Eddy Current Testing in the Quantitive Assessment of Degradation State in MAR247 Nickel Superalloy with Aluminide Coatings

Abstract

In this paper, the effectiveness of the eddy current methodology for crack detection in MAR 247 nickel-based superalloy with aluminide coatings subjected to cyclic loading was investigated. The specimens were subjected to force-controlled fatigue tests under zero mean level, constant stress amplitude from 300 MPa to 600 MPa and a frequency of 20 Hz. During the fatigue, a particular level of damage was introduced into the material leading to the formation of microcracks. Subsequently, a new design of probe with a pot core was developed to limit magnetic flux leakage and directed it towards the surface under examination. The suitability of the new methodology was further confirmed as the specimens containing defects were successfully identified. The changes in probe resistance values registered for damaged specimens ranged approximately from 8 to 14%.

Full text

Journal of Nondestructive Evaluation (2024) 43:112
https://doi.org/10.1007/s10921-024-01129-x
been specically designed to meet the demanding require-
ments of modern aircraft engines, where components must
withstand extreme temperatures, pressures, and harsh
environments while maintaining structural integrity and
reliability [1]. The alloy’s superior high-temperature perfor-
mance, combined with its excellent resistance to oxidation
and corrosion, make it an ideal material for critical engine
components such as turbine blades, vanes, and combustion
chambers [2]. However, a key challenge in the application
of these alloys is their susceptibility to oxidation and deg-
radation at elevated temperatures, which can signicantly
deteriorate their performance and limit service life [3]. To
address this issue, aluminide coatings have emerged as a
promising solution, oering enhanced protection against
oxidation and other environmental factors [4]. These coat-
ings form a protective layer of aluminium oxide (Al2O3) on
the surface, which acts as a barrier against oxygen and other
corrosive species. Aluminide coatings have become a widely
adopted solution to safeguard gas turbine blades made of
superalloys from the detrimental eects of high-temperature
oxidation and corrosion [5]. However, the performance and
integrity of these coatings are challenged by the complex
operating conditions experienced by gas turbines, including
cyclic thermal and mechanical loading [4, 5]. The fatigue
behavior and cracking of uncoated and coated MAR-M247
superalloy vary signicantly between room temperature and
1 Introduction
The MAR247 nickel superalloy has been extensively uti-
lized in the aerospace industry due to its exceptional
mechanical properties, high-temperature resistance, and
superior corrosion resistance. This nickel-based alloy has
Mateusz Kopec
mkopec@ippt.pan.pl
Grzegorz Tytko
grzegorz.tytko@polsl.pl
Małgorzata Adamczyk-Habrajska
malgorzata.adamczyk-habrajska@us.edu.pl
Yao Luo
luoyao@whu.edu.cn
1 Faculty of Automatic Control, Electronics and Computer
Science, Silesian University of Technology, Gliwice
44-100, Poland
2 Faculty of Science and Technology, University of Silesia,
Chorzów 41-500, Poland
3 School of Electrical Engineering and Automation, Wuhan
University, Wuhan 430072, China
4 Institute of Fundamental Technological Research Polish
Academy of Sciences, Pawińskiego 5B, Warsaw
02-106, Poland
Abstract
In this paper, the eectiveness of the eddy current methodology for crack detection in MAR 247 nickel-based superalloy
with aluminide coatings subjected to cyclic loading was investigated. The specimens were subjected to force-controlled
fatigue tests under zero mean level, constant stress amplitude from 300 MPa to 600 MPa and a frequency of 20 Hz. Dur-
ing the fatigue, a particular level of damage was introduced into the material leading to the formation of microcracks.
Subsequently, a new design of probe with a pot core was developed to limit magnetic ux leakage and directed it towards
the surface under examination. The suitability of the new methodology was further conrmed as the specimens contain-
ing defects were successfully identied. The changes in probe resistance values registered for damaged specimens ranged
approximately from 8 to 14%.
