Effects of dopants on the glass forming ability in Al-based metallic alloy

Abstract

The effect of dopants on the metallic glass forming ability is usually considered based on the analysis of changes in the liquid structure or thermodynamics. What is missing in such considerations is an analysis of how a dopant changes the properties of the crystal phases which can form instead of the glass. In order to illuminate this aspect we performed molecular dynamics simulations to study the effects of Mg and Sm dopants on the crystal nucleation in Al. The simulation data were found to be consistent with the experimental observations that addition of Mg to Al does not lead to vitrification but addition of only 8% Sm does. The significant effect of Sm doping was related to the intolerance of Al to this dopant. This leads to increase in the solid-liquid interfacial free energy, and therefore, to increase in the nucleation barrier and to a dramatic decrease in the nucleation rate. The intolerance mechanism also significantly affects the growth kinetics.The effect of dopants on the metallic glass forming ability is usually considered based on the analysis of changes in the liquid structure or thermodynamics. What is missing in such considerations is an analysis of how a dopant changes the properties of the crystal phases which can form instead of the glass. In order to illuminate this aspect we performed molecular dynamics simulations to study the effects of Mg and Sm dopants on the crystal nucleation in Al. The simulation data were found to be consistent with the experimental observations that addition of Mg to Al does not lead to vitrification but addition of only 8% Sm does. The significant effect of Sm doping was related to the intolerance of Al to this dopant. This leads to increase in the solid-liquid interfacial free energy, and therefore, to increase in the nucleation barrier and to a dramatic decrease in the nucleation rate. The intolerance mechanism also significantly affects the growth kinetics.

Crystal growth rates in supercooled atomic liquid mixtures

“…The crystallization behavior of supercooled binary alloys is of particular importance, not only because of their great technological relevance, but also for studies of glass-forming ability in few-components liquids [2,3]. Simulations do show that crystal growth rates in binary alloys can be much lower than those predicted by the CL model [1,7,11,12], but the WF model also fails to describe crystal growth in these systems [7,9]. The current situation is that there is no comprehensive theory that is able to explain such differences in crystal growth rates arising in entirely metallic liquids [2,3].…”

“…where the explicit expression of Φ is derived in Methods, see Eq. (12). Note that ν CL (T ) = ν CL (T )…”

“…However, many crystal growth rates are difficult to treat with these classical models, especially when key variables such as composition and particle size ratio are varied in binary systems [1,[6][7][8][9][10][11][12]. The crystallization behavior of supercooled binary alloys is of particular importance, not only because of their great technological relevance, but also for studies of glass-forming ability in few-components liquids [2,3].…”

Revealing hidden supercooled liquid states in Al-based metallic glasses by ultrafast scanning calorimetry: Approaching theoretical ceiling of liquid fragility

“…Consequently, it is more difficult to develop Al-MGs than other MGs. Fundamentally, it remains to be a puzzling issue why the Al-MGs are so unique [27,30,36].Among several factors, one clue for the distinction between bulk glasses and marginal glass formers is based upon their supercooled liquids [19,23,26,27]. The change of the relaxation dynamics (e.g., viscosity, diffusivity or relaxation time) with the temperature is highly materialspecific.…”

“…Consequently, it is more difficult to develop Al-MGs than other MGs. Fundamentally, it remains to be a puzzling issue why the Al-MGs are so unique [27,30,36].…”