Glass-Formation of polymer materials, the GET was originally developed based on models of semiflexible chains. Consequently, all previous calculations within the GET considered polymers with some degree of chain rigidity. Motivated by unexpected results from computer simulations of fully flexible polymer melts concerning the dependence of thermodynamic and dynamic properties on the cohesive interaction strength (ϵ), the present paper employs the GET to explore the influence of ϵ on Glass-Formation in models of polymer melts with a vanishing bending rigidity, i.e., fully flexible polymer melts. In accord with simulations, the GET for fully flexible polymer melts predicts that basic dimensionless thermodynamic properties (such as the reduced thermal expansion coefficient and isothermal compressibility) are universal functions of the temperature scaled by ϵ in the regime of low pressures. Similar scaling behavior is also found for the configurational entropy density in the GET for fully flexible polymer melts. Moreover, we find that the characteristic temperatures of Glass-Formation increase linearly with ϵ and that the fragility is independent of ϵ in fully flexible polymer melts, predictions that are again consistent with simulations of Glass-forming polymer melts composed of fully flexible chains. Beyond an explanation of these general trends observed in simulations, the GET for fully flexible polymer melts predicts the presence of a positive residual configurational entropy at low temperatures, indicating a return to Arrhenius relaxation in the low temperature Glassy state.
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generalized entropy theory of Glass Formation in fully flexible polymer melts
arXiv: Soft Condensed Matter, 2016Co-Authors: Jack F Douglas, Karl F FreedAbstract:The generalized entropy theory (GET) offers many insights into how molecular parameters influence polymer Glass-Formation. Given the fact that chain rigidity often plays a critical role in understanding the Glass-Formation of polymer materials, the GET was originally developed based on models of semiflexible chains. Consequently, all previous calculations within the GET considered polymers with some degree of chain rigidity. Motivated by unexpected results from computer simulations of fully flexible polymer melts concerning the dependence of thermodynamic and dynamic properties on the cohesive interaction strength ($\epsilon$), the present paper employs the GET to explore the influence of $\epsilon$ on Glass-Formation in models of polymer melts with a vanishing bending rigidity, i.e., fully flexible polymer melts. In accord with simulations, the GET for fully flexible polymer melts predicts that basic dimensionless thermodynamic properties (such as the thermal expansion coefficient and isothermal compressibility) are universal functions of the temperature scaled by $\epsilon$ in the regime of low pressures. Similar scaling behavior is also found for the configurational entropy density in the GET for fully flexible polymer melts. Moreover, we find that the characteristic temperatures of Glass-Formation increase linearly with $\epsilon$ and that the fragility is independent of $\epsilon$ in fully flexible polymer melts, predictions that are again consistent with simulations of Glass-forming polymer melts composed of fully flexible chains. Beyond an explanation of these general trends observed in simulations, the GET for fully flexible polymer melts predicts the presence of a positive residual configurational entropy at low temperatures, indicating a return to Arrhenius relaxation in the low temperature Glassy state.
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self assembly and Glass Formation in a lattice model of telechelic polymer melts influence of stiffness of the sticky bonds
arXiv: Soft Condensed Matter, 2016Co-Authors: Wensheng Xu, Karl F FreedAbstract:The lattice cluster theory (LCT) for strongly interacting, self-assembling telechelic polymers provides a theoretical tool that enables establishing the connections between important microscopic molecular details of self-assembling polymers and their bulk thermodynamics. The original LCT for self-assembly of telechelic polymers considers a model of fully flexible linear chains [J. Dudowicz and K. F. Freed, J. Chem. Phys. \textbf{136}, 064902 (2012)], while our recent work introduces a significant improvement to the LCT by including a description of chain semiflexibility for the bonds within each individual telecheic chain [W.-S. Xu and K. F. Freed, J. Chem. Phys. \textbf{143}, 024901 (2015)], but the physically associative (or called "sticky") bonds between the ends of the telechelics are left as fully flexible. Motivated by the ubiquitous presence of steric constraints on the association of real telechelic polymers that impart an additional degree of bond stiffness (or rigidity), the present paper further extends the LCT to permit the sticky bonds to be semiflexible but to have a stiffness differing from that within each telechelic chain. An analytical expression for the Helmholtz free energy is provided for this model of linear telechelic polymer melts, and illustrative calculations demonstrate the significant influence of the stiffness of the sticky bonds on the self-assembly and thermodynamics of telechelic polymers. A brief discussion is also provided for the impact of self-assembly on Glass-Formation by combining the LCT description for this extended model of telechelic polymers with the Adam-Gibbs relation between the structural relaxation time and the configurational entropy.
