Materials Science and Engineering A 399 (2005) 128–133 Compressive behavior of wire reinforced bulk metallic glass matrix composites Seung-Yub Lee a , Bjørn Clausen b , Ersan ¨ Ust¨ undag d,∗ , Haein Choi-Yim a , C. Can Aydiner d , Mark A.M. Bourke c a Department of Materials Science, M/C 138-78, California Institute of Technology, Pasadena, CA 91125, USA b Lujan Neutron Science Center, Los Alamos National Laboratory, Los Alamos, NM 87545, USA c Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA d Department of Materials Science and Engineering, Iowa State University, Ames, IA 50011, USA Abstract Bulk metallic glasses (BMGs) possess a unique set of mechanical properties that make them attractive structural materials. However, when loaded without constraint, BMGs fracture catastrophically due to formation of macroscopic shear bands and this behavior reduces their reliability. To address this issue, BMG matrix composites have been developed. In this investigation, neutron diffraction was used during uniaxial compressive loading to measure the internal strains in the second phases of various BMG composites reinforced with Ta, Mo, or stainless steel wires. The diffraction data were then employed to develop a finite element model that deduced the in situ constitutive behavior of each phase. It was found that the reinforcements yielded first and started transferring load to the matrix, which remained elastic during the whole experiment. While the present composites exhibited enhanced ductility, largely due to their ductile reinforcements, they yielded at applied stresses lower than those found in W reinforced composites. © 2005 Elsevier B.V. All rights reserved. Keywords: Bulk metallic glass; Composite; Neutron diffraction; Finite element modeling; Uniaxial compression 1. Introduction Bulk metallic glasses (BMGs) are attractive structural materials due to their unique mechanical properties: large elastic strain limit (about 2%), high strength (above 2 GPa), good fracture toughness (about 20 MPa m 1/2 ), good specific strength, high corrosion resistance and so on [1–3]. However, they exhibit poor ductility at room temperature as they usually fail catastrophically under unconstrained loading due to un- stable shear band formation. Several BMG composites have been produced to mitigate this failure mode [4–7]. Among different kinds of composites developed, those with continu- ous unidirectional metallic wire reinforcements have exhib- ited enhanced mechanical properties. For instance, compos- ites with Vitreloy 1 (Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 ) matrix and 20–80 vol.% W wires have nearly preserved the high ∗ Corresponding author. Tel.: +1 515 294 9678; fax: +1 515 294 7202. E-mail address: ustundag@iastate.edu (E. ¨ Ust¨ undag). yield strength of the BMG but have added significant ductility (total strain to fracture reaching 15–20% in compression) [5]. Our recent work using neutron diffraction (ND) and fi- nite element modeling (FEM) has elucidated the bulk de- formation mechanisms in the W wire composites [8,9]. We showed that significant thermal residual stresses develop in these composites due to the coefficient of thermal expan- sion (CTE) mismatch between the matrix and reinforce- ments [8]. Specifically, these stresses are generated dur- ing cooldown starting around the glass transition temper- ature of the matrix and can exceed -500 MPa in the ax- ial direction of the W wires [8]. When the W compos- ites are loaded in compression, these compressive thermal residual stresses induce yielding in the W wires at applied stresses lower than those expected in a residual-stress-free composite [9]. This investigation also showed that it is al- ways the W wires that first experience plastic deformation followed by “yielding” in the BMG matrix in the form of multiple shear band formation [9]. The presence of the W wires stabilizes the production of multiple shear bands in the 0921-5093/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2005.02.032