Compositions with easy bulk metallic glass formation have been identified in quinary systems with the Gibbs-energy change between the amorphous and solid solution phases as the thermodynamic parameter. The Gibbs-energy change has been calculated with the help of Miedema, Miracle, mismatch entropy, and configurational entropy models. The best glass forming composition has been identified by drawing iso-Gibbs-energy change contours by representing quinary systems as pseudo-ternary ones. Attempts have been made to correlate the Gibbs-energy change with different existing glass forming criteria and it is found that the present thermodynamic parameter has good correlation with the reduced glass transition temperature. Further, encouraging correlations have been obtained between the energy required for amorphization during mechanical alloying to the Gibbs-energy change between the amorphous and solid solutions. © 2006 Elsevier B.V. All rights reserved.

Srinivasa Rao Bakshi

Department of Metallurgical and Materials Engineering

Budaraju Srinivasa Murty

Forming

Gibbs free energy

glass transition

Mechanical Alloying

Temperature

Thermodynamics

Topology

Bulk metallic glass

GLASS FORMING

MULTICOMPONENT SYSTEMS

Metallic glass

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IIT Madras

Materials Science and Engineering A

Topological factors such as mismatch entropy and configurational entropy, along with thermodynamic entity such as enthalpy of chemical mixing, are found to control glass formation in metallic systems. Taking both these factors into consideration, a parameter called P HS was proposed to correlate glass forming ability successfully in the Cu-Zr-Ti system. The parameter P HS (=ΔH chem × ΔS σ /k B ) is a product of enthalpy of chemical mixing and mismatch entropy. Our study indicates that the more negative is the PHS value within the configurational entropy (ΔS config/R) range of 0.9 to 1.0, the higher is the stability of glassy phase resulting in a larger diameter of bulk metallic glass rods. Observed theoretical predictions are supported by experimental results in which the compositions with high negative P HS resulted in easy amorphous phase formation in comparison with less negative P HS compositions by mechanical alloying. This criterion was extended to Cu-Zr-Al and Cu-Zr-Ag systems as well, thus establishing a strong correlation between P HS and the glass forming ability of alloys. The role of size effect, probability of atomic arrangements, and heat of formation among constituent elements in obtaining a larger dimension bulk metallic glasses was addressed in this study. © 2013 The Minerals, Metals &amp; Materials Society and ASM International.

Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

Thermodynamic basis for glass formation in Cu-Zr rich ternary systems and their synthesis by mechanical alloying

CALPHAD approach has been used to predict the stable phases, their relative amounts and compositions in multicomponent equiatomic high entropy alloys. The results show a good match between the predictions and experimental results on the phase formation for two equiatomic high entropy alloys (CrCoCuNi and CrCuMnNi alloys) prepared by mechanical alloying, considering the kinetic constraints of the non-equilibrium processing route. © Indian Institute of Metals 2012.

Transactions of the Indian Institute of Metals

Phase formation in equiatomic high entropy alloys: CALPHAD approach and experimental studies

This paper attempts to optimize the bulk metallic glass forming compositions using enthalpy of chemical mixing (ΔHchem) as thermodynamic, mismatch entropy (ΔSσ/kB) as topological and configurational entropy (ΔSconfig/R) as statistical parameters. The product of ΔHchem and ΔS σ/kB which is termed as PHS in the ΔSconfig/R range of 0.9 to 1.0 can be correlated strongly to glass forming ability. PHS being an important parameter has been used to design the quaternary and quinary Bulk Metallic Glass compositions from ternary compositions. This has been demonstrated for two Zr rich quaternary systems in Zr-Ti-Cu-Ni and Zr-Cu-Ni-Al based bulk metallic glasses. By weighing approach of PHS of four Zr rich quaternary systems and one non-Zr rich systems a new Zr rich quinary bulk metallic glass in Zr-Ti-Cu-Ni-Al system is designed. Mechanical alloying is used to prepare the bulk amorphous powder at the compositions predicted by the model in order to validate the model. © (2010) Trans Tech Publications.

Materials Science Forum

Identification of bulk metallic forming compositions through thermodynamic and topological models

In the present study, an attempt has been made to develop milling maps/energy maps for the formation of amorphous phase in bulk glass forming alloys such as Zr65Al7.5Cu17.5Ni10, Ti50Cu23Ni20Sn7, Ti50Ni20Cu20Al10, Cu60Zr30Ti10, Fe56Co7Ni7Zr10B20, Ni60Nb20Ti12.5Zr7.5, Ti55Zr20Ni25 and Zr55Ti25Ni20. Milling parameters such as milling speed, ball to powder weight ratio have been varied over wide ranges in order to have a wide range of milling energies. The results indicate that total energy of milling has a decisive role than the impact energy of the ball in the formation of the amorphous phase by planetary ball mill. The paper compares the glass forming abilities of the various bulk glass forming compositions in terms of the milling maps in order to develop better understanding of glass forming criteria by mechanical alloying. © 2007 Elsevier B.V. All rights reserved.

Journal of Alloys and Compounds

On the conditions for the synthesis of bulk metallic glasses by mechanical alloying

In the present investigation, thermodynamic and topological concepts have been used together to understand the formation of bulk metallic glasses. The article attempts to develop a parameter that combines chemical mixing enthalpy (ΔH chem), mismatch entropy normalized by Boltzmann constant (ΔSσ /kB), and configurational entropy (ΔS config/ R), which can be effectively used to identify the best bulk glass forming compositions in multicomponent systems. The ΔHchem for multicomponent systems has been calculated by extending the Miedema's macroscopic model, and ΔSσ/kB was obtained from Mansoori's approach. The iso-ΔHchem, iso-ΔSσ /kB, and iso-ΔSconfig/R contours have been developed. The product of ΔHchem and ΔSσ/kB in the ΔSconfig /R range of 0.9 to 1.0 can be correlated strongly to glass forming ability. This has been demonstrated in the case of the quaternary Cu-Zr-Ti-Ni bulk glass forming system to determine the bulk metallic glass forming compositions. Mechanical alloying is used to prepare the bulk amorphous powder at the compositions predicted by the model in order to validate the model. © The Minerals, Metals &amp; Materials Society and ASM International 2007.

Thermodynamic and topological modeling and synthesis of Cu-Zr-Ti-Ni-Based bulk metallic glasses by mechanical alloying

A new parameter has been proposed to assess the glass forming ability of liquids and its effectiveness is compared with the existing parameters. The new parameter (α = Tx/Tl), which incorporates both the factors of stability of the liquid (a low Tl) and the thermal stability of glass (a high Tx), has good correlation with the critical cooling rate for glass formation in a wide variety of glass forming alloys. This parameter can even be used for those glass forming alloys, which do not show a clear glass transition temperature. It has also been shown that the heating rate used during differential scanning calorimetry has negligible effect on the different glass forming parameters. © 2005 Elsevier B.V. All rights reserved.

Journal of Non-Crystalline Solids

On the parameters to assess the glass forming ability of liquids

Heating and cooling rate dependence of the parameters representing the glass forming ability in bulk metallic glasses

Applied Physics Letters

Parameter for glass forming ability of ternary alloy systems

Gibb’s free energy for the crystallization of glass forming liquids

A topological model for metallic glass formation

Identification of compositions with highest glass forming ability in multicomponent systems by thermodynamic and topological approaches

Journal	Materials Science and Engineering A
ISSN	09215093
Open Access	No