Effect of DC bias and RF self-bias on the structure and properties of chromium oxide coatings prepared by vacuum cathodic arc deposition

Cr ₂ O ₃ coatings were prepared by vacuum cathodic arc deposition (VCAD) on cemented carbide YT15 at different voltages of both direct current (DC) and radio frequency (RF) bias. The structure and properties of the coatings were investigated by scanning electron microscope, X-ray diffraction, and nanoindentation. With both DC and RF bias, coatings deposited at zero and low bias voltage exhibit a columnar structure and a preferred orientation (PO) of (104). As the bias voltage increases, the columnar structure starts to disappear and PO gradually becomes (006). Besides, the crystallite size of the coatings declines as the bias voltage increases. Comparing to DC bias, the RF bias leads to smaller crystallite size by virtue of higher energy and density of ion bombardment. The electrical resistivity of the coatings and saturation ion current density during deposition were measured to explain this effect. The hardness of the coatings was significantly enhanced by the bias voltage, particularly by the RF bias. A nano-hardness of 44.7 GPa was found in the coating deposited under −100 V RF bias, which has not been previously reported.