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communication the simplified generalized entropy theory of Glass Formation in polymer melts
Journal of Chemical Physics, 2015Co-Authors: Karl F FreedAbstract:While a wide range of non-trivial predictions of the generalized entropy theory (GET) of Glass-Formation in polymer melts agree with a large number of observed universal and non-universal properties of these Glass-formers and even for the dependence of these properties on monomer molecular structure, the huge mathematical complexity of the theory precludes its extension to describe, for instance, the perplexing, complex behavior observed for technologically important polymer films with thickness below ∼100 nm and for which a fundamental molecular theory is lacking for the structural relaxation. The present communication describes a hugely simplified version of the theory, called the simplified generalized entropy theory (SGET) that provides one component necessary for devising a theory for the structural relaxation of thin polymer films and thereby supplements the first required ingredient, the recently developed Flory-Huggins level theory for the thermodynamic properties of thin polymer films, before the concluding third step of combining all the components into the SGET for thin polymer films. Comparisons between the predictions of the SGET and the full GET for the four characteristic temperatures of Glass-Formation provide good agreement for a highly non-trivial model system of polymer melts with chains of the structure of poly(n-α olefins) systems where the GET has produced good agreement with experiment. The comparisons consider values of the relative backbone and side group stiffnesses such that the Glass transition temperature decreases as the amount of excess free volume diminishes, contrary to general expectations but in accord with observations for poly(n-alkyl methacrylates). Moreover, the SGET is sufficiently concise to enable its discussion in a standard course on statistical mechanics or polymer physics.
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advances in the generalized entropy theory of Glass Formation in polymer melts
Journal of Chemical Physics, 2014Co-Authors: Jacek Dudowicz, Jack F Douglas, Karl F FreedAbstract:The generalized entropy theory (GET) of polymeric Glass-forming liquids is reformulated into a computationally simpler and more natural formalism than the original version of this theory. The new theoretical framework greatly facilitates establishing essential trends in the dependence of the segmental relaxation time τ, fragility, characteristic temperatures of Glass-Formation, etc., on the combined influences of monomer molecular structure, chain rigidity, and cohesive interaction strength. Special attention is placed on the estimating the parameters of the phenomenological Vogel-Fulcher-Tammann relations for describing segmental relaxation in diverse liquids in the low temperature range of Glass-Formation, Tg > T > Tc (or Tg < T < Tg + 100 K), where Tg and Tc are, respectively, the Glass transition temperature and the crossover temperature separating the high and low temperature regimes of Glass-Formation. Finally, we discuss how the molecular energetic interaction parameters of the GET can be estimated...
Akihisa Inoue - One of the best experts on this subject based on the ideXlab platform.
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bulk metallic Glass Formation by melting liquid joining method
Materials Transactions, 2008Co-Authors: Xinmin Wang, Akihisa InoueAbstract:There were many techniques of joining two or three materials. A new metallic liquid jointing technique which enables the joint of Zr 55 Cu 30 Ni 5 Al 10 bulk Glassy alloy without any crystallization is very useful to produce a large bulk metallic Glass. Molten alloy streams with high velocity are generated by ejection of alloy liquid through two nozzles at different sites. The jointed region has nearly the same structure, thermal stability and mechanical properties as those for the original Glassy Zr 55 Cu 30 Ni 5 Al 10 alloy. The successful joint method can produce the large Glassy Zr 55 Cu 30 Ni 5 Al 10 rod of 600mm in length and 3 mm in diameter.
