Reactive Ion Coating (RIC™) Using Titanium Nitride (TiN)

Liburdi Engineering's Reactive Ion Coating (RIC™) use titanium nitride (TiN)to deposit a thin, hard, layered ceramic film on turbine hot section components. The coating provides maximum erosion protection, prolonging component life and increasing life cycle efficiency for components.

The reactive ion coating can be applied to existing compressor designs without adverse affects on their mechanical or aerodynamic characteristics. The comparatively thin coatings do not alter the natural frequency of the blades and if properly applied should not reduce their fatigue resistance.

Titanium Nitride Coatings

In order to be effective, protective coating material must:

1. Have good erosion resistance properties. That is, it should have a hardness greater than sand, which is the principal erodent, and a toughness as high as possible to improve high-angle impact resistance.
2. Adhere well to the base metals and ideally should have a compatible coefficient of thermal expansion.
3. Be smooth and uniform in thickness, as well as capable of conforming to blade geometries and sharp edges, without additional grinding or polishing.
4. Be applied using a process that does not damage the substrate alloy by exposure to excessively high process temperatures or corrosive chemicals.

Titanium nitride has extremely high resistance to both high- and low-angle erosion providing better protection than other materials such as:

• Ceramic oxides (e.g., glasses and alumina). These have medium hardness but low toughness, and generally exhibit poor adhesion in thick layers.
• Plasma sprayed coatings (e.g., tungsten and chrome carbide). These tend to be heavy, thick, and have only moderate hardness. Sprayed coatings also generally have a rough surface that may influence the aerodynamic performance.
• Plated metals (e.g., nickel). These are smooth but only marginally harder than the base metals.

Engineered ceramics, (nitrides, borides, carbides) have very high hardness and toughness, coupled with low density and smoothness. TiN coatings also provide good adhesion to compressor materials.

Other coating types are primarily designed for corrosion protection or airfoil surface smoothing. They are typically applied as slurries or thick coatings, which can reduce the airflow area of small airfoils and may cause a significant shift in resonance frequency of blades. Any improvement in airfoil smoothness provided by these techniques is short-lived, because these soft coatings have poor erosion resistance characteristics, compared to ceramic materials or even base alloys.

Reactive Ion Coating (RIC™)

Liburdi Engineering's reactive ion coating (RIC™) process produces a coating that meets all of the criteria listed above. They provide high hardness, good toughness and a metal-like coefficient of thermal expansion. The relatively low density and thickness of the coating minimizes the possibility of resonant frequency shifts or aerodynamic surface effects.

Because the physical vapor deposition (PVD) process can coat complex geometries at low temperatures, RIC™ does not alter the microstructure and mechanical properties of most compressor alloys.
The RIC™ process is highly customizable to meet manufacturing and overhaul requirements. RIC™ can produce a wide range of microstructures and stoichiometries, which allows the coating to be optimized for erosion. Because the process uses an electron beam heated pool rather than an arc source, metallic splashes or defects are minimized. The electron beam can also melt various forms of stock materials and is not reliant on the more expensive pre-manufactured targets used by the arc and sputtering processes.

Reactive ion coatings can be safely removed from steel and nickel airfoils without any degradation to the airfoils surface finish, dimensional tolerances or microstructure.

   View the RIC™ TiN datasheet.