Super alloys for High temperature Applications

1. Super Alloys For High
Temperature Applications
Anand Mohan
M.Tech
IIT Kharagpur

2. INTRODUCTION
• A super alloy is an alloy that exhibits several key
characteristics like excellent mechanical strength,
resistance to thermal creep deformation, good
surface stability, and resistance to corrosion or
oxidation.
• The crystal structure is typically face-centered
cubic .
• Examples:- Hastelloy , Inconel , Waspaloy, Rene
alloys, Haynes alloys, Incoloy, MP98T, TMS alloys,
and CMSX single crystal alloys.

3. INTRODUCTION
• Super alloys develop high temperature strength
through solid solution strengthening
• Another important strengthening mechanism
is precipitation strengthening which forms
secondary phase precipitates such as gamma
prime and carbides.
• Oxidation or corrosion resistance is provided by
elements such as aluminium and chromium.
• Alloying increases the strength and temperature
capability.

4. PROPERTIES
• Heat resistant and high strength at high
temperature (760-980◦C).
• Good corrosion resistance.
• Good oxidation resistance.
• High toughness and ductility
• Good surface stability

5. CLASSIFICATION
• Super alloys are often classified into
generations and until today there were five
generations
• The sixth generation is in the form of project
at National Institute of Material Science in
Japan (NIMS)
• First generation super alloys are characteristic
with a relatively huge amount of chromium in
comparison with other generations

6. CLASSIFICATION
• The second and third generation contains about 3
wt % and 6 wt % of rhenium respectively
• Rhenium is a very expensive addition but leads to
an improvement in creep strength and fatigue
resistance
• As an example of fourth generation of super
alloys TMS-138 can be characterised.
• It was developed in NIMS with the addition of Mo
for increasing the lattice misfit .

7. CLASSIFICATION
• The representation of the fifth generation of the super
alloys is for example TMS-169 alloy developed at NIMS
in collaboration with Ishikawajima-Harima Heavy
industries co. Ltd (IHI) in japan in 2006
• TMS-169 is an advanced super alloy containing 5 wt %
Ru and 4.6 wt % Cr
• TMS 169 with superior high temperature creep and
oxidation resistance by incorporating further
Ruthenium and Cr content over the composition of
fourth generation alloys
• With Ru additions it will enhance the phase stability.

8. CLASSIFICATION
• Super alloys are classified into three based on
the predominant metal present in the alloy.
They are
Nickel based Super alloy
Iron based Super alloy
Cobalt based Super alloy

9. Nickel based Super alloy
• Nickel based Super alloys can be strengthened by
either Solid solution strengthening or
Precipitation hardening.
• Most Ni based alloy contain 10-20% Cr, up to 8%
Al and Ti, 5-10% Co, and small amounts of B , Zr
and C
• Other common additions are molybdenum,
niobium, and tungsten, all of which play dual
roles as strengthening solutes and carbide
formers.
• Chromium and aluminium improves surface
stability through the formation of Cr2O3 and Al2O3

10. Iron based Super alloy
• Iron based Super alloys are characterised by
high temperature as well as room
temperature strength.
• Apart from this, it will have good resistance to
creep , oxidation, corrosion and wear
• Oxidation resistance increases with chromium
content

11. Cobalt based Super alloy
• Cobalt based Super alloys have their origin in
the stellite alloys.
• Cobalt alloys have higher melting points than
nickel alloys .
• Cobalt alloys show superior thermal fatigue
resistance and weldability over the nickel
alloys.

12. APPLICATIONS
• Aerospace
– Turbine blades and jet/rocket engines
Intermediate pressure compressor (IPC),
High pressure compressor (HPC),
High pressure turbine (HPT),
Intermediate pressure turbine (IPT),
Low pressure turbine (LPT),
and the pressure and temperature
profiles along the engine.

13. APPLICATIONS
• Gas Turbine for marine propulsion

14. APPLICATIONS
• Pressurized water reactor vessel head

15. APPLICATIONS
• Gas Turbine at thermal power plants

16. APPLICATIONS
• Rocket Motor Engine

17. APPLICATIONS
• Turbine Blades (Jet Engine)

18. APPLICATIONS
• Engine and turbine of Superbikes

19. CHEMICAL DEVELOPMENT OF Ni-
BASED SUPER-ALLOY
• The properties of Ni based super alloys can be
tailored to a certain extent through the addition of
many other elements.
Effect Alloying Elements
Solid-solution strengtheners Cr, Mo
Fcc matrix stabilizers C, W, Ni
Carbide formers Ti,Cr,Mo
Forms γ' Ni3 (Al, Ti) Al, Ni, Ti
Retards formation of hexagonal η(Ni3Ti) Al,Zr
Hardening precipitates Al, Ti, Nb
Oxidation resistance Cr
Improve hot corrosion resistance La, Y
Sulfidation resistance Cr
Increases rupture ductility B

20. • Creep resistance is dependent on slowing the
speed of dislocation motion within a crystal
structure. In Ni based super alloys, the γ’-
Ni3(Al,Ti) phase present acts as a barrier to
dislocation motion. For this reason, this
γ’ intermetallic phase, when present in high
volume fractions, drastically increases the
strength of these alloys due to its ordered
nature and high coherency with the γ matrix.

21. • In order to improve the oxidation resistance of
these alloys, Al, Cr, B, and Y are added. The Al
and Cr form oxide layers that passivize the
surface and protect the super alloy from
further oxidation while B and Y are used to
improve the adhesion of this oxide scale to
the substrate.
• grain boundary strengthening is achieved
through the addition of C and a carbide
former, such as Cr, Mo, W, Nb, Ta, Ti, or Hf,
which drives precipitation of carbides at grain
boundaries and thereby reduces grain
boundary sliding.

