Letter to the Editor Bulk metallic glasses based on ytterbium and calcium J.Q. Wang a , J.Y. Qin b , X.N. Gu c , Y.F. Zheng c , H.Y. Bai a, ⁎ a Institute of Physics, Chinese Academy of Sciences, Beijing 100190, PR China b Department of Physics, University of Science and Technology of China, Hefei 230026, PR China c Department of Advanced Materials and Nanotechnology, College of Engineering, Peking University, Beijing 100871, PR China abstract article info Article history: Received 8 July 2010 Received in revised form 25 October 2010 Available online 14 December 2010 Keywords: Metallic glass We report the formation of a family of bulk metallic glasses (BMGs) based on rare earth element of ytterbium and alkaline earth element of calcium. The glass-forming ability, atomic packing density and corrosion behaviors of the BMGs show an extremum around the eutectic point with the change of the concentration of Yb and Ca. © 2010 Elsevier B.V. All rights reserved. Bulk metallic glasses (BMGs) have caught attention and interests because of their excellent properties such as high strength near the theoretical prediction, large elastic strain, and good corrosion and wear resistances [1–3]. The promising applications as mechanical structural materials, magnetic materials, bio-materials, and thermo- processable materials compel people to search new BMGs with good glass-forming ability (GFA) and novel properties [1–8]. It is recently found that the replacement of similar elements can obviously change the GFA and other properties [1,9,10]. Singularity phenomena and non-linear behaviors along with the change of compositions exist in various systems [9–14]. Among these singularities, the local symme- try [12], the atomic packing density [13], and liquid dynamic properties [14] have close relation with the mysterious glass-forming phenomenon. In this letter, we report the fabrication of a family of new bulk metallic glasses based on Yb and Ca. The glass-forming ability, reduced glass transition temperature (T rg ), thermal properties, mass density, and the corrosion properties are measured. It is found that these properties show non-linear relation with compositions and have an extremum around the eutectic point with the replacement of Yb by Ca. The series of Yb 62.5 -x Ca x Zn 20 Mg 17.5 (x = 2.5, 10, 20, 30, 40, 50, and 60) BMGs were cast into copper mold after induction melting of the base elements (purity better than 99.9 at.%) in a quartz tube under argon atmosphere. The amorphous states of the YbCa-based BMGs are testified by X-ray diffraction (XRD) in a MAC M03 XHF diffractometer (Cu K α radiation) and by a differential scanning calorimeter (DSC, Perkin-Elmer DSC-7) under purified argon at 10 K/min heating rate (details can be found in Ref. [15]). The mass density was determined by the Archimedean technique in ethanol liquid. The mass was measured using an analytical balance with an accuracy of 0.01 mg. The repeated measuring error (in both air and ethanol) was better than ±0.02 mg. Rod samples with the same size (2 mm in diameter) are adopted for the density measurement in order to rule out the cooling rate effect. The samples were prepared with weight bigger than 100 mg. So, the measuring error was better than 0.02%, and we can then track the changes of mass density with smaller experimental error. The polarization corrosion test was conducted in a 0.05 M Na 2 SO 4 electrolyte. A three-electrode cell was used for electrochem- ical polarization tests (details can be found in Ref. [16]). The counter electrode was made of platinum and the reference electrode was saturated calomel electrode (SCE). All potentials quoted were on the SCE scale. The samples for corrosion test were closely sealed with epoxy resin and only leave an end-surface (with a cross-section area of about 3 mm 2 ) exposed to the solution. Prior to the test, the testing surface of each sample was mechanically polished to 1000#, and then degreased in acetone, distilled water and dried in air. The potential dynamic polarization curves of the samples were recorded at a scan rate of 1 mV/s when the open-circuit potential became almost steady. Fig. 1(a) shows the XRD patterns of the Yb 62.5 - x Ca x Zn 20 Mg 17.5 (x = 2.5, 10, 20, 31.25, 40, 50, and 60) BMGs in diameter of 2 mm. The curves show a broad maximum characteristic without obvious crystalline sharp peaks, denoting good GFA of the systems. The DSC traces with obvious glass transition and crystallization behaviors at a heating rate of 10 K/min are shown in Fig. 1(b)–(c). The characteristic temperatures in details are listed in Table 1. The glass transition temperatures (T g ) decrease monotonously along with the increasing of Ca concentration and has a sharp drop around x = 40. The value of T g ranges from 345 K to 376 K, and all of them are near or lower than the boiling temperature of water (373 K). The crystallized tempera- tures (T x ) range from 399 K to 380 K. These data indicate that the YbCa-based BMGs are another metallic plastic system [17] and would be a good candidate in thermal-plastic applications. Fig. 1(c) shows the melting part of the DSC traces. The melting temperatures T m decrease monotonously from 650 K to 607 K. The liquid temperatures Journal of Non-Crystalline Solids 357 (2011) 1232–1234 ⁎ Corresponding author. E-mail address: hybai@aphy.iphy.ac.cn (H.Y. Bai). 0022-3093/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2010.11.046 Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/ locate/ jnoncrysol LETTER TO THE EDITOR