Microstructural characterization of as-cast Co–B alloys M.I.S.T. Faria a, ⁎ , T. Leonardi a , G.C. Coelho a , C.A. Nunes a , R.R. Avillez b a Faculdade de Engenharia Química de Lorena (FAENQUIL), Departamento de Engenharia de Materiais (DEMAR) Pólo Urbo Industrial, Gleba AI-6, C.P. 116, 12600-970 Lorena-São Paulo-Brazil b Pontifícia Universidade Católica do Rio de Janeiro-DCMM-PUC-Rio Rua Marques de São Vicente, 225 CEP: 22453-900-Gávea-Rio de Janeiro-Brazil Received 10 February 2006; received in revised form 31 May 2006; accepted 31 May 2006 Abstract This work presents results of microstructural characterization of as-cast Co–B alloys. Samples of different compositions were prepared by arc melting Co (min. 99.97%) and B (min. 99.5%) under argon atmosphere in a water-cooled copper crucible with non-consumable tungsten electrode and titanium getter. All samples were characterized by scanning electron microscopy (SEM) in back-scattered electron (BSE) mode, X-ray diffraction (XRD) and wavelength dispersive spectrometry (WDS). A good agreement is observed between the obtained microstructures and those expected by the currently accepted Co–B phase diagram. © 2006 Elsevier Inc. All rights reserved. Keywords: Co–B system; Phase diagram; Borides; Solidification 1. Introduction Materials containing Co, Si and B in their composi- tions, may form an amorphous microstructure when submitted to rapid solidification, the resulting material presenting good magnetic and favorable mechanical and corrosion properties [1–3]. The determination of the phase relations of the Co–Si–B system is fundamental for the development of these materials. We are investi- gating the liquidus projection of the Co–Si–B system, for which the knowledge of the solidification pathway of the alloys, based on the interpretation of as-cast micro- structure, is necessary. In a previous work [4] we have reported results on the microstructural characterization of as-cast Co–Si alloys and in this work a similar study concerning the Co–B system is presented. The informa- tion from this investigation also contributes to the evaluation of the Co–B phase diagram. The currently accepted Co–B phase diagram, shown in Fig. 1 [5], is based on the work of Schobel and Stadelmaier [6] and incorporates solubility data of B in Co reported by Lerner and Cadeville [7]. The Co–B system consists of three intermediate compounds, Co 3 B, Co 2 B and CoB, the terminal solid solutions (αCo), (εCo) and (βB), as well as the liquid phase L. The solubility limits of the terminal solid solutions are negligible, as well as the homogeneity range of the intermediate com- pounds [6,7]. The crystallographic data of the stable solid phases are shown in Table 1 [5,9]. 2. Experimental procedure The alloy compositions produced in this work were prepared from pure Co (min. 99.97%) and B (min. Materials Characterization 58 (2007) 358 – 362 ⁎ Corresponding author. E-mail address: ismenia@phase.faenquil.br (M.I.S.T. Faria). 1044-5803/$ - see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.matchar.2006.05.014