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a study of Glass Formation Formation of the supercooled liquid and devitrification behavior of ni based bulk Glass forming alloys
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2007Co-Authors: D V Louzguineluzgin, Takeyuki Shimada, Akihisa InoueAbstract:Abstract Glass-Formation and devitrification of the Glassy phase in the Ni–Nb–Zr–Ti and Ni–Nb–Zr–Ti–NM (NM, noble metals) system alloys exhibiting the supercooled liquid on heating were investigated. The crystallized structure and kinetics of devitrification of Ni–Nb–Zr–Ti–Pd Glassy alloy are studied in detail. The Formation of the Glassy single phase has been proven using high-resolution transmission electron microscopy (TEM). The addition of Zr and Pd increases the supercooled liquid region of the Ni 60 Nb 25 Ti 15 (numbers indicate at.%) alloy from 44 K to about 50 K. The cP2 TiNi phase was found to form during the first exothermic phase transFormation in all studied alloys. The addition of Zr to Ni–Nb–Ti alloy prevents Formation of oP8 Ni 3 Nb phase observed in the Ni 60 Nb 25 Ti 15 alloy and initiates Formation of the primary Ni 10 Zr 7 phase while the additions of both NM and Zr effectively refine cP2 TiNi particles size. Definite fractions of rhombohedral R and hR14 Ni 4 Ti 3 phases were also observed in NM-bearing alloys. Significantly lower growth rates of the devitrification products in the NM-bearing alloys compared to the Ni–Nb–Ti one may be the reason for the improvement of Glass-forming ability (GFA).
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effects of chromium on the Glass Formation and corrosion behavior of bulk Glassy fe cr mo c b alloys
Materials Transactions, 2002Co-Authors: Shujie Pang, Tao Zhang, K Asami, Akihisa InoueAbstract:Bulk Glassy Fe 60-x Cr x Mo 15 C 15 B 10 (x = 0, 7.5, 15, 22.5 and 30 at%) alloys with high thermal stability were synthesized and the effects of chromium on the Glass Formation and corrosion behavior were clarified. The maximum diameter for Glass Formation is 2-2.5 mm for the 7.5 and 15 at%Cr alloys and 1 mm for the other alloys. In the present Glassy alloy system, the temperature interval of the supercooled liquid region (ΔT x ) changed with chromium and was enlarged from around 70 K at x = 0, 22.5 and 30 at% to over 80 K at x = 7.5 and 15 at%. Both corrosion rate and anodic current density by potentiodynamic polarization in HCl solutions decreased with an increase of chromium content in the alloys. For the Cr-free alloy, molybdenum was significantly concentrated in the surface film after immersion in 1 N HCI solution. The bulk Glassy alloys containing chromium was immune to corrosion by the Formation of protective passive film enriched with chromium during immersion in the solution.
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supercooling investigation and critical cooling rate for Glass Formation in pd cu ni p alloy
Acta Materialia, 1999Co-Authors: Akihisa InoueAbstract:Abstract Based on the previous results of undercooling investigation, the critical cooling rate for Glass Formation ( R c ) and crystallization behavior of the Pd 40 Cu 30 Ni 10 P 20 alloy are determined and compared with theoretical calculation results using the classical nucleation theory (CNT). As nucleating homogeneously, the R c is evaluated to be 2.08×10 −5 K/s under continuous cooling, which is underestimated by four orders of magnitude against the experimental results. Actual crystallization of the alloy is dominated by a heterogeneous nucleation mechanism. Considering foreign substrate-induced nucleation, the wetting angle ( θ ) between crystalline embryo and undercooled melt is evaluated to be about 62.5°. Furthermore, other heterogeneous nucleation mechanisms beyond the CNT are discussed to fit the experimental results.
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effect of additional elements on Glass transition behavior and Glass Formation tendency of zr al cu ni alloys
Materials Transactions Jim, 1995Co-Authors: Akihisa Inoue, Tsutomu Shibata, Tao ZhangAbstract:The Glass transition temperature (T g ) and crystallization temperature (T x ) of the Zr 65 Al 10 Cu 15 Ni 10 base Glassy alloys containing additional M (M=Ti, Hf, V, Nb, Cr, Mo, Fe, Co, Pd or Ag) elements were examined as a function of M elements, with the aim of finding an effective element for the increase in ΔT x ( = T x - T g ) and of confirming the appropriateness of the previous empirical rules for the appearance of large ΔT x . As the additional amount of the M elements except Hf increases, T g increases gradually, whereas T x decreases significantly and leads to the decrease in ΔT x . No effective M element leading to the increase in ΔT x is found. The ineffectiveness is attributed to the partial generation of repulsive bonding nature of Cu-M (M=V, Nb, Cr, Mo, Fe, Co, Pd or Ag) and Zr-M (M=Ti of Hf) pairs which does not satisfy the empirical rules. The area ratio of the Glassy region in the arc-melted ingots with a maximum thickness of about 8 mm was found to increase from 67% for the Zr-Al-Cu-Ni alloy to about 90% for the Zr-based alloys containing 5%Ti, 2.5%Nb or 5%Pd, though ΔT x decreases significantly by the addition of these elements. The great effectiveness of the three elements on the Glass-Formation tendency in the arc-melted ingots is interpreted to originate from the suppression of the growth reaction of crystalline nulcei which pre-exist in the arc-melted alloy. Furthermore, the disagreement between the Glass-Formation tendency evaluated by ΔT x and the area ratio of the Glassy region is thought to result from the difference in the dominant factors which are the crystalline nucleation and growth reactions for the ΔT x of the melt-spun Glassy alloys and the growth reaction for the area ratio of the Glassy region in the arc-melted ingot. The finding of the additional elements leading to the increase in the Glass-Formation tendency of the arc-melted alloys, regardless of the magnitude of ΔT x , seems to be a very encouraging event for future development of bulk Glassy alloys.
