super alloys

Question 1

what is a SUPER ALLOY

Answer 1

➢ A superalloy is a high temperature, heat resistant alloys that
are able to retain their mechanical strength & creep
resistance at high temperatures

Question 2

what does Cr do in super alloys.

Answer 2

substitutional solid solution and contributes to the strength in this way also contributing to oxidation resistance.

Question 3

what are the major phase in nickel based super alloys

Answer 3

gamma -
continuous matrix of fcc austenite
gamma prime-
this is the major precipitable phase(NI3 Al)
carbides-there are various types , mainly M23 C6 where M represents the metal.

Question 4

what is a coherent precipitate

Answer 4

gamma prime is one, and this is where the lattice of the precipitate and the matrix is continuous across the interface,
more desireable for high temp materials

Question 5

what are the different type of interfaces between solids

Answer 5

Coherent - there is perfect registry of the lattices.
* Coherent with strain - it is quite likely for there to be
some strain with the interface, due to imperfect
matching. The strain energy increases with the size of
the growing particle, and there is a transition to a
semi-coherent interface.
* Semi-coherent interface - the introduction of
dislocations reduces the strain energy (but they
themselves contribute to the energy of the system).
* Incoherent - there is no matching of the interface

Question 6

what are mono carbides

Answer 6

M_C where m stands for metal
“M” is usually Ti, Ta, Nb or W.
➢ They are very stable and form just below solidification temperature.
➢ They restrict grain growth during solution treatment.
➢ Blocky, needle like form, distributed sparsely well at GB

Question 7

in super alloys, what does mc and M23 C6 do to grain boundaries

Answer 7

“M”C & “M”
23C6 Carbide at grain boundaries often inhibit grain boundary
migration during deformation and thus enhance the fatigue performance of
superalloys

Question 8

in super alloys where do carbides form?

Answer 8

Carbides form on the grain boundaries and within the grains. Since carbides are hard and brittle, the
distribution on the grain boundaries will particularly affect the high temperature strength, the ductility and
the creep properties of the alloy.