Cathodic chromium carbide coatings for molding die applications

Chromium carbide coating on steel is a good candidate for applications on forming and molding dies. The high mechanical strength, chemical resistance and high temperature stability of Cr3C2 phase can be compatible with the severe abrasive wear and corrosion found in these manufacture operations. Chromium carbide coatings have been deposited on hardened steel probes by cathodic arc evaporation (CAE) from chromium targets in reactive acetylene gas. The effect of the deposition parameters on the composition and crystalline structure was characterized by means of X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), secondary ion mass spectroscopy (SIMS) and glow discharge optical emission spectroscopy (GDOES). The results show an evolution of the crystalline structure of the coatings from amorphous carbide to Cr7C3 and pure Cr3C2 phase as the C2H2 pressure in the deposition chamber decreases from 6.3 to 0.4 Pa. The adhesion of the Cr3C2 coatings was strongly increased by adding a CrN interlayer. The highest hardness was obtained for the Cr3C2 coatings (22 GPa) while the amorphous carbide showed the lowest hardness (10 GPa) and friction coefficient.