Critical Cooling Rate Vs. Reduced Glass Transition: Scaling Factors and Master Curves

1998 ◽  
Vol 554 ◽  
Author(s):  
N. Clavaguera ◽  
M. T. Clavaguera-Mora
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Cooling Rate ◽  
Glass Formation ◽  
Supercooled Liquid ◽  
High Viscosity ◽  
Master Curves ◽  
Critical Cooling Rate ◽  
Equilibrium Solidification

AbstractThe aim of the present paper is to analyse the glass formation and stability of bulk metallic glasses. Attention is focused to metallic alloys as systems which may develop a large glassforming ability. Glass formation when quenching from the liquid state is discussed in terms of the thermodynamics and kinetics of the stable/metastable competing phases. Thermodynamics is required to relate glass transition temperature, Tg, to the energetics of the supercooled liquid. Kinetic destabilisation of equilibrium solidification and, consequently, glass forming ability are favoured by the high viscosity values achieved under continuous cooling. The relative thermal stability of the supercooled liquid depends on the thermodynamic driving force and interfacial energy between each competing nucleating phase and the molten alloy. It is shown that the quantities representative of the process, once scaled, have a temperature dependence that is mostly fixed by the reduced glass transition temperature, Tgr= Tg/Tm, Tm being the melting temperature. Based on the classical models of nucleation and crystal growth, the reduced critical cooling rate is shown to follow master curves when plotted against Tgr. Experimental trends for specific systems are compared to predicted values from these master curves.

scholarly journals Effects of Annealing on Enthalpy Recovery and Nanomechanical Behaviors of a La-Based Bulk Metallic Glass

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 579
Author(s):  
Ting Shi ◽  
Lanping Huang ◽  
Song Li
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Metallic Glass ◽  
Bulk Metallic Glass ◽  
Structural Relaxation ◽  
Supercooled Liquid ◽  
Supercooled Liquid Region ◽  
Liquid Region ◽  
Nanoindentation Measurement

Structural relaxation and nanomechanical behaviors of La65Al14Ni5Co5Cu9.2Ag1.8 bulk metallic glass (BMG) with a low glass transition temperature during annealing have been investigated by calorimetry and nanoindentation measurement. The enthalpy release of this metallic glass is deduced by annealing near glass transition. When annealed below glass transition temperature for 5 min, the recovered enthalpy increases with annealing temperature and reaches the maximum value at 403 K. After annealed in supercooled liquid region, the recovered enthalpy obviously decreases. For a given annealing at 393 K, the relaxation behaviors of La-based BMG can be well described by the Kohlrausch-Williams-Watts (KWW) function. The hardness, Young’s modulus, and serrated flow are sensitive to structural relaxation of this metallic glass, which can be well explained by the theory of solid-like region and liquid-like region. The decrease of ductility and the enhancement of homogeneity can be ascribed to the transformation from liquid-like region into solid-like region and the reduction of the shear transition zone (STZ).

Dependence of the glass transition temperature on heating and cooling rate

1974 ◽  
Vol 78 (26) ◽  
pp. 2673-2677 ◽  
Author(s):  
Cornelius T. Moynihan ◽  
Allan J. Easteal ◽  
James Wilder ◽  
Joseph Tucker
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Cooling Rate ◽  
Heating And Cooling

Design rules for glass formation from model molecules designed by a neural-network-biased genetic algorithm

Soft Matter ◽  
2019 ◽  
Vol 15 (39) ◽  
pp. 7795-7808 ◽  
Author(s):  
Venkatesh Meenakshisundaram ◽  
Jui-Hsiang Hung ◽  
David S. Simmons
Keyword(s):  
Neural Network ◽  
Genetic Algorithm ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Glass Formation ◽  
Molecular Geometry ◽  
Design Model ◽  
Design Rules ◽  
Model Glass

A neural-network-biased genetic algorithm is employed to design model glass formers exhibiting extremes of fragility of glass formation, elucidating connections between molecular geometry, thermodynamics, fragility, and glass-transition temperature.

Strength of Sulfur-Linked Elastomers

1996 ◽  
Vol 69 (4) ◽  
pp. 577-590 ◽  
Author(s):  
H. Chun ◽  
A. N. Gent
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Crack Propagation ◽  
Test Temperature ◽  
Effective Rate ◽  
Master Curves ◽  
Universal Form ◽  
Wlf Equation ◽  
Test Conditions

Abstract Fracture energies have been determined for tearing through a sheet of a polysulfide elastomer, and for peeling apart two sheets bonded together with sulfur interlinks. Measurements were made over wide ranges of rate of crack propagation and test temperature. By shifting curves at various temperatures along the rate axis, using shift factors aT calculated from the “universal” form of the WLF equation, master curves were obtained for tear and peel energy vs. rate of tear or peel at the glass transition temperature Tg about −55°C. These master curves of strength vs. effective rate of crack propagation at Tg were closely similar to those obtained previously for several hydrocarbon elastomers: BR, SBR and EPR; interlinked with C-C bonds. Thus, under comparable test conditions the strength of the present polysulfide elastomer with sulfur crosslinks is similar to that for hydrocarbon elastomers with C-C crosslinks. The question then arises: Why are sulfur-vulcanized elastomers stronger in common experience than peroxide-cured ones? Possible reasons are discussed.

