Fracture of synthetic diamond

Abstract

The fracture behavior of synthetic diamond has been investigated using indentation methods and by the tensile testing of pre‐notched fracture‐mechanics type samples. Specifically, the fracture toughness of free‐standing diamond plates, grown by chemically‐vapor deposited (CVD) methods, was measured using Vickers indentations and by the use of disk‐shaped compact‐tension specimens; the latter method provides an evaluation of the through‐thickness fracture properties, whereas the indentation method was performed on the nucleation surface of the sample. Measured fracture toughness (K_c) values were found to be approximately 5–6 MPa√m by both methods, indicating that the fracture resistance of CVD diamond does not vary appreciably with grain size (within the certainty of the testing procedures). Complications, however, arose with the fracture‐mechanics testing regarding crack initiation from a relatively blunt notch; further work is needed to develop pre‐cracking methods to permit more reliable fracture toughness testing of diamond.