ATOMIC-FORCE MICROSCOPY OBSERVATIONS OF IRON-SAPPHIRE FRACTURE SURFACES

Planar iron-sapphire interfaces were fractured along the interface and the iron side examined with an atomic force microscope in an ambient environment. Al2O3 pegs, which span the interface and which fracture i n a brittle manner near the interface, were observed on the Fe surface . These pegs are less than 0.5 mu m in diameter, with an average spaci ng of a few micrometers. Striations, produced by plasticity at the cra ck front, are also observed with an amplitude of a few nanometers. Var iations in the spacing and height of these striations indicate that th ese brittle pegs do toughen the interface, even though the failure of the pegs themselves appears to be purely brittle, involving no energy- dissipative process.