Keywords Nickel alloys · Aluminide coating · Non-destructive testing · Eddy current testing
Received: 8 July 2024 / Accepted: 21 September 2024 / Published online: 5 October 2024
© The Author(s) 2024
Eddy Current Testing in the Quantitive Assessment of Degradation
State in MAR247 Nickel Superalloy with Aluminide Coatings
GrzegorzTytko1· MałgorzataAdamczyk-Habrajska2· YaoLuo3· MateuszKopec4
1 3
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Journal of Nondestructive Evaluation (2024) 43:112
elevated temperatures. At room temperature, the uncoated
MAR-M247 typically exhibits good fatigue resistance due
to its inherent strength and microstructural stability, with
fatigue cracks generally initiating at surface defects or
inclusions and propagating slowly [6]. When coated, the
fatigue life may change depending on the coating material
and quality; a well-adhered coating can provide additional
protection against surface damage, delaying crack initia-
tion [7, 8]. However, at elevated temperatures, the fatigue
resistance of MAR-M247 decreases due to thermal soften-
ing and oxidation, which can accelerate crack initiation and
growth [9]. Coatings can mitigate these eects by providing
a thermal barrier and oxidation protection, thereby enhanc-
ing fatigue life. Nonetheless, coating defects or dierences
in thermal expansion between the coating and substrate may
introduce stress concentrations, potentially promoting crack
formation under cyclic loading at high temperatures.
The development of advanced material systems for gas
turbine applications has been a critical research focus, as
designers strive to push the limits of inlet gas temperatures
beyond 1300 –1400 °C [5]. The application of coatings on
the internal airfoil surfaces has enabled signicant improve-
ments in heat removal capabilities, projected to be over
50–70% compared to conventional smooth-channelled,
internally cooled airfoil congurations [10]. However, the
integrity of these coatings, which are critical to the reliability
of gas turbine blades, is challenged by the complex operat-
ing conditions experienced during operation. The demand-
ing service environment necessitates the regular inspection
of gas turbine blades, enabling a signicant reduction in
the risk of failures [11]. Non-destructive testing methods
can provide valuable insights into the integrity of thermal
barrier coatings on nickel-based alloys. These techniques
enable for precise detection of defects, corrosion, and other
imperfections without causing damage to the materials,
which is time-saving and cost-eective [12]. By leverag-
ing non-destructive testing, one can ensure the quality and
performance of coated components while maintaining their
structural integrity. The multilayer coating-substrate struc-
ture and limited access to turbine components expose signif-
icant challenges in developing a cost-eective and ecient
non-destructive method [13].
In the case of the ultrasonic method [14–16], the most
common inconveniences are related to the application of
coupling medium, which extends the test time and increases
its cost, and the elimination of the dead zone for shallowly
located defects. In other methods, the challenge is to ensure
sucient sensitivity, short inspection time, and easy inter-
pretation of results. Therefore, the novelty of this work lies
in the development of a new method, that meets all of these
requirements enabling eective detection of defects in gas
turbine blades. In the rst step, the microstructure of coated
MAR 247 nickel-based superalloy subjected to cyclic load-
ing was examined using light microscopy and scanning
electron microscopy SEM. This allowed for the determi-
nation of the shape, size, and location of damages result-
ing from intensive exploitation due to fatigue. The shallow
depth of critical damages and their relatively large quantity
led to the selection of eddy current technique for further
investigations. The required sensitivity was achieved by
constructing a probe with a pot core diameter corresponding
to the blade width at its narrowest point, as it is the most
susceptible to crack detection. The application of a pot core
enabled the limitation of magnetic ux leakage and directed
it towards the surface under examination. Tests were con-
ducted on MAR247 nickel superalloy, onto which coatings
of dierent thicknesses of 20 μm and 40 μm were applied.
The damage to the coatings and substrates was induced by
subjecting the specimens to fatigue tests at dierent stress
amplitudes. It leads to the formation of damage similar to
those during industrial turbine operation. Subsequent eddy
current method investigations involved measuring the probe
resistance for defect-free specimens and those subjected to
fatigue tests. The specimens containing defects were suc-
cessfully identied in all cases, and the resulting change
in probe resistance values ranged approximately from 8 to
14%.
