Ball Burnishing Induced Shear Band Proliferation in Zr-Based Bulk Metallic Glass: Experiments and Numerical Prediction

This study attempts to elucidate the effects of ball burnishing (BB) on the mechanical performance of Zr65Ni10Cu15Al10 bulk metallic glass, particularly shear band (SB) proliferation. Both experimental and numerical evaluations of residual stresses (RSs) following the BB cold mechanical treatment are presented. Taguchi's design method was used to determine the optimal values for three important parameters: the burnishing force, the penetration depth and the burnishing feed rate. The results showed that the optimal combination of BB parameters is close to 500 N, 0.20 mm and 60 mm/min. Scanning electron microscopy and atomic force frictional characterization indicated that burnishing processing promotes hardened zones because of the multiplication and interaction of SBs in the subsurface region. Moreover, nanoindentation tests of burnished samples revealed an increase in elastic recovery (hr/hm) of around 14 %, reduced modulus (Er), ratio of plastic work (Wp) to total indentation work (Wt) and hardening. A 3D finite element simulation coupled with user material subroutine including Spaepen's micromechanical model was developed. The constrained deformation of the material around the ball showed incomplete circular patterns of SBs seen in spherical caps whose location, shape and size were captured well by the numerical simulations. The analysis was also able to predict the evolution of RS field profiles in SB intersection sites.