Revealing the size-dependent plastic flow transition in nanoscratching an atomically flat Pt-based bulk metallic glass via nonlinear dynamics

Although tip-size-dependent plastic-flow transitions have been widely observed during nanoscratching, the dynamic mechanism underlying lateral force fluctuations remains unclear. In this work, nanoscratching of Pt-based bulk metallic glass was performed using tips with radii from 5 to 30 nm, and nonlinear dynamics was employed to analyze the statistical organization of plastic events. The lateral force evolves from high-frequency, low-amplitude fluctuations at 5 nm to low-frequency, high-amplitude serrations at 30 nm. Meanwhile, the critical slip fluctuation size increases from 13.99 to 97.77, indicating an enlarged characteristic scale of burst-like plastic release. The largest Lyapunov exponent changes from −2.8 × 10−3 to 3.0 × 10−3, while the Hurst exponent decreases from 0.69 to 0.52, revealing reduced dynamic stability and weakened long-range correlation. These results indicate a transition from a self-organized critical state to a chaotic state. Overall, increasing tip radius promotes prolonged stress accumulation and localized rapid release, driving plastic deformation from homogeneous and dispersed flow toward localized burst-like flow under nanoscale contact.