One should highlight, that the novelty of this paper is
expressed by the development of a new methodology
enabling eective detection of defects in gas turbine blades.
This method employs an eddy current probe with the fol-
lowing advantages: the application of a pot core enabled the
limitation of magnetic ux leakage and directed it towards
the surface under examination (high sensitivity); the outer
diameter of the pot-core coil was chosen to be slightly
smaller than the width of the inspection area of 15 mm. This
reduced the inuence of the edge eect on changes in the
probe’s resistance and facilitated the precise placement of
the probe on the examined specimen; the pot-core coil was
placed in a head improving the probe’s stability; the narrow
range of optimal frequency values means that the operating
frequency of the probe only needs to be determined once.
Therefore, a signicant acceleration of the inspection pro-
cess could be achieved.
2 Materials and Methods
MAR 247 nickel superalloy specimens with three dier-
ent initial microstructures represented by ne (Fig. 1a),
coarse (Fig. 1b) and column (Fig. 1c) grains were manu-
factured during a conventional casting process. The average
grain size these structures was around 0.5 mm, 2.5 mm and
5 mm, respectively. The chemical composition of MAR247
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Journal of Nondestructive Evaluation (2024) 43:112
nickel superalloy was presented in Table 1. Aluminide coat-
ings were deposited during the Chemical Vapour Deposi-
tion (CVD) process. The deposition process was performed
at the temperature of 1040 °C and internal pressure of 150
mbar using optimised CVD parameters under the hydro-
gen protective atmosphere, with deposition times of 8 and
12 h for the coating thickness of 20 μm and 40 μm, respec-
tively. Exemplary cross-section of the MAR 247 specimen
with 40 μm coating was presented in Fig. 1d. It reveals a
two-layer structure consisting of a homogeneous zone of
secondary solid solution of the β (NiAl) phase and heteroge-
neous NiAl matrix (dark grey) with Ni3Al phase dispersions
(bright grey). The microstructural observations were carried
out using a JEOL6360LA scanning electron microscope
(SEM) operated at 20 kV with EDS detector.
The MAR 247 nickel superalloy specimens with ne,
coarse, and columnar grain structure and coatings of 20 μm
and 40 μm thickness [17] were subjected to testing using the
eddy current method [18–22]. By inducing electromagnetic
currents in the material, eddy current testing can detect
surface and subsurface defects, such as cracks, voids, and
delaminations, without direct contact. This method is sensi-
tive to variations in coating thickness [23–26], conductiv-
ity [27–31], and material properties [32, 33], allowing for
detailed and accurate evaluation of the coating’s integrity.
In the examination of large-scale objects, air-core coil eddy
current probes are often used [34–37]. The sensitivity of
such a probe is not sucient for detecting small cracks dur-
ing inspection of narrow areas. Therefore, a dierent solu-
tion was proposed as follows. The developed probe consists
of a coil placed inside a ferrite pot core [38–41]. The appli-
cation of the core reduced magnetic ux losses and directed
it directly towards the surface of the coating. The outer
diameter of the pot-core coil, which was equal to 14.5 mm,
was chosen to be slightly smaller than the width of the
inspection area of 15 mm. This reduced the inuence of the
edge eect on changes in the probe’s resistance and facili-
tated the precise placement of the probe on the examined
Table 1 Chemical composition of MAR 247 superalloy (wt%) [17]
C Cr Mn Si W Co Al Ni
0.09 8.80 0.10 0.25 9.70 9.50 5.70 bal.
