The growth behavior and surface performance enhancement of diamond film deposited on polycrystalline diamond compact

Abstract

Polycrystalline diamond compacts (PDC) are subject to thermal abrasive wear and impact damage when working in harsh downhole environments due to their internal diamond skeleton-cobalt microstructure. Here, the polycrystalline diamond film was deposited on PDC epitaxially by the hot filament chemical vapor deposition technique, which can firmly adhere to the PDC under severe working conditions and enable to enhance its wear resistance. A systematic study is presented into the effects of deposition parameters such as substrate temperature, methane concentration, gas pressure, and hydrogen flow rate on the film growth behavior, including the growth mode and the morphology evolution observed from the edge cross-section and surface by SEM. Under the deposition conditions of high substrate temperature, low methane concentration, low pressure, and large hydrogen flow, the crystal grains show square crystal planes with smooth surfaces and sharp edges, and the film is dominated by epitaxial growth and closely bonded with PDC without cracks and delamination. While under the opposite conditions, with the increase of secondary nucleation and the rapid shrinking of the square crystal plane, the as-grown film and the PDC substrate are loosely bonded with relatively poor adhesion, which is easy to cause edge chipping and peeling off when grinding and not suitable for the surface performance enhancement. After synthesizing the film adhesion, PDC integrity, the quality of crystallization and the film deposition rate, the optimal epitaxial conditions for CVD of PDC were summarized and tested. It was found that after 21 days of decobaltization pretreatment, the diamond films deposited on PDC for 16 h were able to firmly adhere to the substrate and provide the best surface performance enhancement.