High performance alloys

Question 1

what is the three phases occuring within nickel superalloys and how do the phase contribute to its strengthening properties?

Answer 1

three phases are gamma, gamma prime and carbides. gamma is a matrix of fcc austenite (increased temperature creep resistance). gamma prime major precipitate phase. carbide phase prohibits the grain growth during solution treatment.

Question 2

what is a super alloy?

Answer 2

a super alloy is high temp resistant alloy that has high mechanical strength and creep resistance at high temp.

Question 3

Effects of carbides on grain boundar?

Answer 3

If there is no carbodes on the grain it can cause sliding and creep.
if there is too much it can create a brittle fracture path.
perfect amount is a discontinuous carbide chain.

Question 4

What is the mechanical differences between nickel and cobalt alloys?

Answer 4

Ni are higher strength but cobalt maintain strength at higher temps.

Question 5

What are the types of super alloy castings?

Answer 5

Conventional casting (using standard mould and allowed to cool, grain growth from walls)

Directionally Solidified casting (Grains are initiated from the bottom cooled surface and grow upwards, eliminating transverse boundaries)(stronger than regular casting)

Single crystal casting (corkscrew/pigs tail shape, one grain grows)(resistant to thermal shock and creep)