TiAlN-based coating architectures for enhanced solid particle erosion resistance

Abstract

Solid particle erosion (SPE) can severely damage the airfoils of aircraft engines, reducing thrust and increasing fuel consumption. Ti-based nitride coatings are a suitable solution to protect against SPE. However, an optimal coating architecture should control intrinsic stress development during coating deposition. In the present work, two coating systems were deposited on Ti-6Al-4V alloy by low duty cycle magnetron sputtering (LDMS): i) monolithic TiAlN coatings with different bias values applied across their thickness, and ii) multilayer coatings composed of alternating metallic TiAl and ceramic TiAlN layers. The coating thickness varies from 9.5 μm to 11.4 μm depending on the architecture. All the samples exhibit a cubic-TiN crystallographic structure and the stress-depth profiles indicate that the development of compressive stresses strongly depends on the coating architecture. High hardness (25–30 GPa) was observed for coatings with moderately stressed surfaces (2.1–3.8 GPa in compression), and improved scratch resistance (L_C2 > 26 N) was obtained for coatings with moderate-to-low stress profiles. In addition, the coating's erosion resistance is increased by up to two orders of magnitude (1.3 × 10⁵ μm/g) compared to the bare substrate (3.7 × 10⁷ μm/g) while using Al₂O₃ particles at a speed of 75 m/s. The examination of the eroded surface reveals a combination of brittle and ductile mechanisms involved in the SPE process. The differences in the erosion rate of the coatings are correlated to the index of brittleness and the residual stress depth profile.