Microstructure and fracture strength of different grades of freestanding diamond films deposited by a DC Arc Plasma Jet process

The mechanical properties of chemically vapor deposited diamond films can be characterized in terms of fracture strength. In this paper, different grades of freestanding diamond films were deposited by DC Arc Plasma Jet chemical vapor deposition (CVD) under a variety of deposition conditions. The microstructure and fracture strength of different grades of diamond films were investigated by SEM, X-ray diffraction, Raman spectroscopy and three-point bending, respectively. The columnar structure has great influence on fracture strength; if a columnar structure exists in diamond films, we have found that the fracture strength may not higher than 250 MPa. There is a trend that dominant orientations of optical and mechanical grade diamond films with higher fracture strength are all {220}. As for the fracture mode, optical grade diamond film is mainly intergranular fracture at the lower temperature; at the higher deposition temperature, optical grade diamond film show transcrystalline fracture mode. Fracture mode of mechanical grade diamond film is mainly transcrystalline fracture.