Paper SE-ThA8
Erosion Resistant Coatings Inside Narrow Tubes to Protect Aircraft Engine Components

Thursday, October 24, 2019, 4:40 pm, Room A215

There is an ever-growing interest in the use of functional coatings to protect surfaces of materials and workpieces against harsh environments such as corrosion, abrasion or solid particle erosion (SPE), making surface engineering solutions a very attractive balance between performance and cost. Numerous vapor-based fabrication techniques have been developed, namely PVD, CVD and PECVD, that can be used to achieve high hardness and high wear resistance, while being compatible with substrate materials such as metals, and different substrate shapes. This is increasingly important in the case where there is a need for protective coating solutions for inner surfaces of tubular components, such as parts of aircraft engines, oil pipelines, mining components, and numerous others. Specifically, certain aircraft diffusers are designed to conduct the air to the combustion chamber by means of many narrow gas inlets arranged around a circular frame. In such case, SPE arising from dust particles and volcanic ashes present in the air can result in an increase of the gas inlets diameter, leading to back streaming of air into the compressor (known as the compressor surge), which can give rise to significant aircraft engine damage and catastrophic consequences.

In response, we propose a novel Non-Line-Of-Sight (NLOS) technique to coat the inner parts of non-linear surfaces and cavities with hard, wear- and erosion-resistant coatings possessing high erosion resistance, hardness significantly higher than the hardness of the particles impacting the surface, as well as a large thickness (preferably 8 µm and more).

Specifically, we review, study and demonstrate the fabrication process of hard SPE-resistant TiN protective coatings on the inner surfaces of narrow tubes using a non-obvious NLOS approach yielding a uniform film thickness and properties along the tube axis (better than 20%). The deposition process indicates the importance of applying pulsed-DC PECVD, when uniform hard TiN films are prepared at low-frequency in the several kHz range. The TiN films (about 12 µm thick), exhibit high hardness and Young’s modulus (25 and 225 GPa, respectively), corresponding to the (111) preferred crystallographic orientation. We show that the SPE resistance on the inner surface decreased by a factor of more than 15 compared to the bare substrate, and that the process is well suited for the protection of aerospace, manufacturing, 3D printed and other critical components with a complex shape of inner surfaces.