Effect of Yttrium Additions in Relation to Oxygen Content on Glass Formation in the Zr50Cu40Al10 Alloy

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 ($$ Ia\bar{3} $$ I a 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.

The Scavenging Effect of Different Rare-Earth Elements in the Low-Purity Zr50Cu40Al10 Alloy

“…In our previous works, the oxygen content in the Zr50Cu40Al10 alloy was 918 wt. ppm [19,36]. Here, a slightly higher value (988 wt.…”

“…However, the biggest disadvantage of this method is heat distribution disturbance caused by potential turbulent liquid flow during casting. Laws et al [42] showed that the real critical casting diameter obtained from parallel-edged molds should be lower than those from conical molds, however, our previous works show a reverse correlation [19,36,43]. This effect can be stronger in the case of inclusion occurrence (e.g.…”

“…II, but these should be treated as qualitative analysis, rather than quantitative, because of small size of precipitates. Due to the different atomic numbers of REE forming oxides, those containing Sc and Y (shown in [36]) give dark contrast in the BSE mode in the matrix, while oxides containing Lu, Gd and Nd are bright. EDX results of the REOs (spots 1, 4, 7, 9) confirmed increased oxygen levels.…”

“…It should be noted that DTA analysis was carried out at a constant heating rate of 20 K/min, so the phase transformations are shifted to higher temperatures compared to the ND patterns. In the LO sample, the CuZr2 phase (tetragonal, I4/mmm) appeared along with the AlCu2Zr (cubic, 𝐹𝑚3 ̅ 𝑚) and transition phase [35,36]. The crystallization onset temperature for the HO sample is about 20 K lower compared to the LO alloy, and the Zr6Al7Cu16 phase (triclinic, P1) was identified instead of the AlCu2Zr.…”

“…The use of purely monoclinic REOs is problematic as they are formed by elements with low boiling points (Sm and Eu) or by radioactive elements (Pm), therefore they were not studied here. In our previous works [19,36], efforts were made to characterize and enhance the GFA in the Zr50Cu40Al10 alloy through Y additions. It was found that the critical diameter Dc (diameter with a maximum amorphous thickness) strongly depends on the oxygen content, and the proper Y doping of a low purity (high oxygen) alloy allows to obtain a similar Dc value (improved from 3 mm to 7 mm) as in the high purity (low oxygen) alloy (8 mm).…”