Preparation and Characterization of Ir Coating on WC Ceramic by Double Glow Plasma

Dense and adherent Ir coating was deposited on porous WC ceramic by double glow plasma (DGP). There were two cathodes in the vacuum deposition chamber. The bias voltage of Ir target and WC substrate were −900 and −350 V, respectively. The Ir coating was characterized using scanning electron microscopy, x-ray diffraction, nanoindentation instrument, and scratch tester to examine the microstructure and the mechanical properties. The results indicated that the deposition rate by DGP was up to 5-6 μm/h which was faster than that by metal-organic chemical vapor deposition and magnetron sputtering. The Ir coating had a preferential growth orientation of (220) crystal face. The hardness was 800 HV. The elastic modulus was 644 GPa. The excellent mechanical properties were attributed to the preferential growth, the large compressive stress, and the shrinkage of the lattice parameters. The adhesive force was up to 51 N. The strong adhesion was attributed to the mechanical locking and chemical reaction between the Ir coating and the porous WC substrate.