Unlubricated friction and wear behaviors of ZrN coatings against hardened steel

Medium-frequency magnetron sputtered PVD ZrN coatings (ZrN, ZrN/Zr) were deposited on YT15 (WC + 15%TiC + 6%Co) cemented carbide. Microstructural and fundamental properties of these ZrN coatings were examined. Unlubricated sliding wear tests against hardened steel using the ring-block method were carried out with these ZrN coatings in air atmosphere. The friction coefficient and wear rates were measured with varying sliding speeds and normal loads. The wear surface features of the coatings were examined by scanning electron microscopy. Results showed that the deposition of the PVD ZrN coatings onto the YT15 cemented carbide causes great increase in surface hardness. The ZC-1 specimen (ZrN/YT15 without interlayer) has the highest surface hardness, while the ZC-2 (ZrN/Zr/YT15 with Zr interlayer) specimen showed the highest adhesion load for the coatings to the substrate. The ZrN coatings exhibit improved friction behavior and wear resistance to that of the YT15 cemented carbide. The specimens with a Zr interlayer (ZC-2) have higher wear resistance over the one without Zr interlayer (ZC-1). The wear patterns of the ZrN coatings observed were mainly abrasive wear at low sliding speed, while severe adhesive wear was found to be predominant at high sliding speed. Cracks and delamination fracture of the ZrN coatings from the substrate were observed at the highest load applied.