Fig. 1 Initial microstructures of the MAR 247 nickel-based superalloy of ne (a), coarse (b) and column (c) grain structure; cross-section of the
MAR 247 specimen with 40 μm coating (d)
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Journal of Nondestructive Evaluation (2024) 43:112
in Fig. 3. These specimens were subsequently subjected to
cyclic loading using the MTS 810 testing machine. Fatigue
tests were force-controlled under zero mean level, constant
stress amplitude, frequency of 20 Hz and stress amplitude
ranging from 300 MPa to 600 MPa. Such fatigue testing
was performed at room temperature to introduce a specic
level of damage similar to those during industrial turbine
operation. In this research, the 0.5Nf was used as a refer-
ence point to interrupt fatigue tests in order to perform EC
measurements. Subsequently, the presence of cracks due to
cyclic loading was conrmed by using JEOL6360LA scan-
ning electron microscope observations. Each specimen was
characterized by a notable number of cracks with a depth of
< 0.5 mm. The exemplary view of formed cracks was pre-
sented in Fig. 4 for the specimen with 20 μm (a) and 40 μm
(b) thick coating.
3 Results
The resistance measurements of the eddy current probe were
carried out using the Keysight E4980A precision LCR meter
with an accuracy of +/− 0.05%, in the frequency range from
130 kHz to 280 kHz. Eight measurements were performed
for each frequency value, from which the arithmetic mean
was calculated. At the beginning of the experiment, the ref-
erence resistance values RREF were measured for specimens
without defects. In the second step, the resistance R of the
probe placed on specimens subjected to fatigue tests under
stress amplitudes from 300 MPa to 600 MPa was measured.
The probe was moved along the symmetry axis of the sam-
ple with a step of 2 mm, and the nal measurement point
was the one where the largest changes in resistance value
compared to RREF were obtained. The relative resistance dif-
ference δR expressed in [%] was dened according to (1) for
specimen. Subsequently, the pot-core coil was placed in a
head improving the probe’s stability and allowing for the
connection of power supply wires (Fig. 2). One should men-
tion, that broad-band excitation was employed to demon-
strate how the optimal operating frequency of the probe was
selected. Additional aim was to expose, that the sensitivity
of the probe is signicantly reduced at other frequency val-
ues. Once the narrow range of the optimal operating fre-
quency for the probe (165–170 kHz) was established, it was
not necessary to utilize broad-band excitation during the
conducted tests.
Non-destructive measurements were performed on the
specimens’ strain gauge length equal to 52 mm as shown
Fig. 4 Dierent types of cracks formed during fatigue testing in the specimen with 20 μm (a) and 40 μm (b) thick coating
Fig. 3 Engineering drawing of the specimen
Fig. 2 Pot-core probe and specimens of MAR 247 nickel-based super-
alloy with 20 μm and 40 μm thick aluminide coatings
1 3
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Journal of Nondestructive Evaluation (2024) 43:112
sensitivity of the probe can be achieved by using a pot core.
Limiting the leakage of magnetic ux enables satisfac-
tory changes in the resistance of the probe to be obtained.
Additionally, the reactance value of the probe could be also
measured, but changes of around 3% proved insucient to
infer the presence of defects in the specimens. Applying a
probe with a diameter close to the width of the examined
area had two main advantages. Firstly, it reduced the edge
eect compared to a probe with a larger diameter. The sec-
ond advantage was facilitating the precise placement of
the probe relative to the surface being examined so that all
measurement points were located on the sample’s axis of
symmetry.
Preliminary measurements conducted in the frequency
range from 1 kHz to 1 MHz enabled the determination of the
optimal operating frequency value. For low frequencies, the
δR parameter value is relatively small. A signicant change
occurs near the resonant frequency of about 130 kHz. Above
the resonant frequency, there is a sharp increase in the value
of δR, followed by its steady decrease. For such a reason,
the frequency range from 130 kHz to 280 kHz was used
for further research. The δR coecient was assumed as the
highest value for frequencies of 165–170 kHz. Such a nar-
row range of optimal frequency values means that the oper-
ating frequency of the probe only needs to be determined
once. Therefore, a signicant acceleration of the inspection
process could be achieved.
The frequency at which the δR coecient reaches its
maximum value also provides information about the loca-
tion of damage in the specimen structure. The standard
penetration depth for a frequency f = 170 kHz is 0.28 mm,
comparison purposes. The highest value of δR obtained for
the specimen in the entire frequency range from 130 kHz to
280 kHz was marked as δRMAX (Fig. 5).
