Fracture Toughness and Subcritical Crack Growth in CVD Diamond

Abstract

ABSTRACTThe fracture toughness, stress corrosion and cyclic fatigue properties of polycrystalline chemical vapor deposited (CVD) diamond have been investigated on thick (˜100 to 300 μm) free-standing films. Specifically, the fracture toughness, Kc, of diamond was determined using indentation methods and for the first time by the tensile testing of pre-notched fracture-mechanics type compact-tension samples. Measured Kc values were found to be between 5 and 7 MPa-m1/2 by either method and to be apparently independent of grain size and shape. Studies on subcritical crack growth (i.e., at stress intensities less than Kc) indicated that CVD diamond is essentially immune to stress-corrosion cracking under sustained loads in room air, water and acid environments. Corresponding experiments to examine susceptibility to cyclic fatigue are currently being performed using indentation-precracked cantilever beams cycled in three-point bending.