Nickel base superalloys

1. SUPERALLOYSSUPERALLOYS
N. PRAKASAN
ME METALLURGY

2. SUPERALLOYSSUPERALLOYS
INTRODUCTION
 Nickel-based superalloys possess good
combinations of high-temperature mechanical
properties and oxidation resistance up to
approximately 550°C.
 High temperature heat-resistance alloys, which can
retain high strengths at elevated temperatures.
 Alloying increases the strength and temperature
capability but reduces the processability.

3. SUPERALLOYSSUPERALLOYS
PROPERTIES
Heat resistant and high strength at high
temperature (760-980o
C).
Good corrosion resistance.
Good oxidation resistance.
High toughness and ductility
Excellent cryogenic temperature properties.

4. SUPERALLOYSSUPERALLOYS
CLASSIFICATION
There are three types of Ni-base superalloys:
• Nickel base,
• Nicke-lron base,
• Cobalt base.
The alloys contain high Cr with Ti, Al to from
precipitates and additions of Mo, Co, Nb, Zr, B,
Fe.

5. SUPERALLOYSSUPERALLOYS
MICROSTRUCTURE
The major phases present in the nickel-base
superalloys:
γ (gamma) phase – the continuous matrix of
FCC austenite.
γ’ (gamma prime) phase – the major
precipitate phase (more cubic shape).
Carbides –various types, mainly M23C6 and
MC. (M = metal).

6. Three strengthening mechanisms
are used in Ni superalloys:
· Solid solution hardening
· Coherent precipitate
hardening
· Carbide phases on grain
boundaries
STRENGTHENING MECHANISMSTRENGTHENING MECHANISM
SUPERALLOYSSUPERALLOYS

7. SUPERALLOYSSUPERALLOYS
Solid solution strengthening
• Cr, Mo, Al, Nb, Ti and others
Precipitation strengthening
• Mostly due to Al and Ti
• Ni3(Al,Ti), gamma prime
Carbide phases
• M23C6, M6C or MC
STRENGTHENING MECHANISMSTRENGTHENING MECHANISM

8. SUPERALLOYSSUPERALLOYSMICROSTRUCTUREMICROSTRUCTURE

9. SUPERALLOYSSUPERALLOYS
MICROSTRUCTURE
A two-phase equilibrium microstructure is
generated, consisting of gamma γ and gamma-
prime (γ´)
Both phases are face-centered-cubic, have
almost identical lattice dimensions and also
similar orientation. Consequently the two
phases are almost coherent.
The lattice sites in the γ-phase are totally
equivalent and the atoms constituting the solid
solution being distributed randomly.

10. MICROSTRUCTUREMICROSTRUCTURE
In the γ´-phase (Ni3(Al,Ti) ) the nickel atoms
are at the face-centers and the aluminium or
titanium atoms at the cube corners.
• The close match in matrix/precipitate lattice
parameter (~0-1%) combined with the
chemical compatibility allows the γ´ to
precipitate homogeneously throughout the
matrix and has a long-time stability.
SUPERALLOYSSUPERALLOYS

11. MICROSTRUCTUREMICROSTRUCTURE
 Carbides
 The added content of carbon is approximately 0.05-
0.2%.
 In combination with reactive and refractory elements
such as titanium, tantalum, and hafnium it forms
carbides (e.g., TiC, TaC, or HfC).
 During heat treatment these carbides begin to
decompose and forms lower carbides such as M23C6
and M6C, which tend to generate on the grain
boundaries.
 The mainly M elements in M23C6 are chromium, iron,
tungsten and molybdenum.
SUPERALLOYSSUPERALLOYS

12. EFFECT OF ALLOYING ELEMENTSEFFECT OF ALLOYING ELEMENTS
SUPERALLOYSSUPERALLOYS

13. SUPERALLOYSSUPERALLOYS
CHEMICAL COMPOSITION
Most nickel-based alloys contain 10-20% Cr,
up to 8% Al and Ti, 5-10% Co, and small
amounts of B, Zr, and C.
Chromium and aluminium are necessary for
oxidation resistance.
The elements such as C, Cr, Mo, W, C, Nb,
Ta, Ti and Hf form carbides.

14. SUPERALLOYSSUPERALLOYS
CHEMICAL COMPOSITION
Elements which stabilize the grain boundary
are B, C, and Zr. Their atomic diameters differ
from Ni by 21-27%. The resulting reduction in
grain boundary energy is associated with
better creep strength and ductility.
The elements Co, Fe, Cr, Nb, Ta, Mo, W, V, Ti
and Al are also solid-solution strengtheners,
both in γ and γ' phase.

15. SUPERALLOYSSUPERALLOYS
Ni-Iron Superalloys
Fe is added to replace some of Ni as it has
lower cost.
Ni-Fe superalloys contains 25-45%Ni and 15-
60%Fe.
Microstructure consists of austenistic FCC
matrix and can be strengthened by solid
solution strengthening (Mo, Cr), and
precipitation hardening (Ti, Nb, Al) by forming
intermetallic phases.
Examples: Inconel 707, 718, 901.

16. SUPERALLOYSSUPERALLOYS
SUPERALLOY GRADES

17. Applications:
 Aerospace Gas Turbine Engines
 Space vehicles - Rocket engines,
 Nuclear reactors
 Power Generation Turbines
 Submarines.
 Petrochemical equipment.
 High-Temperature Fasteners
 Combustion Engine Exhaust Valves
 Hot Working Tooling and Dies,
SUPERALLOYSSUPERALLOYS

18. SUPERALLOYSSUPERALLOYS

19. REQUIREMENTS FOR COMBUSTION ZONE
TURBINE BLADES
SUPERALLOYSSUPERALLOYS

20. NI BASE SUPERALLOY TURBINE BLADENI BASE SUPERALLOY TURBINE BLADE

21. REFERENCES:
 Henkel and Pense, Structure and Properties of
Engineering materials, 5th
edition.
 Loren A. Jacobson, Physical Metallurgy_class notes
 Prof. Diego Colombo, Nickel-based superalloys and
their application in the aircraft industry.
 Hiroshi Harada and Yuefeng GU, High temperature
materials
SUPERALLOYSSUPERALLOYS