Fracture studies of diamond films on silicon

Diamond coatings were prepared on silicon substrates for fracture studies. Two thicknesses of coatings were evaluated: 6 and 12 μm. The diamond films increased the strength of the silicon for the same size fracture initiating crack and thus caused an apparent toughness increase from 1.2 MPam1/2 for the uncoated silicon to about 1.6 MPam1/2 for the 12 μm coated silicon. Fractography showed that the indentation impression on the coated surface was altered by the coating, but this did not alter the formation of the radial crack beneath the surface so that indentation fracture mechanics can be used for thin coatings with thicknesses below 12 μm. Fractography also showed that the coatings separated from the substrate under and near the indentation site, but was still intact away from the indentation. Most of the fracture in the diamond coating was transgranular indicating good intergranular adhesion.