Experimental Studies and Molecular Dynamics Simulations of the Sliding Contact of Metallic Glass
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Experimental Studies and Molecular Dynamics Simulations of the Sliding Contact of Metallic Glass Xi-Yong Fu1, Michael L. Falk2 and David A. Rigney1 1 Materials Science and Engineering, The Ohio State University, Columbus, 43210 OH U.S.A. 2 Materials Science and Engineering, University of Michigan, Ann Arbor, 48109 MI U.S.A. ABSTRACT Tribological properties of bulk metallic glass Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 were studied experimentally using a pin/disk geometry without lubrication. Experimental observations were compared with 2D molecular dynamics simulations of amorphous material in sliding contact. The friction coefficient and the wear rate of bulk metallic glass (BMG) depend on normal load and test environment. The sliding of annealed BMG re-amorphizes devitrified material. A mechanically mixed layer is generated during sliding; this layer has enhanced oxygen content if the sliding is in air. The MD simulations show that atomic scale mixing occurs across the sliding interface. The growth kinetics of the mixing process scales with the square root of time. In the simulations, a low density region is generated near the sliding interface; it corresponds spatially to the softer layer detected in experiments. Subsurface displacement profiles produced by sliding and by simulation are very similar and are consistent with the flow patterns expected from a simple Navier-Stokes analysis when the stress state involves both compression and shear. INTRODUCTION The development of bulk metallic glass (BMG) has renewed interest in research on glassy metals. The amorphous structures of BMG lead to new combinations of properties for various engineering applications [1, 2]. However, very little is known about the tribological properties of these novel materials. In this work, the friction and wear properties of bulk metallic glass have been studied. In addition to experimental investigations, a complementary molecular dynamics (MD) simulation was conducted. The combined results from the experiments and simulations provide useful insights into the behavior of metallic glass materials under sliding conditions. EXPERIMENTAL INVESTIGATIONS
strain gauges
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Material and Experimental Setup W Friction and wear properties of bulk metallic glass alloy load Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 (Vitreloy, composition in at. %) provided by Howmet Corp. were investigated using a pin/disk pin geometry without lubrication. Fig.1 illustrates the setup of the test disk apparatus. The pumping system allows experiments to be carried out either in ambient air or in vacuum (typically 4.0×10-3 Pa). The disks were 31mm in diameter and 3mm in thickness. Pins were pumping either BMG rods (3mm×3mm×12mm) or 52100 bearing steel system balls with 6 mm diameter. Friction force was monitored by a full bridge arrangement of four strain gauges mounted on the pin Fig.1 Experimental setup holder arm. Worn surfaces and debris were characterized by XRD (Scintag PAD-V with Cu Kα), SEM/EDS (Philips XL-FEG), TEM (Philips CM200 and CM-300 FEG) and microhardness. The s
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