Simulation and experimental researches on HFCVD diamond film growth on small inner-hole surface of wire-drawing die with no filament through the hole

Based on the traditional deposition technique with the filament through the hole (DTFTH), the growth of high-quality diamond films on inner hole surfaces, especially those with small apertures, is rather difficult and laborious. In the present research, the deposition technique with no filament through the hole (DTNFTH) is proposed, and its feasibility and limitations are discussed on the basis of the radiation computation, temperature simulation, analyses on mean free paths of various active radicals, and the experimental verification of the “shading and distance effects”. It is indicated that the ratio of the hole depth to the hole diameter should be smaller than four. Afterwards, the drawing die with an aperture of 2 mm is designed, and a case study focusing on a single die and the mass production of diamond coated dies by the DTNFTH are both accomplished, using optimized deposition parameters. It is demonstrated that the film thicknesses are in the range of 4.8-6 μm (case study) and 3.5-5 μm (mass production), showing acceptable uniformity. Uncoated, DTFTH- and DTNFTH-diamond coated dies are all submitted to field tests, indicating that the lifetime of the DTFTH-diamond coated die is approximately eight times more than that of the uncoated one, while the DTNFTH-diamond film prolongs the lifetime of the uncoated die by a considerable factor of five.