Ball burnishing effects on mechanical performance of Zr-based metallic glass: modeling and experimentation

The research focuses on the impact of the ball burnishing process on the mechanical properties of Zr65Ni10Cu15Al410 bulk metallic glass. The study combines experimental techniques with finite element modeling to elucidate how this cold mechanical treatment enhances performance through the induction of compressive residual stresses and the multiplication of shear bands. A significant improvement in surface hardness (H) and reduced modulus (Er) was observed in burnished samples compared to the unburnished condition under intensive deformation. Monotonic nanoindentation tests revealed that the burnished samples exhibited superior mechanical behavior, characterized by higher hardness and enhanced elastic recovery. Moreover, increasing the burnishing penetration depth and feed rate led to greater plastic deformation and improved elastic recovery. Scanning Electron Microscopy (SEM) and contact-mode Atomic Force Microscopy (AFM) were employed to analyze subsurface microstructures and surface roughness. The evolution of surface roughness parameters (Ra and Rz) and qualitative frictional properties was determined. An increased number of primary and secondary shear bands was observed in burnished samples compared to the unburnished ones. A three-dimensional finite element model was developed using Abaqus/Implicit. The Drucker–Prager criterion was adopted to describe the material’s plastic flow. The numerical predictions of the residual stress field component (S22) in the feed direction (OY-axis) were found to be consistent with the equi-biaxial residual stresses derived from nanoindentation measurements. The compressive residual stresses reached values on the order of −900 MPa at the contact surface under optimal ball burnishing conditions. It is suggested that the proliferation and interaction of shear bands contribute to the improved ductility observed in burnished samples, demonstrating a direct correlation between microstructural evolution and mechanical performance.