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1. CASE STUDY
Failure of a Low-Pressure
Turbine Rotor (LPTR) Blade
Dr. Muhammad Ali Siddiqui

2. Content
 Background with literature review about super alloys,
properties, alloy design and manufacturing process
 Testing Procedure and Results
Visual Examination of General Physical Features
Scanning Electron Microscopy and Fractography
Metallography and Hardness
 Discussion
 Conclusion
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3. Background and Literature Review
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4. • Fracture: low-pressure turbine blade  causing extensive
damage to the Jet engine.
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Source: https://www.wikiwand.com/en/Turbine_blade

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Ni

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Ni
Al
Ni Al
Thermodynamic favour ordered structure

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70% of intermetallic make it suitable for
applications

17. Other Alloying
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Source: https://www.semanticscholar.org/paper/High-temperature-materials-for-aerospace-Ni-based-Perrut-
Caron/9fa926f08f061dc68b29ebe7b4bfdfb7a60c56bf
https://doi.org/10.1016/j.crhy.2018.10.002

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Investment (lost wax) casting
Materials 2019, 12(11), 1781; https://doi.org/10.3390/ma12111781

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ceramic topcoat is
deposited by electron beam
physical vapor deposition
(EBPVD) or air plasma-
spraying (APS)
Sandwiched between the
topcoat and the metallic
bond coat is the thermally
grown oxide (TGO)
Surface treated: THERMAL-BARRIER COATINGS (TBCs)
Examples: Aluminide coatings

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First stage (the stage directly following the combustor) of a modern gas turbine
faces temperatures around 1,370 °C
Modern military jet engines, like the Snecma M88, can see turbine temperatures
of 1,590 °C.
Cross sectional view

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29. Case Study
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30.  LPTR blade failed
 Ni-base superalloys
 causing extensive damage to the engine.
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Background

31. Visual Examination
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Observation:
•Fractured = Airfoil section at a
distance of about 25 mm from the
blade root platform
•The fracture surface was flat and
perpendicular to the blade axis.
Fig : Photograph of the failed LPTR blade

32. Low magnification Examination
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Fig : Entire fracture surface
Observation:
Discolored  due to oxidation
and exposure to high temperatures
well-defined crescent-shaped
area with smooth fracture
features  Fatigue features
Fatigue crack found at leading
edge.
 Remaining fracture surface had a
crystalline appearance

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Intergranular = 1 mm from
the leading edge
Transgranular = 11 mm
SEM and Fractography
Fig: Intergranular fracture at the
leading edge
Fig: Beach Marks
Fig: striations

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Metallography and Hardness
Fig: Microstructure at leading edge
Fig: Microstructure at midcord
Observation:
precipitates dissolution at the leading edge.
At the leading edge 350 HV
At the mid-chord section 400 HV

35. Discussion
1. Failure Mechanism:
• Intergranular mode (IM) to about 1 mm from the leading edge
• Followed by a transgranular mode (TM) of about 11 mm
– IM Principal mode in high-temperature creep/stress rupture.
– Cracking occur principally along the grain boundaries normal to the
major stress axis of the blade.
– TM The incremental crack growth is evidenced by the presence
of closely spaced striations.
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36. • Therefore, it appears that the crack initiated at the leading edge
of the blade by stress rupture and propagated fast to a distance of
about 1 mm.
• In the second stage, this crack acted as a notch for stress
concentration and led to the propagation of the crack by fatigue.
• The fatigue crack then propagated progressively up to about 11
mm from the leading edge before giving way to overload fracture.
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Cont…

37. 2. Cause of Failure:
• Dissolution of gamma prime (γ-prime)
precipitates at the leading edge clearly indicates
that the blade was exposed to high temperatures
 the hardness  the creep resistance of
the blade drastically.
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38. Conclusion
• The cracking of the blade took place by stress rupture.
• Once the initial crack had formed due to stress rupture, the crack further
propagated under the cyclic loading experienced by the blade during
service.
• The factors responsible for such cracking are high operating temperatures
and stresses that causes the dissolution of the precipitates.
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39. Thank You
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