Atomic Force Microscopy as a Means to Analyze Vickers Indentation Experiments: Crack Morphology, Fracture Toughness, and Indentation Profile

Studies of micro/nanoscale mechanical properties of materials are scarce and the determination of the corresponding parameters such as fracture toughness (KIC) and Vickers hardness number (HV) at those scales remains a challenge. In the presented work, a methodological approach was applied that provides detailed insight on the elastic/plastic behavior of minerals subjected to Vickers indentation experiments. In this research, five samples were analyzed: one fused silica sample (reference material), two synthetic quartz crystals (differently cut, SQ⊥ and SQX), and two quartz grains from polished sections of granite and granodiorite rock. The applied methodology was predominantly based on qualitative and quantitative morphology measurements by Atomic Force Microscopy (AFM). This analysis shows the dominant presence of either Primary Radial Cracks (PRC) or Secondary Radial Cracks (SRC) in both natural (mineral) quartz grains and synthetic quartz crystals, and Cone Cracks (CC) in fused silica. Moreover, the parameters associated with the indentation (e.g., length of the cracks, the depth of residual indentation, and the indentation mark size) allowed the reconstruction of the indentation profile model and the determination of KIC and HV with enhanced accuracy.