Today's advanced materials in manufacturing industries

1. DEVELOPMENT OF ADVANCED MATERIALS
AND MANUFACTURING TECHNOLOGIES FOR
HIGH EFFICIENCY GAS TURBINES
Turbine Blades
1
Naveen Chandra
17MTRAP013

2. What are the turbine blades made of?
A turbo jet engines works in a very hostile environment. Exhaust
gases that drive the turbine can sometimes exceed 1500°C and are
very corrosive. The turbine disc, is located in a high-velocity jet of
those gases. The turbine blades of jet engines work in similar or
worse conditions from around 1200°C upwards. Moreover, the
rotor system on many turbochargers operate in excess of 100 000
RPM. Huge tensile loads result from the centrifugal forces, in
addition to vibrational and bending loads. Thermal shock and
Creep are also issues. Nickel-based superalloys are therefore used
for such turbine discs. These alloys retain high strength values
even at high temperatures. Typical turbines are investment-cast
from Inconel 713 C or 713 LC and turbine wheel castings can be
treated with Hot Isostatic Processing (HIP) for improved structure,
then heat-treated for the required strength
22

3. Turbine Inlet Temperatures V/s
Time Period
3

4. What is the Problem?
A turbine blade is subjected to huge centrifugal load, which will
be one of our critical factors in selecting the material. The blades
also must not fail due to bending during sudden turbine
acceleration or vibrations. This requires high strength and
Resistance to brittle failure.
For the centrifugal forces, we look for high strength in
combination with low density for this particular application.
Tensile strength, Yield strength or Fatigue strength are possible
mechanical properties to consider.
The cyclic load does not refer to the rotations of the turbine, as
one might think, but rather to the load caused by frequent and
repetitive starts, stops, thermal shocks etc.
4

5. Mitsubishi Heavy
Industries, Ltd. (MHI) Research & Innovation
Center,Japan
With a view to building 1700°C-class gas turbines, MHI Research &
Innovation Center conducted joint research with the National Institute for
Materials Science (NIMS) to develop highly heat-resistant materials for
single-crystal blades. It is essential to not only verify the material strength
at high temperatures, but also develop a casting technology to obtain a
good monocrystalline structure with no defects. The new
material should also be satisfactory in terms of economy including raw
material and casting costs. It also needs to exhibit all the required material
properties at high temperatures (e.g., creep strength, thermal fatigue
strength and oxidation resistance). Especially challenging was the
development of technology to realize the coexistence of creep strength and
thermal fatigue strength. 5

6. Thermal barrier coating Technology: Improved
Performance of Rolls-Royce Engines
In 1997, the Advisory Group for Aerospace Research and Development
(AGARD) head quartered in France organised a specialist workshop to
review thermal barrier coating (TBC) technologies.
Thermal barrier coating (TBC) systems have improved thermal efficiency
in gas turbines. Low-K TBCs will save 14MtCO2e over the 20 year life of
the engine. Adjustment for the effect of emissions at high altitude
increases the calculated benefit to 26.6MtCO2e. In fuel costs, this saves
operators £1.8 billion over the REF14 period considered and £3.4 billion
over the engine lifetime.
6

7. 7

8. Results of TBC Technology
Generally,low thermal conductivity (low K) barrier coatings,
developed at Cranfield, reduce specific fuel consumption by over 1%.
Commercial variants are now implemented on the Trent 1000, used to
power the Airbus 380, and the Trent XWB, the new engine to power
the Boeing Dreamliner aircraft.
The increase rate of the gas turbine inlet temperature is far greater than
that of the upper temperature limit of superalloys. This rapid increase
in inlet temperature has been managed by improving cooling and
coating technologies. The latest 1600°C-class Type J gas turbines have
adopted the advanced TBC, which was developed as part of the
national project.
8

9. Underpinning Research
In 1997, the thermal conductivity of an EB-PVD thermal barrier
coating was reported as 1.8-2.0W/mK. Cranfield’s research into
improved manufacturing methods, particularly the EB-PVD process
route, and the microstructure and chemistry of the coatings
produced, saw this drop to 1.65W/mK for a 200μm thick TBC
Later, research into various Lanthanide additions, including Erbium,
Ytterbium, Neodynium, and Gadolinium, and the combined use of
Multiple Lanthanide group oxides saw this reduce to 1.2W/mK,
Through tertiary and quaternary element size effects further altering
Phonon and photon scattering within the ceramic layer, thus lowering
the thermal conductivity
9

10. Blade Aerofoil coated with a low k thermal barrier
doped with erbia at cranfield
10

11. Further Advancements in TBC
Recently,Cranfield developed periodically layered TBCs, using a multiple
source with jumping beam electron beam evaporation methods, through
the modification of the nanostructure. This has resulted in a further
reduction in thermal conductivity, now achieving 0.9-1.0W/mK. The most
recent extension to this work uses the phosphorescent properties of
Lanthanide oxides when in a suitable host lattice such as Zirconia. This
has permitted the development of ‘self diagnostic’ TBC systems. Through
the adoption of Cranfield’s ‘low K’ thermal barrier coating technologies,
the thermal conductivity of such EB-PVD TBCs is reduced from 1.8
2.0W/mK to 1.0-1.2W/mK, permitting a 170 C temperature drop across
the 200μm thick EB-PVD TBC. 11

12. Conclusion
12
A series of new multi-layered coatings for engine test have been
produced by Cranfield and have been run in Rolls-Royce development
engines, proving the technology for incorporation in
future high performance Trent family (Trent 1000 and Trent XWB)
engines