Effective Method to Enhance the Glass-Forming Ability of Vitreloy 105 Containing High Oxygen Concentrations
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BULK metallic glasses (BMG) are metallic materials without long-range atomic ordering. Their amorphous structure is obtained by rapid cooling of the alloy melt. As a result, their physical, chemical, and mechanical properties are distinct from conventional crystalline alloys, showing high hardness,[1] large elastic strain,[2] high fracture and fatigue strength,[3] excellent corrosion, and wear resistance.[4] There are several BMG forming systems such as Fe-, Zr-, and Ti-based. Fe-based BMGs are mainly used due to their magnetic properties,[5] Ti-based due to their biocompatibility and corrosion resistance,[6] and Zr-based BMGs, subject of this work, show higher glass-forming ability (GFA) and higher mechanical properties compared to other systems.[7–9]
NELSON DELFINO DE CAMPOS NETO, RENAN FREIRE DE CARVALHO LOPES ROCHA, FLAVIO SOARES PEREIRA, CAROLINA SOARES, FELIPE HENRIQUE SANTA MARIA and MARCELO FALCA˜O DE OLIVEIRA are with the Department of Materials Engineering, Sa˜o Carlos School of Engineering, University of Sa˜o Paulo, Joa˜o Dagnone Avenue, 1100, Jardim Santa Angelina, Sa˜o Carlos, SP 13563-120, Brazil. Contact e-mail: nelson.delfi[email protected] Manuscript submitted November 6, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
The production of Zr-based BMGs is not an easy task once the alloy’s GFA is deteriorated by the contamination of elements which help the heterogeneous nucleation of crystalline phases. Oxygen, in this case, is of particular concern. Apart from the studies regarding the use of crystalline phases to form amorphous metallic matrix composites, researches investigate ways to mitigate the deleterious effects of the oxygen upon the glass formation using high-purity raw materials (> 99.999 pct purity), enhancing the control of the melting atmosphere, or by microalloying. Controlling the raw material and the melting atmosphere entails a very high cost in the production,[10] which makes the use of these alloys unfeasible. The microalloying is focused on elements that form more stable oxides compared to the Zr oxides, as the case of the rare earth elements. Yttrium is one of the most studied and successful elements for the improvement of the GFA in oxygen-contaminated Zr-based BMGs. It has been reported that Y prevents the precipitation of crystalline phases such as Zr2Cu and Zr4Ni2O,[11] improves the alloy glass-forming ability, and scavenges the oxygen from the melt forming innocuous oxides embedded in the amorphous matrix. Many of these reports clearly show that Y has an optimum concentration to enhance the glass-forming ability, above such optimum concentration, the GFA is deteriorated with the appearance of many undesirable
crystalline phases.[12] It is also worth noticing that such optimum Y concentration largely varies regarding many reports.[7,12–15] In this work, we depart from the hypothesis that Y best concentration occurs when it is almost totally consumed to form Y2O3 in the molten alloy leaving a minimum amount of both Y and O in the amorphous matrix. If it is true, one should
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