Effect of zirconium addition on the phase transformations in as-cast and heat-treated Ti–Zr–Si–B alloys Alfeu Saraiva Ramos a,⇑ , Carlos Angelo Nunes b , Geovani Rodrigues c , Erika Coaglia Trindade Ramos a a Universidade Federal de Alfenas, Instituto de Ciência e Tecnologia, Rodovia José Aurélio Vilela, 11999, 37715-400 Poços de Caldas, MG, Brazil b Universidade de São Paulo, Departamento de Engenharia de Materiais, Polo Urbo-Industrial, Gleba AI-6, Mondesir, s/n, Polo Urbo-Industrial Gleba AI-6, 12600-970 Lorena, SP, Brazil c Universidade Federal de Itajubá, Instituto de Engenharia Mecânica, Avenida BPS, 1303, Pinheirinho, 37500-903 Itajubá, MG, Brazil article info Article history: Received 25 April 2013 Received in revised form 8 February 2014 Accepted 27 February 2014 Available online 12 March 2014 Keywords: Metals and alloys Microstructure Phase diagrams Scanning electron microscopy SEM abstract This work reports on effect of zirconium addition on the phase transformations in as-cast and heat-trea- ted Ti–6.7Zr–22.2Si–11.1B, Ti–7Zr–15Si–7.5B, Ti–7Zr–10Si–5B, Ti–7Zr–7.5Si–15B and Ti–7Zr–30Si–5B alloys (at.%). After arc melting, these Ti–Zr–Si–B alloys were heat-treated at 1200 °C for 90 h. Samples of as-cast and heat-treated Ti–Zr–Si–B alloys were evaluated by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry, and wavelength X-ray dispersive spectrometry. Nanosized eutectic structure constituents were observed in microstructures of as-cast Ti–Zr–Si–B alloys. Ti SS (ss- solid solution), Ti 6 Si 2 B, TiB and Ti 5 Si 3 dissolved up to 5.3, 14.2, 1.5 and 11.6 at.% Zr, respectively, which is in agreement with the shift of their peaks toward smaller diffraction angles. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction As-cast Ti–Si and Ti–Zr–Si alloys, which contain structures con- stituted by primary precipitates of Ti SS (ss-solid solution) uni- formly dispersed in eutectic matrixes formed by the Ti SS and Ti 5 Si 3 phases, present attractive mechanical properties and oxida- tion resistance [1–7]. In ternary alloys, the added zirconium dis- solves in these two phases [1,7]. However, the formation of Ti 5 Si 3 grains leads to crack formation due to its high thermal expansion coefficients and anisotropy [4,8]. Various works reported on the ternary phase diagram of the Ti– Zr–B system [9–13]. Samples of composition (at.%) Ti–13Zr–8B and Ti–31Zr–9B were two-phased with primary metal monoboride grains in a metal–metal monoboride eutectic [9]. The maximum exchange of zirconium for titanium in titanium monoboride was approximately 9 at.% [9,10]. Solubility of boron is small in both individual metals as well as in the ternary alloys [9]. Recent studies on the Ti–Si–B system have confirmed the exis- tence of a new ternary phase with stoichiometry close to Ti 6 Si 2 B in both as-cast and heat-treated Ti–Si–B alloys [8,14–17]. The compo- sition region in which the Ti 6 Si 2 B-primary grains are formed is lo- cated in the Ti ss + Ti 6 Si 2 B + Ti 5 Si 3 three-phase field, as well as the composition of the ternary invariant eutectic L , Ti ss + Ti 6 Si 2- B + Ti 5 Si 3 . The crystallographic studies revealed that this ternary phase possesses hexagonal unit cell, space group P-62m, lattice parameters a = 6.803 Å and c = 3.337 Å, and it is isomorphic to the Ni 6 Si 2 B phase [14]. Ti 6 Si 2 B exhibits an enthalpy of formation at 0 K of – 62.5 kJ/mol of atoms and its electronic density of states was determined [17]. With respect to the thermal expansion coef- ficients, the Ti 6 Si 2 B compound exhibits a a = (9.7 ± 0.2)10 À6 K À1 and a c = (9.6 ± 0.6)10 À6 K À1 while for Ti 5 Si 3 a a = (5.9 ± 0.2)10 À6 K À1 and a c = (16.9 ± 0.6)10 À6 K À1 for [8]. The details on the primary region of Ti 6 Si 2 B precipitation as well as the monovariant lines L + Ti SS + TiB, L + Ti SS + Ti 6 Si 2 B, L + Ti 5 Si 3 + Ti 6 Si 2 B and L + Ti 6 Si 2 B + TiB pre- sented in the Ti–Si–B liquidus surface projection were carefully established from the experimental results after analyzing several different alloy compositions [14]. No experimental information was found in literature on phase transformations in Ti–Zr–Si–B alloys. Based on the Ti–Si–B alloys previously studied in [14], this work discusses on the effect of zirconium addition on the phase transformations in as-cast and heat-treated Ti–Zr–Si–B alloys. 2. Materials and methods The following starting materials were used to prepare the Ti–6.7Zr–22.2Si– 11.1B, Ti–7Zr–15Si–7.5B, Ti–7Zr–10Si–5B, Ti–7Zr–7.5Si–15B and Ti–7Zr–30Si–5B (at.%) alloys by arc melting and subsequent heat treatment at 1200 °C for 90 h: Ti (min 99.7 wt%), Zr (min 99.5 wt% Zr with up to 4.5 wt% Hf), Si (99.999 wt%), and http://dx.doi.org/10.1016/j.jallcom.2014.02.179 0925-8388/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +55 35 36974711. E-mail addresses: alfeu.ramos@unifal-mg.edu.br (A.S. Ramos), cnunes@demar. eel.usp.br (C.A. Nunes), grodrigues@unifei.edu.br (G. Rodrigues), erika.ramos@ unifal-mg.edu.br (E.C.T. Ramos). Journal of Alloys and Compounds 601 (2014) 94–99 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom