Strong configurational dependence of elastic properties for a binary model metallic glass

Abstract

In this work, the strong dependence of elastic properties on configurational changes in a Cu-Zr binary metallic glass assessed by molecular dynamics simulations is reported. By directly evaluating the temperature dependence and configurational potential energy dependence of elastic constants, the shear modulus dependence on the specific configurational inherent state of metallic glasses is shown to be much stronger than the dependence on Debye-Grüneisen thermal expansion. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2360203͔ Bulk metallic glasses ͑BMGs͒ have acquired considerable attention from scientific and technological view points in the last two decades. 1-9 BMGs have very high yield strength, at least double that of ordinary commercially used crystalline materials, and high elastic strain limit, roughly 2% in tension or compression due to their disordered atomic structure. [1][2][3][4] Upon yielding BMGs tend to form highly localized shear bands, where one observes large local plastic strains. [10][11][12] To describe the yielding in metallic glasses a cooperative shear model 13 has been developed for the glassy state based on potential energy landscape ͑PEL͒/inherent state ͑IS͒ theory. 14-16 A scaling relationship among the shear flow barrier, a universal critical yield strain, and the isoconfigurational shear modulus G was constructed. The model reveals that for a fixed glass configuration the barrier height for shear flow is proportional to the isoconfigurational shear modulus G, which makes the elastic properties of great importance to fully understand the mechanical behaviors of BMGs. A wide variety of experimental work has been performed to measure the elastic properties of BMGs. 4,17,18 Molecular dynamics ͑MD͒ simulations have been extensively utilized to calculate the elastic stiffness coefficients in crystals. 19,20 In this work we present the Debye-Grüneisen thermal expansion effect as well as the strong configurational inherent state dependence of the elastic properties for a model binary metallic glass.In order to obtain numerical results for the elastic stiffness coefficients, we perform MD simulations using an interatomic many-body Rosato-Guillope-Legrand-type potential model developed for Cu-Zr binary alloy system. 21 The original simulation cell contains N = 2000 atoms, arranged in a random bcc structure with periodic boundary conditions. At the beginning, the system was heated to 2400 K and the structure of the liquid phase was allowed to equilibrate. The system was then cooled to 50 K under zero pressure using a range of quenching rates from 1 to 10 K / ps ͑1 ps=10 −12 s͒ to generate glass configurations. This yielded the reference shapes and size matrices, h 0 , in Parrinello-Rahman formalism 22 to calculate elastic stiffness coefficients by constant temperature and constant volume ͑nvt͒ simulations. The glass transition temperature occurs at 700 K under the cooling rate of 5 K / ps, and there is a slight difference among the glass transition temperatures when varying the coolin...

Deformation behavior of an amorphous Cu64.5Zr35.5 alloy: A combined computer simulation and experimental study

“…29 Also, the quench rate in Ref. 24 was approximately ten times higher than in our work, which could also have an effect due to configurational relaxation differences. It is interesting to note that for our Cu 64.5 Zr 35.5 metallic glass, the calculated Poisson's ratio for the supercooled liquid is a little higher than 0.5 and the shear modulus is slightly negative.…”

“…Using this approach, we find that the temperature dependences of the Poisson's ratio and shear modulus ͑Fig. 3͒ clearly display a transition between the amorphous solid to the supercooled liquid at T ϳ 1000 K. Note that Duan et al 24 performed MD simulations on a metallic glass richer in Zr, Zr 54 Cu 46 and found comparable decreases in bulk and shear moduli with increasing temperatures below T g . Between 300 and 500 K, the values of these two elastic constants are considerably higher in the Cu 64.5 Zr 35.5 alloy examined in our study.…”

“…For instance, MD simulations of Cu-Zr glasses were performed to investigate the influences of temperature and configurational potential energy on elastic properties. 24 Similarly, MD simulations with simple pair potentials were utilized to examine the effects of alloy composition on the different degrees of free volume, as determined using Voronoi polyhedra analyses. 25 We have recently developed a FS potential for the Cu-Zr system.…”

Anelastic to Plastic Transition in Metallic Glass-Forming Liquids

“…More precisely, G was found to be a unique decreasing function of h independent of whether h is induced by thermal excitation or mechanical deformation [11,15]. This decreasing dependence of G on h reflects the decreasing curvature of the potential energy density function with increasing configurational energy and has been validated computationally [17]. In the inset in Fig.…”

Study on crystallization kinetics of binary alloys through model colloidal mixtures

“…This compositional complexity makes it extremely difficult for different atoms to rearrange their spatial positions so that they are frozen directly into a disordered glassy structure upon cooling. Recently, binary BMG forming alloys have also been developed in a few alloy families [6][7][8][9][10][11][12][13][14], and their GFA is found to be very sensitive to the minor change of chemical composition [15,16]. These further confuse the criterions of GFA in metallic alloys.…”