Indentation Behavior of Zr-Based Metallic-Glass Films via Molecular-Dynamics Simulations
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METALLIC glasses exhibit moderate stiffness and high hardness suitable for a variety of engineering applications.[1,2] Both experimental and computer-simulation studies have been conducted extensively to obtain a better understanding of the mechanical behavior of metallic glasses. For example, the nanoindentation experimental results[3] and the temperature dependence of hardness and modulus of metallic glasses[4] provide researchers the experimentally measured hardness and modulus for the validation of simulation results. General indentation considerations can be found in Reference 5. Other experimental measurables, such as the pileup index,[6] can be used to verify simulations. In the current study, the Zr-based (Zr47Cu31Al13Ni9, in atomic percent) metallic-glass thin YUN-CHE WANG, Assistant Professor, and CHUN-YI WU, Ph.D. Student, are with the Materials Program, Department of Civil Engineering, National Cheng Kung University, Tainan 70101, Taiwan R.O.C. Contact e-mail: [email protected] JINN P. CHU, Professor, is with the Department of Polymer Engineering and Graduate Institute of Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan R.O.C. PETER K. LIAW, Professor, is with the Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996. Manuscript submitted April 1, 2009. Article published online July 7, 2010 3010—VOLUME 41A, NOVEMBER 2010
films manufactured via the annealing-induced glass transformation[7–9] is adopted as a model material to study its indentation behavior by molecular dynamics (MD) simulations. The annealing-induced amorphization in the Zr-based metallic glass is different from the solid-state diffusion reaction, also known as the solid-state amorphization (SSA) process, in that the SSA cannot provide a complete amorphization unless very thin multilayered films are used.[10,11] Similar studies have been performed in the Au-La system to study SSA, and it was found that a large negative heat of formation and a large atomicsize difference between the constituents are necessary.[12] The annealing-induced amorphization is that the amorphous phase forms as an intermediate phase during annealing before the thermodynamically stable crystalline phases form at temperatures greater than the glass transformation temperature (Tg) of the metallic glass. The annealing-induced amorphization can be considered a special case of SSA.[7] MD simulations have become a general tool in studying the deformation mechanisms in materials.[13] For example, the medium-range order of the metallic glass has been discussed in Reference 14 with MD simulations. Strain localizations under the indentation for a two-dimensional, Lennard-Jones system are studied with MD.[15] A theory on shear bands, extending the shear transformation zone (STZ) theory, has been METALLURGICAL AND MATERIALS TRANSACTIONS A
proposed recently based on MD simulation results.[16] The connections between volume changes and shear softening in amorphous metals through MD calculation
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