22. MICROSTRUCTURE
• Gamma matrix, γ
• Gamma prime, γ'
• Gamma double prime, γ''
• Carbides
• Topologically close-packed (TCP) type phases

23. fcc Ni-rich matrix
– “γ phase”
Ni3Al
precipitates – “ γ’ phase “
(cuboid in shape)

24. Gamma Matrix (γ)
• It is continuous matrix is an FCC nickel-base
nonmagnetic phase that usually contains a
high percentage of solid-solution elements .
• Alloying elements found in most commercial
Ni-based alloys are, C, Cr, Mo, W, Nb, Fe, Ti, Al,
V, and Ta
• No phase transformation upto Tm

26. Gamma prime, γ'
• It is an intermetallic phase based on Ni3(Ti,Al)
which have an ordered FCC structure.
• In the γ´-phase the nickel atoms are at the
face-centers and the aluminium or titanium
atoms at the cube corners.

27. Gamma prime, γ'
• It precipitated as spheroidal shape or cuboidal
shape depending upon the volume fractions of
particles. Cuboidal precipitates were noted in
alloys with higher aluminium and titanium
contents.
• The change in morphology is related to a matrix-
precipitate mismatch. It is observed that γ' occurs
as spheres for 0 to 0.2% mismatches, becomes
cuboidal for mismatches of 0.5 to 1%, and is
plate-like at mismatches above about 1.25%.

28. Deformation properties of γ and
γ’ phases
• γ phase: ductile at all temperatures, moderate
strength which decreases with temperature
• γ’ phase: brittle except at very high
temperatures, very high strength which
increases with temperature up to ~ 1100 K
• The hard γ’ phase constrains dislocation
motion in the soft γ phase. Consequence: also
the γ phase gets stronger

29. Gamma double prime, γ''
• nickel and niobium combine in the presence
of iron to form body centered tetragonal (BCT)
Ni3Nb, which is coherent with the gamma
matrix, while including large mismatch strains
of the order of 2.9%.
• This phase provides very high strength at low
to intermediate temperatures, but is unstable
at temperatures above about 650 °C (1200 °F).

30. Crystal structure for γ" (Ni3Nb)
(Body Centered Tetragonal)

31. Carbides
• The common nickel-base alloy carbides are
MC, M23C6, and M6C. MC usually exhibits a
coarse, random, cubic, or script morphology.
• they are used to stabilize the structure of the
material against deformation at high
temperatures. Carbides form at the grain
boundaries inhibiting grain boundary motion

32. Carbides formed in super alloy Inconel 718

33. Topologically close-packed (TCP) type
phases
• if composition has not been carefully
controlled, undesirable phases can form either
during heat treatment or, more commonly,
during service. These precipitates are known
as TCP phases. Usually harmful, they may
appear as long plates or needles, often
nucleating on grain-boundary carbides.

34. Topologically close-packed (TCP) type
phases
• Nickel alloys are especially prone to the
formation of σ and μ. The formula for σ is (Fe,
Mo)x (Ni, Co)y, where x and y can vary from 1
to 7.
• The σ hardness and its plate-like morphology
cause premature cracking, leading to low-
temperature brittle failure, although yield
strength is unaffected .

35. HEAT TREATMENT
• Alloys are, first, solution treated to dissolve
nearly all γ' and carbides other than the very
stable MC carbides
• Typical solution treatments (for creep-limited
applications) are in the range of 1050 to 1200 °C
and may be followed by a second solution
treatment at lower temperature
• Some γ' can form upon air cooling from the
solution treatment temperature. Aging is then
carried out in several steps to coarsen the γ' that
is formed upon cooling, as well as to precipitate
additional γ'.

36. • A two-step aging treatment is commonly used,
with the first treatment in the range of 850 to
1100 °C over a period of up to 24 h.
• The finer γ' produced in the second aging
treatment is advantageous for tensile strength
as well as for rupture life.
• Both solution and aging anneals are followed
by air cooling
HEAT TREATMENT

37. • Carbide distribution also is controlled by the
heat treatment schedule. Modifications to the
γ' heat treatment procedure often are
required to avoid problems with carbide films
at grain boundaries.
• Therefore, a lower solution treatment
temperature (about 1075 °C) is used to
preserve the fine-grain as-worked structure
with well-dispersed M6C.
HEAT TREATMENT

38. Research and development of new
super alloys
• Sandia National Laboratories is studying a new
method for making super alloys, known
as radiolysis.
• It introduces an entirely new area of research into
creating alloys and super alloys
through nanoparticle synthesis.
• Future paradigm in alloy development focus on
reduction of weight, improving oxidation and
corrosion resistance while maintaining the
strength of the alloy.
• another focus is to reduce the cost of super alloys

39. REFERENCES
• Henkel and Pense , Structure and Properties of
Engineering materials, 5thedition.
• Prof. Diego Colombo, Nickel-based super alloys
and their application in the aircraft industry.
• Hiroshi Harada and Yuefeng GU, High
temperature materials
SUPERALLOYSSUPERALLOYS
• Reed, Roger C. The Super alloys: Fundamentals
and Applications. Cambridge, UK: Cambridge
University Press, 2006.

40. REFERENCES
• Minoru Doi et.al "Gamma/Gamma-Prime
Microstructure Formed by Phase Separation
of Gamma-Prime Precipitates in Ni-Al-Ti Alloys
• https://en.wikipedia.org/wiki/Superalloy
• http://www.phasetrans.msm.cam.ac.uk//200
3/Superalloys/superalloys.html

41. THANK YOU