High temperature (900 °C) sliding wear of CrNiAlCY coatings deposited by high velocity oxy fuel thermal spray

Nickel based superalloy are in demand for high temperature applications and their corrosion, erosion and wear resistance have been investigated for a long time. Nickel chromium (NiCr) alloys are widely used for corrosion resistant coatings, while chromium carbide nickel chromium (CrC-NiCr) alloys are preferred for wear resistant coatings at high temperature. In this study CrNiAlCY coatings were deposited via a liquid fuelled high velocity oxy fuel (HVOF) thermal spray using two spray parameters and tested as wear resistant coatings. Effects of processing parameters on microstructure and mechanical properties of the coatings were investigated. Results showed that higher oxygen flow rates are critical for obtaining coatings with lower porosity and higher microhardness. Coating with lower porosity and higher hardness was chosen for both room temperature (~24 °C) and high temperature (900 °C) unlubricated sliding wear tests in a ball on disc setup. The coating was tested against alumina counterbody under 3 different loading conditions (10, 30 and 60 N). The wear rate of the coating was directly proportional to the applied load at room temperature. In the room temperature tests, wear debris was produced, which then oxidised and pushed away to the edges of the wear track. On the other hand, wear debris was smeared on the wear surface at high temperature tests. The surface was oxidised into Cr2O3 at high temperatures, which acted as a protective layer. Although thermal softening took place at higher temperatures, wear rates under 10 and 30 N were similar to room temperature values due to the protective oxide layer formed on the top surface; however, the oxide layer under 60 N could not withstand the load, started to crack and lost its protective ability.