scholarly journals Oбобщенный кинетический критерий перехода жидкость--стекло

2020 ◽  
Vol 62 (10) ◽  
pp. 1706
Author(s):  
Д.С. Сандитов ◽  
В.В. Мантатов ◽  
С.Ш. Сангадиев
Keyword(s):  
Relaxation Time ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Cooling Rate ◽  
Glassy State ◽  
Fluctuation Volume ◽  
Dimensionless Constant ◽  
Transition Criterion

Using the model of delocalized atoms, a substantiation and generalization of the Schmelzer glass transition criterion is proposed. In contrast to the Bartenev and Volkenstein - Ptitsyn approaches, in the generalized kinetic glass transition criterion, along with the relaxation time and the cooling rate of the melt, the glass transition temperature and an almost universal dimensionless constant appear, which is determined by the fraction of the fluctuation volume frozen at the glass transition temperature. The idea is developed that the liquid goes into a glassy state when its cooling rate q reaches a certain fraction of C_g of the characteristic cooling rate q_g=(T_g/taug), which is closely related to the relaxation time of the structure tau_g at the glass transition temperature T_g.

scholarly journals Fractographic analysis of lithium silicate crown failures during sintering

2019 ◽  
Vol 7 ◽  
pp. 2050313X1983896
Author(s):  
Ulrich Lohbauer ◽  
Michael Wendler ◽  
Doreen Rapp ◽  
Renan Belli
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Cooling Rate ◽  
Computer Aided Design ◽  
Thermal Stresses ◽  
Point Contact ◽  
Lithium Silicate ◽  
Contact Points ◽  
Computer Aided

The two-step production process of glass-ceramic dental restorations involves a computer-aided design/computer-aided machining step followed by a crystallization firing for the final material properties to be achieved. Certain firing parameters are believed to trigger spontaneous fracture of crowns during the cooling process. In this study, cooling fractures have been reproducibly observed and investigated using fractography combined with material (glass transition temperature) and process (cooling rate) characterization. Stress distribution was visualized using birefringence measurements. Fractographic observations revealed fracture starting at the intaglio side of the crowns specifically at contact points with the support firing pins. Further analysis showed that a fast cooling rate was applied during the glass transition region. Thermal stresses were concentrated around the firing pin supports and released the fracture. To prevent such fractures, a slow cooling protocol below the glass transition temperature is our recommendation to dental technicians. Furthermore, the use of planar firing pad or paste supports is advised over the use of point contact supports.

Hot pressing and characterizations of mechanically alloyed Zr52Al6Ni8Cu14W20 glassy powders.

2006 ◽  
Vol 21 (4) ◽  
pp. 976-987 ◽  
Author(s):  
M. Sherif El-Eskandarany ◽  
A. Inoue
Keyword(s):  
Solid Solution ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Supercooled Liquid ◽  
Supercooled Liquid Region ◽  
Solution Phase ◽  
Solid Solution Phase ◽  
Liquid Region ◽  
Gradual Change

Low-energy ball milling technique was successfully used to synthesis new glassy Zr52Al6Ni8Cu14W20 multicomponent alloy powders using mechanical alloying method. During the intermediate stage of milling the atoms of Zr, Al, Ni, and Cu migrated and diffused into the W lattice to form a body-centered cubic solid solution phase. As the milling time increases, the obtained metastable powders are subsequently subjected to continuous defects and lattice imperfections that lead to a gradual change in the free energy so that solid solution phase transformed to another metastable phase (glassy). The glassy powders that were obtained after 720 ks milling are fully amorphous and have spherical-like morphology with an average particle size of 0.60 μm in diameter. The synthetic glassy Zr52Al6Ni8Cu14W20 alloy powder, which exhibits a glass transition temperature of 811 K, crystallizes at a high temperature (884 K) through a single sharp exothermic peak with an enthalpy change of crystallization of −5.48 kJ/mol. Whereas the supercooled liquid region before crystallization of the obtained glassy powders is 73 K, the reduced glass transition temperature (ratio between Tg and liquidus temperatures) was found to be 0.46. The fabricated glassy powders were consequently hot-pressed into bulk samples in an argon gas atmosphere at several temperatures with a pressure of 936 MPa. The samples that were consolidated within the temperature of the supercooled liquid region are fully dense, with relative density above ∼99.82%, and maintain their original homogeneous glassy structure. They have high Vickers microhardness values in the range between 8.46 and 8.62 GPa. They also show very high fracture strength (2.13 GPa) with an extraordinary high Young's modulus of 138 GPa. Neither yielding stress, nor plastic strain could be detected for this glassy alloy, the elastic strain of which is 1.47%.

scholarly journals 26. Invariance of the glass transition temperature of plant vitrification solutions with cooling rate

Cryobiology ◽  
2012 ◽  
Vol 65 (3) ◽  
pp. 347 ◽  
Author(s):  
Aline Schneider Teixeira ◽  
Miloš Faltus ◽  
Jiřı´ Zámečnı´k ◽  
Renata Kotková ◽  
Maria Elena González-Benito ◽  
...  
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Cooling Rate
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