Investigation on Work Hardening Behavior of Bulk Metallic Glass under Nanoscale Wear

Based on an atomically flat Pt-based bulk metallic glass (Pt-BMG) processed by thermoplastic imprinting, the work hardening behavior of Pt-BMG under nanoscale wear is investigated by atomic force microscopy (AFM). It is found that the wear of Pt-BMG subjected to different number of cycles exhibited two distinct stages, and the wear rate at low load range (57 nN～108 nN) is significantly higher than that of the high load range (216～324 nN). This is because the wear under low loads is dominated by the surface oxide film, while the wear under high loads is controlled by the Pt-BMG matrix. With increasing the number of cycles from 1 to 10, the wear rate of Pt-BMG demonstrates a gradual decreasing trend, and the decreasing trend became more and more pronounced with the increase in cycle number. Specially, the wear rate of Pt-BMG is almost unchanged when the number of cycles is increased from 5 to 10; By decoupling the contribution of adhesive friction and plowing friction in wear with JKR model, the shear strength to displace the material ahead of the tip increases significantly from 3.32 GPa to 5.20 GPa with increasing the number of cycles from 1 to 5. Further increasing the cycle number to 10, the shear strength increases slightly to 5.41 GPa. This coincides with the trend of the wear rate versus the number of cycles, and thus verifies the existence of the work hardening effect of Pt-BMG occurred in nanoscale wear; The work hardening behavior observed in nanoscale wear of Pt-BMG is strongly dependent on the stress state and deformation scale, and the confined stress state under the nanoscale scratch condition promotes the atomic diffusive relaxation ability within the stressed volume in structure and inhibits the shear localization. As a result, the annihilation rate of free volume induced by structural relaxation is faster than that of free volume generation rate induced by shear dilation, therefore leading to the structural densification and the resultant work hardening effect. © 2025 Chinese Mechanical Engineering Society. All rights reserved.