CVD diamond coating of forming dies with a homogenous coating thickness

Abstract

Ball-on-plate tribometer tests have already shown that polished polycrystalline CVD diamond coatings in dry tribological contact with aluminium lead to low wear rates and a low coefficient of friction of 0.12. The possibility to coat the forming zone of forming dies was investigated in this study to evaluate the applicability of CVD diamond coatings for a tapering process of aluminium rods. The results are examined by laser-scanning confocal microscopy, scanning electron microscopy and cryofractures. CTF12D carbide grade dies with a height of 5 mm and an inner diameter of 7.8 mm could be coated with a laser-based plasma CVD process with a CVD diamond coating with a homogeneous thickness of 2.3 microm. The standard deviation of the coating thickness variation is only 0.1 microm in the entire forming zone. This was achieved by combining an etching process, a masked diamond nucleation, a specially fabricated rotating substrate holder and turning the die upside down after half the coating time so that the plasma flame enters through the other opening of the die.