Superalloys - Powder Metallurgy

Question 1

What is the benefit of using powder mettalurgy?

Answer 1

You tend to get a higher fraction gamma prime

You can create more complex alloys

Question 2

As PM is more expensive than cast and wrought alloys what type of components is it used for?

Answer 2

Critical components, such as turbine discs. This is due to:

• Lower levels of segregation
• finer grain structure
• reduced defect concentration

Question 3

What is the PM process?

Answer 3

• Vaccum induction melt of ingot
• Remelt and atomise (using argon gas)
• Particles degassed, sieved, canned and sealed
• Hot isostatic press (1000 degrees and 100MPa for 4 hours)
• OR extrude and force

Question 4

What are the property requirements of turbine discs?

Answer 4

Depends on the location.
At the bore the temperatures are low but stress is very high and so tensile strength is required
At the rim where the blades are supported it is the hottest, therefore creep resistance is required.