Coating systems for Ni based superalloys Flashcards
1
Q
What do coating systems consist of
A
- Bond coat
- Thermally grown oxide
- Ceramic top coat
2
Q
What does the bond coat provide
A
provides oxidation and hot corrosion resistance
3
Q
What does the ceramic top coat provide
A
provide thermal insulation to the superalloy substrate
4
Q
What are the requirements of a coating system
A
- stable at the operating temperature
- have low thermal conductivity
- have coefficient of thermal expansion that is compatible with the substrate
- be resistant to oxidation and hot corrosion
- have acceptable fracture toughness
5
Q
How to obtain aluminide coatings
A
- by diffusion
- by plasma spray
- by electron beam-physical vapour deposition
6
Q
How thick are each part of bounding system
A
- bond coat: 75-150μm
- thermal grown oxide: 1-10μm
- ceramic top coat: 100-200μm
7
Q
What effect does adding Cr have
A
- increases hot corrosion and oxidation resistance
- limited by how much Cr-rich phases form in coating
8
Q
What effect does adding Al have
A
- controls oxidation resistance
- reduces coating ductility
9
Q
What effect does adding Si have
A
- increases resistance to cyclic oxidation
- reduces the liquidus of the coating and can effect phase stability
10
Q
What effect does adding Y or Hf have
A
- improves adherence of the Thermal grown oxide as it combines with sulphur and prevents its segregation to the oxide layer
11
Q
What effect does adding Re have
A
- improves isothermal and cyclic oxidation resistance and thermal fatigue
- resistance of spalling
12
Q
What effect does adding Ta have
A
- oxidation resistance
