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:
- 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.
- Adhere well to the base metals and ideally should have a compatible coefficient of thermal expansion.
- Be smooth and uniform in thickness, as well as capable of conforming to blade geometries and sharp edges, without additional grinding or polishing.
- 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.