JOURNAL OF MATERIALS SCIENCE 40 (2 0 0 5 ) 1937 – 1941 Shear band formation and mechanical properties of cold-rolled bulk metallic glass and metallic glass matrix composite J. S. PARK, H. K. LIM, J.-H. KIM, J. M. PARK Center for Noncrystalline Materials, Department of Metallurgical Engineering, Yonsei University, Seoul 120-749, Korea W. T. KIM Division of Applied Physics, Cheongju University, Cheongju 360-764, Korea D. H. KIM ∗ Center for Noncrystalline Materials, Department of Metallurgical Engineering, Yonsei University, Seoul 120-749, Korea E-mail: dohkim@yonsei.ac.kr The effects of cold rolling on the mechanical properties of monolithic Vitreloy 1 (Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 Be 22.5 ) BMG and ductile phase reinforced in-situ composite (Zr 56.3 Ti 13.8 Cu 6.9 Ni 5.6 Nb 5.0 Be 12.5 ) have been investigated. The bend strength of the as-cast composite was lower than that of the as-cast monolithic BMG. However, the bend deflection of the as-cast composite (∼1.0 mm) was significantly higher than that of the as-cast monolithic BMG. The ductility of the monolithic BMGs is improved by cold rolling. In contrast, the ductility of the metallic glass matrix composite is deteriorated after cold rolling. C  2005 Springer Science + Business Media, Inc. 1. Introduction The fabrication of large size bulk metallic glasses (BMGs) has accelerated the development of various BMG systems [1, 2]. However, due to the brittle na- ture of monolithic BMGs upon applied loading, a widespread application for structural use has been lim- ited [2]. In order to control the mechanical behav- ior of BMGs, the fabrication of in-situ ductile phase reinforced BMG matrix composite system has been attempted in several systems and exhibited a signif- icant enhancement of toughness due to the incorpo- rated secondary phases [3–5]. Among the BMGs and composite systems, the monolithic Vitreloy 1 (Vit. 1, Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 Be 22.5 ) and ductile β phase rein- forced BMG matrix composite (Zr 56.3 Ti 13.8 Cu 6.9 Ni 5.6 - Nb 5.0 Be 12.5 ) are attractive systems due to a slow cool- ing rate required for large size BMG formation and con- trollable mechanical properties by incorporated ductile phase [3]. The mechanical behavior of monolithic Vit. 1 and the composite have been studied intensively [3]. It has been reported that the ductile β phase in the compos- ite deflects shear band propagation and promotes the creation of multiple shear band formation, resulting an improvement of ductility, while the monolithic Vit.1 showed a brittle nature upon mechanical tests [3]. In general, it has been understood that formation of a large ∗ Author to whom all correspondence should be addressed. number of shear bands is crucial in enhancing the duc- tility of BMG and/or BMG-based composite systems. When BMG-based composite exhibits large elongation, a large number of shear bands usually have been ob- served at the surface of the specimen after compression tests [6]. At the same time, since the pre-introduced shear band itself can possibly serve as nucleation site for shear band formation, attempts have been made to improve the ductility of BMGs by conventional cold rolling [7]. It has been reported that during cold rolling process of Zr-based monolithic BMG, a large density of pre- introduced multiple shear bands has been generated and thus the ductility is increased due to pre-introduced shear bands, indicating that the increased amount of pre-introduced multiple shear bands provides an op- portunity for relatively homogeneous strain relaxation of BMGs [7]. However, a comparative study for BMG and BMG-based composite upon equivalent applied de- formation has not been investigated yet, even though a distinct microstructural evolution of BMG and BMG- composite upon cold rolling can provide a useful insight for controlling mechanical properties and for investigat- ing deformation characteristics associated with shear band formation. In the present study, we selected monolithic Vit. 1 and β phase reinforced BMG matrix composite. Since 0022–2461 C  2005 Springer Science + Business Media, Inc. 1937