Abstract
Herein, we elucidate how to accurately quantify glass-forming ability (GFA) by measuring effective volume relaxation of supercooled melt. We propose a new parameter, denoted as κ, for representing the relaxation, which is calculated by combining temperature-dependent changes of normalized specific volume reflecting relative volume relaxation with the normalized temperature range reflecting the relative position of the C curve in a Time-Temperature-Transformation (TTT) diagram. The interrelationship between the κ parameter and critical cooling rate is elaborated by measuring V-T diagrams and TTT diagrams of Zr55Co26Al19 and Zr46Cu30.14Al8Ag8.36Be7.5 glass-forming alloys and discussed in comparison with representative GFA parameters reported up to date. These results would give us a guideline on how to precisely evaluate GFA by linking volumetric aspect to thermodynamic and kinetic aspects for glass formation and help develop customized glass-forming alloys as well as a highly precise control of glass formation process.
Highlights
From the early stage of the discovery of metallic glasses, it was noticed that liquid viscosity plays an important role in glass-forming ability (GFA), which governs the crystallization kinetics of undercooled melt and the critical cooling rate (Rc) for vitrification.1,2 In the same vein, the Cohen-Grest model suggests a correlation between free volume and viscosity.3 The free volume of a liquid affects the packing density and mobility of atoms
Numerous criteria have been proposed to guide the alloy design with high GFA,[8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29] which can be broadly classified into the three categories of thermodynamic, kinetic, and structural aspects for glass formation depending on the factors that are primarily viewed as decisive in the formation of amorphous phase
A GFA indicator (κ parameter) has been proposed by combining the temperature range reflecting the relative position of the C curve in the Time-TemperatureTransformation (TTT) diagram and the temperature-dependent change of normalized specific volume reflecting relative volume relaxation
Summary
From the early stage of the discovery of metallic glasses, it was noticed that liquid viscosity plays an important role in glass-forming ability (GFA), which governs the crystallization kinetics of undercooled melt and the critical cooling rate (Rc) for vitrification.1,2 In the same vein, the Cohen-Grest model suggests a correlation between free volume and viscosity.3 The free volume of a liquid affects the packing density and mobility of atoms. S. Park1,b 1Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826, South Korea 2Korea Research Institute of Standards and Science, Daejeon 34113, South Korea 3Department of Nano Science, University of Science and Technology, Daejeon 34113, South Korea (Received 7 August 2017; accepted 22 September 2017; published online 12 October 2017)
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