A new thermodynamic parameter PHSS (PHSS = ΔHC(ΔSσ/kB)(ΔS C/R)) is proposed, to describe and predict the glass forming ability (GFA) of Fe based alloys. Here ΔHC is the chemical enthalpy of mixing, ΔSσ is the mismatch entropy and ΔS C is the configurational entropy. The PHSS parameter incorporates enthalpy of mixing, size mismatch and the number of elements in the systems which influence GFA significantly. It was observed from rapid solidification processing (RSP) and mechanical alloying (MA) studies that, all alloys with PHSS in between -0.55 kJ/mol to -6.00 kJ/mol would form glass in the Fe-Zr-B system. MA and RSP experiments on multi-component Fe-Cr-Ni-Zr-B alloys indicated that PHSS is a better parameter to predict GFA of the system than PHS, a parameter used in earlier studies. It was also observed that bulk metallic glass (BMG) forming alloys can be observed in between a PHSS range of -3.00 kJ/mol to -6.00 kJ/mol, with the maximum thickness of the BMG increasing with decreasing PHSS within the above range. © 2012 Elsevier Ltd. All rights reserved.

Budaraju Srinivasa Murty

Department of Metallurgical and Materials Engineering

B. Ramakrishna Rao

M. Srinivas

Ashutosh S. Gandhi

Bulk metallic glass

CONFIGURATIONAL ENTROPY

Enthalpy of mixing

FE-BASED ALLOYS

GLASS-FORMING ABILITY

GLASSES , METALLIC

Iron-based

MECHANICAL ALLOYING AND MILLING

Multi-component systems

Multicomponents

RAPID SOLIDIFICATION PROCESSING

SIZE MISMATCH

Thermodynamic parameter

Alloys

Chromium

enthalpy

entropy

Forecasting

Glass

Mechanical Alloying

Metallic glass

Zirconium

Iron alloys

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IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Intermetallics

One of the major challenges in high entropy alloy (HEA) research is to obtain single-phase solid solutions by proper selection of components and processing techniques. Often one encounters situations where topologically close-packed (TCP) phases are present in the HEA microstructures. TCP phases are a class of intermetallic phases that are in general considered undesirable. The ability to predict these phases in HEAs using the Calphad (CALculation of PHAse Diagrams) method has been shown to accelerate the identification of promising compositions. In this review, an analysis of the reported Calphad studies and corresponding microstructural information on HEAs is done to evaluate the success of the Calphad method for TCP phases. A total of 52 alloys with 123 post-heat treatment microstructures reported so far have been compared. Challenges and issues in experiments and calculations are brought out with a possible way forward. © 2017, The Minerals, Metals &amp; Materials Society.

Topologically Close-packed Phase Formation in High Entropy Alloys: A Review of Calphad and Experimental Results

Identifying high entropy bulk metallic glasses (HEBMGs) through high entropy alloy philosophy has the potential to avert complications inherent to pinpointing bulk metallic glass forming compositions. Currently, the mixing enthalpy and topological strain parameter of a multicomponent alloy is a popular guideline to demarcate glass forming alloys from solid solution and intermetallic phase forming high entropy alloys. However, the discovered HEBMGs have relatively inferior glass forming ability (GFA) in comparison to the best glass former in a particular alloy system. The origin of such low glass forming ability can be traced back to their moderately higher liquidus temperature. Therefore there exists an opportunity to engineer non-equiatomic HEBMGs through modifying the composition of the constituent alloying elements. In this work, based on the thermodynamic modeling of two quinary alloy systems we demonstrate that the existence of large atomic size difference over broad compositional region is necessary condition for enhancing GFA in non-equiatomic HEBMGs. In addition, it is proposed that figuring out the prominent binary chemical interactions in the near equiatomic alloy composition is an effective approach to enhance GFA in these complex alloy systems. © 2016 Elsevier B.V.

Journal of Non-Crystalline Solids

Identifying non-equiatomic high entropy bulk metallic glass formers through thermodynamic approach: A theoretical perspective

Amorphization behavior in equiatomic high entropy alloys has been investigated. Pseudo-binary FeCrNi-M-B alloys and true equiatomic high entropy compositions FeCrNi-M-Si (M = Co, Mn, Nb, Ti, Zr) have been synthesized using mechanical alloying. Formation of amorphous phase has been confirmed using X-ray diffraction analysis and transmission electron microscopy. All alloys containing Si showed significant amorphization. Fe80B20 is known to be a good glass former, but no amorphous phase was observed in Fe-B based alloys except for FeCrNiNbB. The slower kinetics of dissolution of B in the alloy due to its sluggish diffusivity caused by its higher melting point is attributed to be the reason for the poor amorphization in B containing alloys. © 2015 Elsevier B.V.

