Low Pressure and Vacuum Plasma Spray Coating Processes for Aero and Space Engine Applications

Increasing requirements on aerospace and space engine (turbine, rocket) performance has necessitated continued development in refractory metal and thermal barrier bond coating systems.  Refractory metals may be provided in bulk (near-net shape) or as coatings.  Bond coatings in TBC systems involve a ceramic top coating over an applied superalloy bond coating. AMT AG and its USA partner Advanced Materials & Technology Services, Inc. build low pressure, vacuum plasma, and hybrid systems for producing refractory metal and bond coatings for TBC systems.  

Superalloy and refractory metal (niobium, tantalum) coatings are produced with less oxides and porosity, and higher density (99%) in a low pressure and vacuum as compared to ambient air pressure.  Nickel-based bond coatings have shown enhanced oxidation protection and increased resistance to spallation, as compared to air plasma spray applied bond coatings. 

Coatings and/or bulk material may be produced ranging from vacuum (VPS) batch operations to- continuous low pressure plasma coating (LPCS) systems.  LPCS processes may be operated at higher power levels (e.g., 120 kW) using 03C2 plasma guns, whereas VPS processes are conducted at lower power (55 kW) with F4 plasma guns.  Hybrid systems will be shown consisting of a combination of these systems.  Process and configuration differences between VPS, LPCS and hybrid systems will be examined.  Superalloys and refractory metals will investigated between vacuum and air plasma spray (APS).  TBC coatings will be produced with vacuum, low pressure and APS systems.   

Microstructural analysis will be conducted evaluating coating buildup, oxides and porosity using optical and scanning electron microscopy.  Production rates, process rates and other items of relevance between these processes will be discussed.