High temperature erosion-corrosion behaviour of magnetron sputtered TiCr/TiCrN ultrathin multilayer thin films for gas turbine engine applications

Abstract

When the aircraft is operated in deserts or dusty areas, solid particle erosion (SPE) causes major damage to the gas turbine engine compressor blades. Similarly, when operating in a corrosive environment such as near sea, corrosion plays a major role. The corrosion process on pristine and eroded surfaces can be different. So, corrosion studies on eroded surfaces are important to understand compressor blade deterioration by erosion and corrosion. It is important to develop a coating that can protect the compressor blades from SPE and corrosion. Ternary nitrides are known to have a complementary effect of two different metal nitrides. Further, the multilayer coating architecture with altering mechanical properties across the thickness contributes to combat SPE and corrosion. Considering these key factors, nano-multilayered TiCr/TiCrN coating of thickness ~8.5 μm with a bi-layer thickness of 7.5 nm was developed using an in-house designed unbalanced magnetron sputtering system. The optimized coating exhibited good adhesion and mechanical properties. The SPE tests were carried out following ASTM-G76 standards in the temperature range of room temperature (RT) to 500 °C. The pristine and erosion-tested samples at impinging angles 30° and 90° were subjected to the potentiodynamic polarization tests in 3.5 wt% NaCl solution. The erosion test impingement angle and temperature impacted the corrosion behaviour of the substrate and the coating. The coating showed around ~93 times better erosion resistance than the bare Ti6Al4V substrate for 30 m/s erodent speed at 300 °C. The coated Ti6Al4V showed around two orders better corrosion protection than the bare Ti6Al4V. The high number of interfaces helped in restricting the corrosion media and the erosion crack penetration.