Nanoindentation of natural diamond

Abstract This study demonstrates that the plane-strain Young's moduli E* = E/(1 - v 2) of natural diamonds with a weight of less than 0.2 carat can be determined by the technique of nanoindentation, where E is Young's modulus and v is Poisson's ratio. The indentation test with a Berkovich indenter was conducted at loads of 50, 100 and 300 mN for three samples; two were ⟨100⟩ oriented and one was ⟨110⟩ oriented. The indentation curves showed almost an elastic behaviour at 50 mN. We evaluated the E* values by analysing the elastic indentation curves with the removal of the contribution of machine compliances due to the machine frame and the deformation of the mount, which was determined from the data obtained during the unloading of the indentation at loads of 100 and 300 mN. The E* values obtained were 1090 and 1217 GPa for ⟨100⟩- and ⟨110⟩-oriented diamonds respectively. These agree reasonably well with the literature values, 1064 and 1169 GPa respectively, measured by an ultrasonic technique. The value for ⟨100⟩-oriented diamond, E* = 1090 GPa, is recommended to use as the value for the diamond indenter, since the indenter is ordinarily manufactured from a natural diamond with its axis along the ⟨100⟩ direction.