On the ternary eutectic reaction in the Fe 60 Cr 8 Nb 8 B 24 quaternary alloy Y. Guo a, * , A. Moreira Jorge Jr. a , C.S. Kiminami a , C. Bolfarini a , W.J. Botta a a Universidade Federal de S~ ao Carlos, Departamento de Engenharia de Materiais, Rod. Washington Luís, km 235, CEP 13565-905, S~ ao Carlos, SP, Brazil article info Article history: Received 30 July 2016 Received in revised form 1 November 2016 Accepted 21 November 2016 Available online xxx Keywords: Phase evolution Crystallography Thermodynamic calculation Ternary eutectic Convergent beam electron diffraction abstract Recently a Fe 60 Cr 8 Nb 8 B 24 quaternary amorphous/nanocrystalline composite coating has been success- fully synthesized by high velocity oxygen fuel in our group. The composite coating shows excellent wear and corrosion resistance. In order to understand the phase evolution of the quaternary alloy during cooling and interpret its good glass forming ability, the stable phases in the as-melted ingot of the same composition were studied by X-Ray diffraction, scanning electron microscopy, transmission electron microscopy and differential scanning calorimetry. Thermodynamic calculation was performed based on a database compiled from literature. The calculated results show good agreement with the microstructural observation. It was found that Fe 60 Cr 8 Nb 8 B 24 alloy lies very close to the eutectic point of the system, which is related to its high glass forming ability. The thermodynamic calculation could provide insightful understanding and guidance for the future amorphous composition designing in Fe-Cr-Nb-B quaternary system. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Due to its relatively small critical size, metallic glass might be difficult to be used as bulk structural material [1]. However, the size limitation is not a problem for protective coating. The Fe-based amorphous coating has received increasing attention due to its low cost and good glass forming ability [2e8]. Moreover, because of its excellent corrosion and wear resistance [9e14], the Fe-based amorphous coating could find its application in oil and petroleum industry. The Fe-Nb-B ternary phase diagram shows that the ternary system contains many high melting temperature borides [15,16]. High melting temperature indicates strong bonding be- tween component elements, which could be related to high hard- ness of the material. Particularly, in Nb-B binary system, the high melting temperature borides possess very high hardness, e.g. NbB 2 HV 2600, Nb 3 B 4 HV 2290, NbB HV 2200 and Nb 3 B 2 HV 1720 [17]. These hard borides are very interesting for the enhancement of wear resistance. In addition, it has been shown by our previous research that addition of Cr in the aforementioned Fe-Nb-B ternary system can improve its corrosion resistance in NaCl, acid and alkaline solutions [9,10]. A Fe 60 Cr 8 Nb 8 B 24 quaternary alloy was recently designed and successfully vitrified by melt spinning. The ribbon shows excellent glass forming ability and possesses a supercooled liquid region as large as 60 K [3]. Its onset glass transition temperature and crys- tallization temperature is as high as 615  C and 675  C, respectively. The coating of the same composition was fabricated by various techniques, including spray deposition [3], low velocity oxygen fuel (LVOF) [3] and high velocity oxygen fuel (HVOF) [18] in our group. It was found that the HVOF coating exhibits largest volume fraction of amorphous phase (up to 66%) and shows excellent wear and corrosion resistance due to the amorphous/nanocrystalline com- posite structure [18]. In contrary to the above fruitful results, the reason why Fe 60 Cr 8 Nb 8 B 24 quaternary alloy is a good glass former remains unknown. It has been shown that it is easier to obtain metallic glass if the composition locates close to the eutectic point of the alloy system, where the liquid could be kept as low temperature as possible and facilitates the formation of glass [1,19]. In order to find out the possible eutectic transformation, the phase diagram of the current system is required. However, there is not quaternary phase diagram reported for Fe-Cr-Nb-B in the literature. In the present study, we assume that small portion of Cr addition could be considered the same as Fe, and the quaternary system could be reduced to ternary Fe-Nb-B, for which a few phase diagrams have been reported. The assumption is based on the fact that Fe and Cr form solid solution at elevated temperature as shown in the Fe-Cr binary phase diagram [20], exhibit similar atomic size and similar chemical properties [21]. In fact, the small addition of Cr in the alloy is expected to enhance its corrosion resistance [10], * Corresponding author. E-mail address: yaofeng@dema.ufscar.br (Y. Guo). Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom http://dx.doi.org/10.1016/j.jallcom.2016.11.293 0925-8388/© 2016 Elsevier B.V. All rights reserved. Journal of Alloys and Compounds xxx (2016) 1e6 Please cite this article in press as: Y. Guo, et al., On the ternary eutectic reaction in the Fe 60 Cr 8 Nb 8 B 24 quaternary alloy, Journal of Alloys and Compounds (2016), http://dx.doi.org/10.1016/j.jallcom.2016.11.293