The deformation behaviour of crossed diamond wedges in the scanning electron microscope

Experiments have been carried out in which two sharp diamond wedges were pressed together orthogonally under a known load inside a scanning electron microscope. The object of the experiment was to ascertain whether plastic deformation is possible in diamond at room temperature when it is subjected to shear stresses approaching the theoretical strength of a perfect diamond crystal. Calculation shows that it should be possible to achieve shear stresses of this magnitude using a crossed-wedge geometry in which the stresses are predominantly compressive. The wedges were made from type IIb diamond by cleavage. The results showed that there was a threshold load below which no damage of any sort could be detected on the edges of the diamonds. Above this value, indentation occurred suddenly. Subsequent examination of the indentation showed it to have a very jagged appearance as if it had been formed by a fracture process. It was concluded that plastic deformation is not possible in diamond at room temperature except possibly in very small amounts not resolvable in the scanning electron microscope.