Amorphization in equiatomic high entropy alloys

Abstract This work explores the idea of predicting metallic glass forming composition in a multi component alloy for which an equilibrium phase diagram is yet to be deciphered. Deep eutectic regions in a quaternary alloy (Zr-Ti-Cu-Ni) have been extrapolated to the quinary Zr-Ti-Cu-Ni-Al system for designing a potential bulk glass forming composition. P<inf>HSS</inf> parameter which is the product of mixing enthalpy, mismatch entropy and configurational entropy of an alloy, has been utilized for thermodynamic modeling. P<inf>HSS</inf> values are computed through substitution of Al into the each of the fifteen quaternary eutectics that have been reported in the literature in the Zr-Ti-Cu-Ni system. A good correlation of P<inf>HSS</inf> range between modeled alloys and established glass formers indicates the subtle efficacy of this method for high entropy amorphous alloy design through a rationale thermodynamic approach. © 2015 Elsevier Ltd

Thermodynamic modeling and composition design for the formation of Zr-Ti-Cu-Ni-Al high entropy bulk metallic glasses

In this paper, we report the effect of partially replaced Nb on glass forming ability (GFA), structure and soft magnetic properties in Fe86Zr7−xNbxB6Cu1 (x = 0 and 3.5 at.%) melt spun ribbons, processed at different cooling rates by varying wheel speeds. Decreasing the wheel speed, the structures of both alloys change from complete amorphous to partial amorphous then to complete crystalline phase. It has been found that the Nb enhances GFA which is also confirmed through thermodynamically calculated PHSS values. The annealing of completely amorphous ribbons of both compositions, processed at a wheel speed of 47 m/s leads to the formation of α-Fe phase in amorphous matrix and enhances soft magnetic properties. © 2015, The Indian Institute of Metals - IIM.

Transactions of the Indian Institute of Metals

Glass Forming Ability, Structure and Soft Magnetic Properties of Rapidly Solidified Fe86Zr7−xNbxB6Cu1 Alloy Ribbons

Based on the thermodynamic and topological approach, Cu60Zr 30Ti10 has been identified as the best bulk metallic glass forming composition in Cu-Zr-Ti system. Bulk metallic glass has been successfully produced using mechanical alloying of elemental blends and consolidation of the resulting glassy powders into pellets of 8 mm diameter. Dry sliding wear of glassy pellets at different annealed states showed that the relaxed metallic glass has excellent wear resistance. © (2011) Trans Tech Publications.

Materials Science Forum

Thermodynamic model and synthesis of bulk metallic glass in Cu-Zr-Ti system by mechanical alloying

Melt-spun ribbons of Fe99-x-y Zr x B y Cu1 alloys with x + y = 11 and x + y = 13 were prepared under similar experimental conditions and characterized for structure and soft magnetic properties. Substitution of Zr by B changes the structure of as-spun ribbons from completely amorphous to cellular bcc solid solution coexisting with the amorphous phase at intercellular regions and then to completely dendritic solid solution. The glass forming ability (GFA) of the Fe-Zr-B-Cu system, evaluated from thermodynamic properties such as enthalpy of mixing and mismatch entropy, is found to be in good agreement with the experimental observations. Annealing of all ribbons leads to the precipitation of nanocrystalline bcc α-Fe phase from both amorphous phase and already existing bcc solid solution. A window of alloy compositions that exhibit the best combination of soft magnetic properties (high saturation magnetization and low coercivity) was identified. © 2010 The Minerals, Metals &amp; Materials Society and ASM International.

Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

Structure, properties, and glass forming ability of melt-spun Fe-Zr-B-Cu alloys with different Zr/B ratios

A thermodynamic model parameter P H-S, which is a product of enthalpy of chemical mixing and mismatch entropy normalized by Boltzmann's constant, was used as a guiding tool to predict amorphous phase forming compositions in Fe-rich alloys of the Fe-Zr-B system. Attempts were made to evaluate the effect of Zr addition on the P H-S parameter and phase formation by mechanical alloying (MA) and rapid solidification processing (RSP). A systematic evaluation of the P H-S parameter of various binary compounds in the Fe-Zr-B system and ternary alloys indicated ∼-7 kJ/mol as a lower bound for the formation of amorphous phase. Model predictions were verified with phase formation in two random compositions in the Fe-rich end of the Fe-Zr-B system synthesized by MA and RSP. © 2011 The Minerals, Metals &amp; Materials Society and ASM International.

On prediction of amorphous phase forming compositions in the iron-rich Fe-Zr-B ternary system and their synthesis

Compositions with high glass forming ability have been identified in Zr-Cu-Al system with the help of a thermodynamic parameter, which takes into account the enthalpy of chemical mixing (ΔHchem), the mismatch entropy normalized by Boltzmann's constant (Sσ/kB) and the configurational entropy (Sconfig/R). The best bulk metallic glass forming composition is identified as the one at ΔHchem and Sσ/kB maxima in a specific range of Sconfig/R. A product of thermodynamic parameters (Δ Hchem × Sσ / kB) is found to have strong correlation with glass forming ability and can help to identify the exact composition that can form bulk metallic glass. © 2006 Elsevier Ltd. All rights reserved.

Optimization of bulk metallic glass forming compositions in Zr-Cu-Al system by thermodynamic modeling

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	Intermetallics
ISSN	09669795
Open Access	No