How Aerospace Surface Treatments Protect Titanium Parts
It is worth noting that although Titanium is a corrosion resistant metal, it does not mean it does not need any surface treatment.
Why Titanium Still Needs Treatment
Titanium naturally forms a stable oxide layer when it is exposed to air. However, the oxide layer formed naturally by titanium offers little protection against galling, fretting fatigue, etc. Surface treatment to the titanium part addresses the above specific weaknesses without compromising the base material.
Anodising for Identification and Mild Protection
Titanium can be anodized in various colours by altering the voltage to produce a thin layer of oxide to approximately 10 microns. Titanium parts can be identified between different alloy grades or even be used to identify individual parts within a batch of similar parts. Although there is only mild corrosion resistance, there is some improvement in fretting resistance.
Thermal Spray for Wear Zones
High-velocity oxy-fuel (HVOF) spray coatings made of tungsten carbide are often used for wear situations on titanium parts. The resulting surface provides a hard and dense wear surface which cannot be achieved by the substrate material alone. Common applications are bearing housings and sliding contact surfaces.
PVD and Ion Vapour Deposition
PVD coating types such as Physical vapour deposition and ion vapour deposition produce extremely thin hard films which can be used to increase surface hardness of the part and reduce surface friction. Titanium nitride coating is typical of this type of coating and is used for components such as aerospace components that require close tolerance machining.
Masking and Dimensional Control
The precision machining of titanium components means that parts such as those with threads, bearing faces or other mating surfaces can need to be masked prior to surface treatment. Even a thin layer of coating can increase the dimension of a part and such parts are often made to very close tolerances on the titanium itself.
Treating parts as early as possible in their production can save costly rework of expensive parts.