INTERFACE MODIFICATION OF SUBSTRATE FOR ENHANCING ADHESIVE STRENGTH OF CVD DIAMOND COATING BY SOLID PARTICLES

Abstract

The strong adhesive strength is essential for the widespread applications of diamond coating in the mechanical field. In this paper, a novel method combining conventional chemical vapor deposition (CVD) diamond technique with solid particles was proposed to modify the interface material properties of substrate to improve the adhesive strength of the diamond coating. Prior to deposition, wet dispersion was adopted to uniformly distribute solid particles on the substrate, with which the diamond coatings with the WC, TiC and BN particles embedded at the interface were fabricated on Co-cemented tungsten carbide (WC-Co) substrate. In addition, the pure diamond coating was also fabricated for comparison. The as-deposited diamond coatings were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDS) and Raman spectroscopy. The results indicated that the diamond coating with TiC exhibited the highest residual stress, which may be due to the larger lattice mismatch between TiC and diamond as compared to WC and BN. The indentation test suggested that WC and BN particles were favorable for the improvement of the adhesive strength and the crack resistance of diamond coating, while this phenomenon was not observed in the diamond coating with TiC particle. This might be caused by the large lattice parameter, high lattice mismatch, and high thermal expansion coefficient mismatch of TiC as compared with diamond. Furthermore, the lattice parameter of additional particles might be an important factor to determine whether or not the adhesive strength of diamond coating can be enhanced, because it determined the compressive stress or tensile stress generated inside diamond coating. Hence, interface modification of substrate by dispersing the solid particles with low lattice parameter or similar material properties of diamond may be an effective and convivence approach to improve the adhesive strength of the diamond coating.