Surface tension-driven shape-recovery of micro/nanometer-scale surface features in a Pt(57.5)Ni(5.3)Cu(14.7)P(22.5) metallic glass in the supercooled liquid region: A numerical modeling capability

Abstract

Recent experiments in the literature show that micro/nano-scale features imprinted in a Pt-based metallic glass, Pt57.5Ni5.3Cu14.7P22.5 [Pt subscript 57.5 Ni subscript 5.3 Cu subscript 14.7 P subscript 22.5], using thermoplastic forming at a temperature above its glass transition temperature, may be erased by subsequent annealing at a slightly higher temperature in the supercooled liquid region (Kumar and Schroers, 2008). The mechanism of shape-recovery is believed to be surface tension-driven viscous flow of the metallic glass. We have developed an elastic–viscoplastic constitutive theory for metallic glasses in the supercooled liquid temperature range at low strain rates, and we have used existing experimental data in the literature for Pt57.5Ni5.3Cu14.7P22.5 [Pt subscript 57.5 Ni subscript 5.3 Cu subscript 14.7 P subscript 22.5] (Harmon et al., 2007) to estimate the material parameters appearing in our constitutive equations. We have implemented our constitutive model for the bulk response of the glass in a finite element program, and we have also developed a numerical scheme for calculating surface curvatures and incorporating surface tension effects in finite element simulations. By carrying out full three-dimensional finite-element simulations of the shape-recovery experiments of Kumar and Schroers (2008), and using the independently determined material parameters for the bulk glass, we estimate the surface tension of Pt57.5Ni5.3Cu14.7P22.5 [Pt subscript 57.5 Ni subscript 5.3 Cu subscript 14.7 P subscript 22.5] at the temperature at which the shape-recovery experiments were conducted. Finally, with the material parameters for the underlying elastic–viscoplastic bulk response as well as a value for the surface tension of the Pt-based metallic glass fixed, we validate our simulation capability by comparing predictions from our numerical simulations of shape-recovery experiments of Berkovich nanoindents, against corresponding recent experimental results of Packard et al. (2009) who reported shape-recovery data of nanoindents on the same Pt-based metallic glass.