Abstract
The effect of yttrium additions on the glass formation of the Zr50Cu40Al10 alloy with high oxygen content was investigated. Unlike other reports showing the positive effect of alloying Zr-based alloys with a few percent of rare earth elements, we examined the Y-to-oxygen ratios. As calculated, a stoichiometric amount of yttrium (2808 at ppm) is required to bind all the oxygen (4212 at ppm) to form the Y2O3. Additionally, the influence of half (1404 at ppm) and double stoichiometric (5616 at ppm) levels of yttrium, with respect to the measured oxygen content to be bound was evaluated. The Y-doped alloys were synthesized by arc melting, followed by suction casting into copper molds with conical and rod cavities. The critical diameter of the undoped alloy was below 3 mm, while stoichiometric and double stoichiometric yttrium concentrations allowed to obtain 5 and 7 mm diameter glassy samples, respectively. Microstructure observations confirmed the scavenging effect of yttrium, leading to the formation of a cubic ( Iabar{3} space group) yttrium sesquioxide. The glass forming ability of the alloys was additionally determined based on differential thermal analysis, allowing to propose the best indicator for the studied Zr-Cu-Al alloys.
Highlights
ZR-BASED bulk metallic glasses (BMGs) belong to the group of modern metallic materials
We systematically studied the effect of yttrium additions to the Zr50Cu40Al10 alloy, with high oxygen content, on its glass-forming ability
Similar oxides were observed in the case of double stoichiometric amount of yttrium with respect to the measured oxygen content to be bound (B4/3)
Summary
ZR-BASED bulk metallic glasses (BMGs) belong to the group of modern metallic materials The fabrication of such materials, i.e., obtaining an amorphous structure, requires sufficiently fast cooling rates during solidification to bypass the crystallization process. Special attention must be paid to oxygen content, as this element dramatically reduces the alloy’s glass forming ability (GFA) and deteriorates its mechanical properties.[4,5,6,7,8] Such a dramatic drop in the GFA is caused by the formation of oxides or other oxygen-induced inclusions, acting as perfect heterogeneous nucleation sites during solidification.[9,10,11,12] The ZrO2 oxide is regarded as a nucleation catalyst in Zr-based alloys. This oxide exists in three crystallographic forms: monoclinic a ZrO2, which is thermodynamically stable up to 1478 K, tetragonal b ZrO2 stable between 1475 K and 2650 K, and cubic c ZrO2 (CaF2—type) phase, which is stable up to the melting point, 2983 K.[13]
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