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Laszlo Kecskes U.S. Army Research Laboratory, Weapons and Materials Research Directorate, AMSRD-ARL-WM-MB, Deer Creek Loop, Aberdeen Proving Ground, Maryland 21005-5069

Naresh N. Thadhania) Georgia Institute of Technology, School of Materials Science and Engineering, Atlanta, Georgia 30332 (Received 7 November 2007; accepted 3 January 2008)

The high-strain-rate mechanical properties, deformation mechanisms, and fracture characteristics of a bulk metallic glass (BMG)-matrix composite, consisting of an amorphous Zr57Nb5Cu15.4Ni12.6Al10 (LM106) matrix with crystalline tungsten reinforcement particles, were investigated using gas gun anvil-on-rod impact experiments instrumented with velocity interferometry (VISAR) and high-speed digital photography. The time-resolved elastic-plastic wave propagation response obtained through VISAR and the transient deformation states captured with the camera provided information about dynamic strength and deformation modes of the composite. Comparison of experimental measurements with AUTODYN-simulated transient deformation profiles and free surface velocity traces allowed for validation of the pressure-hardening Drucker–Prager model, which was used to describe the deformation response of the composite. The impacted specimens recovered for post-impact microstructural analysis provided further information about the mechanisms of dynamic deformation and fracture characteristics. The overall results from experiments and modeling revealed a strain to failure of ∼45% along the length and ∼7% in area, and the fracture initiation stress was found to decrease with increasing impact velocity because of the negative strain-rate sensitivity of the BMG.

I. INTRODUCTION

Bulk metallic glasses (BMGs) have become a subject of increasing interest because of their unique properties including superior strength and hardness and excellent corrosion and wear resistance.1 BMGs undergo deformation by shear band initiation and propagation, which causes them to fail catastrophically upon impact. Design of microstructures that inhibit shear band propagation can prevent catastrophic failure and significantly increase the plastic strain to failure.2 Hence, methods to restrict or control shear band propagation need to be developed via addition of an intrinsic or extrinsic crystalline particulate phase. The plasticity and failure properties of BMGs have a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0119 998

J. Mater. Res., Vol. 23, No. 4, Apr 2008

been shown to be improved by nano- or microcrystalline reinforcement particles,3–9 which interfere with the propagating shear bands, causing them to slow and deflect, thus delaying failure and improving the toughness of the material.1,3–5,10–12 By altering the composition, size, morphology, distribution, and amount of the reinforcement particles, there is potential to completely alter the behavior of the metallic glass and therefore to design a material with a tailored deformation response. Tungsten, in pa