Interaction of nanoscale damages with static and dynamic contact induced damages in alumina: A novel approach using nanoindentation

The present work makes novel usage of the well-known nanoindenation (NI) technique to study how the nanohardness (H) and Young's modulus (E) are affected due to variations in the loading rates ranging from 1 to 1000 mN s(-1) for a pressureless sintered alumina of intermediate e.g., 8 mu m grain size and 91% relative density. The same NI technique is also utilized to understand how the presence of microindentation induced radial cracks affect H and E when the nanoindents are at different angular orientations of 0 degrees, 30 degrees, 45 degrees and 90 degrees with respect to the aforesaid radial cracks. Finally, the study is also extended towards using the NI technique to understand how H and E of the same alumina are influenced by the presence of the dynamic contact induced scratch grooves created at normal loads in the range of 2-15 N. Based on the experimentally measured data, extensive usage of Field Emission Scanning Electron Microscopy (FESEM) and stress magnitude estimations; the nature of the deformation and mode of damage interaction evolution are found to be linked to the nanoscale plasticity events related to localized shear stress developed underneath the nanoindenter, the angular orientations of the nanoindents with respect to the direction of propagation of the radial cracks due to statistically induced contact damage, the magnitude and location of residual tensile stresses developed during scratching as well as the spatial density of micro-cracks underneath the scratch grooves. Finally, the implications of the present results in futuristic development of impact damage resistant alumina ceramic are also discussed