^aDepartment of Materials Science and Engineering,Pohang University of Science and Technology, Pohang 790-784, Republic of Korea
^bDepartment of Materials Science and Engineering, Korea University, Seoul 136-701, Republic of Korea
^cAdvanced Metals Research Center, Korea Institute of Science and Technology, Seoul 130-650, Republic of Korea

Received 12 May 2009; revised 30 June 2009; accepted 1 July 2009. Available online 4 July 2009.

Abstract

In order to investigate the phase separation behavior in Cu-Zr-Ag bulk metallic glasses (BMGs) on an atomic-level, a modified embedded-atom method (MEAM) interatomic potential for the Cu-Zr-Ag system has been newly developed. A clear tendency of phase separation of Ag-rich phases could be observed in the supercooled liquid, in reasonable agreement with experimental information. The potential can be used for atomistic investigations of the effects of alloying element, Ag, on a wide range of amorphous properties of Cu-Zr BMGs.

Keywords: Cu-Zr-Ag; bulk metallic glasses; MEAM potential; atomistic simulation; phase separation

^aDepartment of Chemical and Materials Engineering, University of Alberta, Canada
^bNational Institute for Nanotechnology, Edmonton, AB, Canada
^cDepartment of Materials Science and Engineering, Rensselaer, Polytechnic Institute, Troy, NJ, USA
^dNational Center for Electron Microscopy, Lawrence Berkeley Lab, Berkeley, CA, USA
^eDepartment of Electrical and Computer Engineering, University of Alberta, Canada

Received 7 October 2008; revised 24 May 2009; accepted 29 May 2009. Available online 29 June 2009.

Abstract

We investigate the bulk and surface features of the crystalline–amorphous transitions in binary Al–Mo alloy thin films as a function of Mo composition using transmission electron microscopy, X-ray diffraction and atomic force microscopy analysis, as well as thermodynamic modeling. Of the alloys tested, the minimum in the root mean square (rms) surface roughness and correlation length occurs at the Al–32 at.% Mo composition, which corresponds to the maximum volume fraction of the amorphous phase and the minimum volume fraction of the body centered cubic nanocrystallites. The rms surface roughness of the 32 at.% Mo films is on the order of a single nanometer, compared with nearly 80 nm for the 50 at.% Mo film. A structure–zone map is constructed to relate the surface morphology of the films to their bulk microstructure. A thermodynamic model developed by Miedema and coworkers was used to predict the general trends observed in the microstructural evolution as a function of film composition.

Keywords: Nanocomposite; Metallic glasses; Nanocrystalline materials; Surface roughness; High-resolution electron microscopy

^aDepartment of Materials Science and Engineering, Pohang University of Science and Technology, Pohang 790-784, South Korea
^bDepartment of Materials Processing, Applied Plasticity Research Group, 531 Changwondaero, Changwon, Gyeongnam 641-831, South Korea
^cIFW Dresden, Institute for Complex Materials, P.O. Box 270116, D-01171 Dresden, Germany
^dInstitute of Materials Science, Dresden University of Technology, D-01062 Dresden, Germany

Abstract

The thermal and mechanical properties of a Zr_66.4Nb_6.4Cu_10.5Ni_8.7Al_8.0 bulk metallic glass composite (BMGC) have been investigated. The thermal properties were determined by using a differential scanning calorimeter (DSC), while the phase and composition analysis of crystalline precipitates within glassy matrix were carried out by X-ray diffraction (XRD). The deformation behavior has also been investigated through a series of compression tests performed under several strain rates between 10⁻⁴ /s and 10⁻² /s at various temperatures within supercooled liquid region (SLR). This BMG composite was found to have improved high temperature strength compared to other Zr-based monolithic BMGs. The in-situ formed crystalline phases are believed to hinder the viscous flow of glassy matrix to raise the high temperature strength, compensating more the minor softening of crystalline phases at higher temperatures within the SLR. The warm formability of the composite was also estimated by applying the dynamic materials model (DMM) and the results were verified by subsequent laboratory-scale extrusion tests.

Keywords: Bulk metallic glass composite; Supercooled liquid region; Warm Formability; Extrusion

^aDepartment of Metallurgical Engineering, Banaras Hindu University, Varanasi 221005, India
^bNational Metallurgical Laboratory, Jamshedpur 831007, India
^cInstitut fuer Werkstofftechnik, Universitaet Bremen, Badgasteiner Str. 3, 28359 Bremen, Germany