Mechanical properties of a two-phase amorphous Ni–Nb–Y alloy studied by nanoindentation A. Concustell, a, * N. Mattern, b H. Wendrock, b U. Kuehn, b A. Gebert, b J. Eckert, b A.L. Greer, c J. Sort d and M.D. Baro ´ a a Departament de Fı ´sica, Facultat de Cie `ncies, Universitat Auto ` noma Barcelona, 08193 Bellaterra, Spain b Leibniz Institute for Solid State and Materials Research IFW Dresden, P.O. Box 27 00 16, D-01171 Dresden, Germany c Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, UK d ICREA and Departament de Fı ´sica, Facultat de Cie `ncies, Universitat Auto ` noma Barcelona, 08193 Bellaterra, Spain Received 25 August 2006; revised 26 September 2006; accepted 26 September 2006 Available online 19 October 2006 The deformation behavior of rapidly solidified two-phase amorphous Ni–Nb–Y alloy has been investigated by nanoindentation and high-resolution scanning electron microscopy and correlated with the mechanical properties of the two individual phases composing the system (Ni–Y and Ni–Nb). While the elastic deformation of the two-phase alloy obeys the rule of mixtures for a composite, the plastic deformation is governed by the softer matrix but enhanced, in part, by the deflection of shear bands by the globular harder phase. Ó 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Rapid solidification; Nanoindentation; Metallic glasses; Phase separation Metallic glasses show unusual deformation behavior due to their amorphous structure, which confers on them unique mechanical properties [1]. The absence of defects that control the mechanical behavior of crystalline alloys allows metallic glasses to exhibit a remarkably high elas- tic deformation, that is, a high ratio of strength to elastic modulus [2]. Furthermore, the deformation behavior of these materials at low temperatures and high stresses is extremely inhomogeneous and plastic flow is highly localized in thin shear bands [3]. This mechanism of plas- tic deformation in metallic glasses generally results in low ductility in tension and little in compression, limiting their possible structural applications. Different mechanisms have been proposed to over- come the low ductility of metallic glasses, such as precip- itation of a second phase or fine dispersion of porosity [4–6]. Namely, the precipitation of a second phase in the amorphous matrix may disrupt shear-band propaga- tion and hence improve the ductility of these materials at low temperature. Usually, ductile or nanoscale crys- talline phase(s) are used for this purpose [4,5]. However, recent studies have succeeded in obtaining metallic glasses with heterogeneous two-phase amorphous struc- tures [7–12]. A particular case is the Ni–Nb–Y alloy, which is composed of two binary amorphous phases due to the immiscibility gap of the Y–Nb system in the liquid as well as in the solid state, due to the strong positive enthalpy of mixing. It is noteworthy that studies on the mechanical behavior of two-phase metallic glasses are very scarce and the few existing works deal only with systems in which one of the two phases com- posing the metallic glass is nanometric in size [11,12]. The mechanical properties of composite materials are usually understood as being the result of a combination of the individual mechanical properties of each of the constituent phases [13]. The so-called rule of mixtures in isostrain conditions can be expressed as P c ¼ X X i P i ð1Þ where P c is the mechanical property of the composite, and P i and X i are the property and the volume fraction of the ith composing phase, respectively. Recently, several authors have investigated the mech- anisms of deformation in metallic glasses by means of nanoindentation tests [14–17], a technique that has proven to be very useful in the study of the mechanical properties and deformation behavior of solid materials, 1359-6462/$ - see front matter Ó 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.scriptamat.2006.09.026 * Corresponding author. Tel.: +34 935811401; fax: +34 935812155; e-mail: amadeu.concustell@uab.es Scripta Materialia 56 (2007) 85–88 www.actamat-journals.com