Melt fluxing to elevate the forming ability of Al-based bulk metallic glasses

Abstract

Salt-fluxing treatment is an effective technique to improve the glass-forming ability (GFA) of bulk metallic glass (BMG)-forming melts, as demonstrated before in Pd- and Fe-based systems. However, it has been challenging to develop similar fluxing protocol for more reactive melts, such as Al-rich BMG-forming systems. Here we design new fluxing agents, from a thermodynamics perspective that takes into account combined effects of physical absorption and chemical absorption (reaction) between the fluxing agents and oxide inclusions. MgCl2-CaCl2 composite salts were selected, and their fluxing effects were systematically studied on an Al86Ni6.75Co2.25Y3.25La1.75 alloy, the best BMG-forming composition reported thus far for Al-rich alloy systems. The oxygen content was found to continuously decrease in the master alloy with increasing cycles of salt-fluxing treatment, with chlorate products on the surface suggesting concurrent physical absorption and chemical reaction. The fluxing treatment developed has enabled a record critical size (diameter) of 2.5 mm for Al-based BMGs. Our finding is thus an advance in developing highly desirable Al-based BMGs, and also provides guidance for designing processing protocol to produce larger-sized BMGs in other reactive systems.

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

“…25 La 1.75 with a fully glassy rod of 1.5 mm in diameter. Although the glassy rod can reach 2.5 mm for the same composition after a refined fluxtreatment of the liquid [31], this critical size is still much smaller than those of typical Zr-based MGs (~75 mm) [32], Mg-MGs (25 mm) [18] and Pd-MGs (80 mm) [33]. Moreover, the glass forming ability of Al-MGs is very sensitive to compositions.…”

“…However, one remarkable exception is the family of Al-based MGs [23,24]. Although there have been continuous efforts in optimizing compositions and improving processing techniques since its first discovery [29] several decades ago, the glass forming ability of Al-MGs is still limited nowadays [23,30,31]. Recently, Wu et al [30] reported that the hitherto best glass forming ability for Al-MGs is from Al 86 Ni 6.75 Co 2.25 Y 3.…”

Glass-Forming Ability and Thermal Properties of Al70Fe12.5V12.5X5(X = Zr, Nb, Ni) Amorphous Alloys via Minor Alloying Additions

“…The hot working of amorphous powder needs better thermal stability and higher glass-forming ability (GFA), which needs to produce an excellent amorphous powder. Researchers have been a focused effort that aims to understand the effect of minor alloying additions on GFA and thermal stability and have proposed many theories on structure, thermodynamic and kinetic factors, so as to find out the rule of amorphous formation, optimize the composition design of amorphous alloy and find the amorphous alloy system which are beneficial to later application [5][6][7][8][9][10][11][12][13][14]. It is generally believed that the amorphous alloy system should contain three or more elements, the atomic size difference of the main components should generally be greater than 12% and with a large negative mixing enthalpy.…”

Preparation, Characterization, and Properties of Novel Ti-Zr-Be-Co Bulk Metallic Glasses

“…Thus, light-metal-based BMGs have attracted tremendous attention and research. In the past decades, many lightweight BMGs such as Al- [6,7], Mg- [8,9], and Ti-based BMGs [10][11][12][13][14] have been successfully developed. However, the main bottleneck of Al-based BMGs is the relatively low glass-forming ability (GFA) (the maximum critical diameter of only 1.5 mm [6]), while Mg-based BMGs always lack room temperature plasticity even upon compression [8,9].…”