SIMULATIONS OF NANOINDENTATION IN A NON-CRYSTALLINE METAL FILM

A series of molecular dynamics simulations of nanoindentation in a two-dimensional model of a thin metallic glass film exhibit varying degrees of shear localization below the indenter depending on the means of glass processing. The indenter is circular, and all tests were performed at 9.2 % of the glass transition temperature (Tg). The glasses were created from a melt 7.7 % above Tg by: (I) quenching gradually over a period of approximately 0.5 µs, (II) quenching quickly over a period of approximately 10 ns, and (III) quenching instantaneously from a well-equilibrated liquid state. Indentation was performed at approximately 0.3 m/s to a depth of 8nm. During nanoindentation shear bands nucleated at an indentation depth of approximately 15 Å in the gradually quenched samples. In the shear band region material that previously exhibited local quasi-crystal-like structural ordering transformed into purely amorphous material under deformation. This structural transition appears to be related to the softening mechanism that results in strain localization in the material. Substantially less localization occurred in samples produced by higher rates of quenching.