Influence of strain rate effect on material removal and deformation mechanism based on ductile nanoscratch tests of Lu₂O₃ single crystal

Nanoscratch tests of Lu₂O₃ single crystal under different scratch velocities were performed using Berkovich and spherical indenters. The experimental results indicated that shallower penetration depth and lager continuous chips were generated during the scratching process when a higher scratch velocity was used. Moreover, two types of plastic flow lines were formed on the crystal surface after testing. A theoretical model on the penetration depth of scratching Lu₂O₃ single crystal was developed by considering the elastic recovery and strain rate effect. The predicted results were found to agree well with the experimental results, and the deviation was within 10%. The transmission electron microscopy (TEM) analysis results of the crack-free subsurface generated during the nanoscratch tests revealed that the ductile removal mechanism dominated by nanocrystalline and amorphous phases. Pressure-induced defects, such as dislocations, stacking faults, and nano twins were observed inside the nanocrystalline phase. High-angle annular dark-field (HAADF) images of the subsurface indicated that a higher scratch velocity could effectively reduce the subsurface damage depth when the normal force was maintained constant.