Microstructure of directionally solidified Ti–Fe eutectic alloy with low interstitial and high mechanical strength R.J. Contieri a , E.S.N. Lopes a , M. Taquire de La Cruz a , A.M. Costa b , C.R.M. Afonso c , R. Caram a,n a University of Campinas, School of Mechanical Engineering, Rua Mendeleyev, 200, 13083-860 Campinas, SP, Brazil b University of S ~ ao Paulo, School of Engineering in Lorena, Brazil c Federal University of S ~ ao Carlos, Department of Materials Engineering, Brazil article info Article history: Received 10 May 2011 Received in revised form 5 July 2011 Accepted 14 July 2011 Communicated by T. Nishinaga Available online 30 July 2011 Keywords: A1. Directional solidification A1. X-ray diffraction A1. Eutectics A1. Optical microscopy B1. Titanium compounds B1. Alloys abstract The performance of Ti alloys can be considerably enhanced by combining Ti and other elements, causing an eutectic transformation and thereby producing composites in situ from the liquid phase. This paper reports on the processing and characterization of a directionally solidified Ti–Fe eutectic alloy. Directional solidification at different growth rates was carried out in a setup that employs a water- cooled copper crucible combined with a voltaic electric arc moving through the sample. The results obtained show that a regular fiber-like eutectic structure was produced and the interphase spacing was found to be a function of the growth rate. Mechanical properties were measured using compression, microindentation and nanoindentation tests to determine the Vickers hardness, compressive strength and elastic modulus. Directionally solidified eutectic samples presented high values of compressive strength in the range of 1844–3000 MPa and ductility between 21.6 and 25.2%. & 2011 Elsevier B.V. All rights reserved. 1. Introduction Structural materials such as commercially pure (CP) titanium and its alloys are extremely important in a number of sectors, particularly in the transport, chemical, energy generation and biomaterial industries [1–5]. Although CP titanium possesses interesting properties, especially a good strength-to-weight ratio, high biocompatibility and enhanced corrosion resistance, its mechanical strength is relatively limited. However, its mechanical properties can be enhanced by alloying it with other elements. The mechanical behavior of the resulting alloys depends on the amount and type of alloying elements and processing routes applied. In this context, the performance of a structural material can be improved considerably by tailoring its microstructural morphology and the nature of its stabilized phases. An approach to optimize structural materials involves combin- ing Ti and other elements, which leads to an eutectic transforma- tion and results in the in situ production of composites from the liquid phase [6]. In situ composites obtained by directional solidification processing of eutectic alloys have more attractive and special characteristics than their constituent phases. In this technique the eutectic liquid phase decomposition is used to produce two or more solid phases, which results in a refined microstructure whose phases are arranged side by side [7]. Eutectic transformation in the Ti–Fe system can be employed to produce in situ composite materials whose enhanced mechan- ical strength renders them potentially interesting structural materials. In composite materials obtained by eutectic solidifica- tion, the matrix is reinforced by means of eutectic precipitation. In these cases, the eutectic structure is composed of regularly dispersed reinforcing phase incorporated into the matrix. Accord- ing to the Ti–Fe phase diagram shown in Fig. 1 [8] an eutectic phase transformation occurs at 1085 1C of a material with a composition of 32.5 wt% Fe whose liquid solidification gives rise to bTi solid solution phase and TiFe intermetallic compound. TiFe is stable at room temperature–1317 1C and presents a Pm-3m structure similar to that of CsCl, with a lattice parameter of a ¼0.2975 nm. The periodicity of the eutectic array depends on aspects of the growth of its solid phases and of solute fluxes across the solid/liquid interface [7]. Experimental results of the microstructure and mechanical properties of as-cast Ti–Fe revealed a mechanical strength of 2.2 GPa and ductility of 6.7%, with a microstructure composed of TiFe intermetallic compound and bTi phase [9]. Recent attempts to improve the mechanical behavior of Ti–Fe alloy have focused on the addition of alloying elements to this binary eutectic alloy. The effect of the addition of Sn to the Ti–Fe eutectic on its mechanical strength and ductility was investigated by Das et al. Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jcrysgro Journal of Crystal Growth 0022-0248/$ - see front matter & 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2011.07.007 n Corresponding author. Tel.: þ55 19 3521 3314; fax: þ55 19 3289 3722. E-mail address: rcaram@fem.unicamp.br (R. Caram). Journal of Crystal Growth 333 (2011) 40–47