J Xu - One of the best experts on this subject based on the ideXlab platform.
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a new composition zone of bulk metallic Glass Formation in the cu zr ti ternary system and its correlation with the eutectic reaction
Journal of Non-crystalline Solids, 2008Co-Authors: Yat Li, J XuAbstract:A new composition region of bulk metallic Glass Formation, around Cu52Zr40Ti8, was discovered in the Cu– Zr–Ti ternary system, for which monolithic bulk metallic Glass rods of 4 mm in diameter can be fabricated using copper mold casting. The solidification of the Cu52Zr40Ti8 deeply-undercooled liquid mainly undergoes a univariant eutectic reaction, (L ? Cu10Zr7 + CuZr), even though this composition was predicted to be a ternary eutectic point (L ? Cu10Zr7 + CuZr + Cu2ZrTi) by CALPHAD calculations. With respect to the deep-eutectic reaction of (L ? Cu10Zr7 + CuZr) in the Cu–Zr binary alloys, alloying of Ti has a significant effect on further stabilizing the liquid, as indicated as a drop of the univariant eutectic groove, limiting the coupled growth of two crystalline phases, hence increasing the Glass-forming ability.
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doubling the critical size for bulk metallic Glass Formation in the mg cu y ternary system
Journal of Materials Research, 2005Co-Authors: Qiang Zheng, J Xu, Yat LiAbstract:Mg-Cu-Y alloys with optimal Glass forming ability have been found at off-eutectic compositions. The critical size for bulk metallic Glass Formation at the pinpointed compositions more than doubles that of the previously discovered eutectic Mg65Cu25Y10 alloy, leading to fully Glassy rods with near-centimeter diameters in the ternary system upon copper mold casting. The result is a striking demonstration of the strong composition dependence of the Glass forming ability, as well as of the need to scrutinize off-eutectic compositions. The implications of the discovery are discussed.
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Glass Formation in a ti zr hf cu ni ag al high order alloy system by mechanical alloying
Journal of Materials Research, 2003Co-Authors: L C Zhang, Z Q Shen, J XuAbstract:In this work, Glass Formation under high-energy ball milling was investigated for a (Ti 0.33 Zr 0.33 Hf 0.33 ) 50 (Ni 0.33 Cu 0.33 Ag 0.33 ) 40 Al 10 high-order alloy system with equiatomic substitution for early and late transition-metal contents. For comparison, an amorphous alloy ribbon with the same composition was prepared using the melt-spinning method as well. Structural features of the samples were characterized using x-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. Mechanical alloying resulted in a Glassy alloy similar to that obtained by melt spinning. However, the Glass Formation was incomplete, and a small amount of unreacted crystallites smaller than 30 nm in size still remained in the final ball-milled product. Like the melt-spun Glass, the ball-milled Glassy alloy also exhibited a distinct Glass transition and a wide supercooled liquid region of about 80 K. Crystallization of this high-order Glassy alloy proceeded through two main stages. After the primary nanocrystallization was completed, the remaining amorphous phase also behaved as a Glass, showing a detectable Glass transition and a large supercooled liquid region of about 100 K.
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Bulk metallic Glass Formation in the Mg-Cu-Zn-Y system
Scripta Materialia, 2002Co-Authors: Z Q Hu, J XuAbstract:The element Cu in the bulk Glass-forming alloy Mg65Cu25Y10 was substituted with the element Zn to form a Mg65Cu10Zn5Y10 alloy, which caused a significant improvement of the Glass-forming ability of Mg65Cu25Y10 alloy. For the Mg65Cu20Zn5Y10 alloy, fully Glassy rod with a 6-mm diameter can be obtained by copper mold casting. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
