Damage evolution in spark plasma sintered boron carbide under scratch and indentation loading conditions

Spark plasma sintered boron carbide (B4C) has been tested for damage evolution characteristics. Three distinct failure regions were identified during the scratch process of B4C, based on the observed transitions in the induced tangential force pattern and fracturing. B4C exhibited significant elastic recovery effect (50%) under both scratch (1-50 N) and indentations (5-100 mN) loading conditions. The sequence of transition from the nucleation of cracking and its propagation resulting to amorphization were identified. Scratch grooves were characterized with partial bow type Hertzian cracking, radial cracking and an onset of chipping (up to 75 N) and extensive spallation and fragmentation (76-100 N). The spallation regions were characterized with numerous randomly oriented slip lines suggesting failure dominated by the shear deformation. Raman spectra from spallation regions reveal peaks corresponding to amorphous B4C, inferring the occurrence of amorphization concentrated at the localized shear bands. At higher loads (>75 N), grain boundary fractures were observed in addition to simple cleavage fracture, which contributes for deteriorating material performance, by extensive cracking. The hardness and elastic modulus of B4C measured by nanoindentation were 44 GPa +/- 6.6 GPa and 560 GPa +/- 47 GPa, respectively.