Fracture behavior of thick diamond films prepared by DC are plasma jet method

The ball-on-ring method was used to investigate the fracture behavior of thick diamond film samples prepared by high-power DC plasma jet CVD method. Both as-grown and polished samples were tested. Great efforts were made to correlate the data obtained to the microstructural features of the tested samples, particularly to the grain size and the pre-existing defects. For as-grown samples, the data were widely scattered such that it was hard to find any grain size dependence on fracture strength and toughness. Whilst for polished samples, a linear relationship of fracture strength to the inverse of the square root of the grain size (the well-known Fetch-Hall equation) was found to fit the data reasonably well. This suggests that grain refinement is also an effective way for improving the mechanical properties of CVD diamond films. Pre-existing micro-cracks are also an important factor affecting the mechanical properties of thick CVD diamond films. (C) 1998 Elsevier Science S.A.