Tribological behaviors of CrN/Cr3C2-NiCr duplex coating at elevated temperatures

Duplex coating, composing of a thick Cr3C2-NiCr interlayer and a top CrN film, were deposited by high velocity oxy-fuel (HVOF) and arc ion plating technologies, and the microstructure, mechanical properties and thermal shock resistance of the duplex coating were investigated compared to those of the single CrN film, as well as tribological behaviors at elevated temperatures. Results showed that the duplex coating exhibited high surface hardness, H/E and H-3/E-2 ratios, load-bearing capacity and adhesive strength due to the supporting of the Cr3C2-NiCr interlayer, which contributed to improve the wear properties of duplex coating sliding against Al2O3 ball. At 25 degrees C, the duplex coating had a higher friction coefficient and a relatively low wear loss, and the main wear mechanism was abrasive wear. As the temperature increased to 350 degrees C, the top CrN film of duplex coating was worn out totally. The severe mismatch of coefficient of thermal expansion (CTE) between Cr3C2-NiCr interlayer and substrate that might have a negative impact on wear resistance of duplex coating at high temperature. In addition, a large number of debris produced due to oxidation peeling of the coatings were compacted to form a thick transfer film during the sliding process, resulting in badly adhesive wear. The wear mechanisms were adhesive and oxidation wear accompanied with abrasive wear at high temperature (from 150 degrees C to 550 degrees C).