Indentation-induced subsurface damage in silicon particles of Al-Si alloys

Damage microstructures generated beneath the Vickers indentation applied to the silicon particles in an Al-18.5 wt.%Si alloys were studied. Plastic deformation at low loads and volume expansion due to subsurface crack formation at high loads (>650 mN) were responsible for pile-up formations around the indentations. The probability of lateral cracks reaching the surface and causing particle fracture was shown to obey Weibull statistics with a low modulus. The indentation pressure estimated as 19.3 GPa induced the transformation of diamond cubic Si-I to bcc Si-III and rhombohedral Si-XII, as observed by Raman microspectroscopy. Cross-sectional FIB and TEM revealed a semi-circular plastic core and subsurface lateral crack pattern below the residual indents and a localized amorphous zone at the median crack boundary immediately below the plastic core.