δR
=
R
REF
−R
RREF
·
100% (1)
The resistance dierence values δR obtained for specimens
with 20 μm coating were presented for column (Fig. 6a), ne
(Fig. 6b), and coarse (Fig. 6c) grain structures. In Fig. 6d,
the resistance dierences were shown for these three-
grain structures when subjected to the stress amplitude of
500 MPa. The highest resistance change values determined
by the parameter δRMAX, obtained for these specimens, are
shown in Fig. 5a. Subsequently, the measurement results for
specimens with 40 μm coatings were presented (Fig. 6e),
and the column, ne, and coarse structures were compared
for a stress amplitude of 500 MPa (Fig. 6f). The values of
the parameter δRMAX are shown in Fig. 5.
4 Discussion
In all measurements conducted using the eddy current
method, the resistance value of the probe signicantly
changed after subjecting the specimens to cyclic loading.
The obtained values of the δR coecient conrmed and
ensured a clear distinction between reference specimens and
those containing structural damage due to fatigue. Achiev-
ing such good results requires the careful selection of the
proper inspection parameters. It was found, that the required
Fig. 5 Maximum values of resistance measured for specimens with 20 μm (a) and 40 μm thick coatings when subjected to stress amplitude equal
to 500 MPa (b)
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Journal of Nondestructive Evaluation (2024) 43:112
Fig. 6 Resistance changes δR registered for specimens with: column
grain structure and coating thickness equal to 20 μm (a); ne grain
structure and coating thickness equal to 20 μm (b) coarse grain struc-
ture and coating thickness equal to 20 μm (c); coating thickness equal
to 20 μm subjected to fatigue testing at stress amplitude of 500 MPa
(d); column grain structure and coating thickness equal to 40 μm (e)
coating thickness equal to 40 μm subjected to fatigue testing at stress
amplitude of 500 MPa (f)
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Journal of Nondestructive Evaluation (2024) 43:112
surface access is limited or the inspection area is complex
[46]. Additionally, ECT can be highly automated and easily
integrated into maintenance routines, providing real-time
data and reducing inspection times. However, the method is
decient when dealing with materials that have thick TBCs,
as the coating can attenuate the eddy currents, reducing the
method’s sensitivity to subsurface defects. Moreover, ECT
is limited in detecting cracks that are oriented parallel to the
surface or those located deeper below the coating, where
the electromagnetic elds are less eective. In such cases,
other non-destructive testing methods, such as ultrasonic
testing or thermography, may be more suitable, as they can
penetrate thicker coatings and detect deeper or dierently
oriented cracks. Overall, while eddy current testing is a
valuable tool for detecting cracks in materials with thermal
barrier coatings, its eectiveness can be compromised by
the thickness of the coating and the orientation and depth of
the defects, necessitating the use of complementary inspec-
tion techniques for comprehensive evaluation.
One should mention, the literature on EC crack detec-
tion in gas turbine blades made of nickel alloys. Further-
more, it is dicult to compare the results, which require
interpretation of the obtained scans, with the numerical
data obtained in the developed methodology presented
in this work. Therefore, some examples of eddy current
application in the assessment of coatings under fatigue or
prolonged service were discussed. Uchanin [47] presented
low-frequency double dierential eddy current probes with
enhanced capability for detecting subsurface cracks were
introduced. These probes come in various sizes, from 5 to
33 mm, and oer dierent spatial resolutions for specic
applications. They operate across a wide frequency range,
from 0.2 kHz to 1.0 MHz, with high penetration depth and
exceptional sensitivity to subsurface defects. The probes are
particularly eective in detecting fatigue cracks in multi-
layer structures, such as riveted aircraft components and
repaired surfaces. This technology enables timely detection
of dangerous damage without needing to disassemble air-
craft or remove protective coatings. Grosso et al. [48] per-
formed conventional eddy current testing (ECT) on samples
consisting of carbon steel substrates coated with anticorro-
sive composites commonly used inside petrochemical stor-
age tanks. Simulated localized corrosion, represented by
undercoating defects, was detected by inspecting the same
side as the machined defects. With defect diameters in the
millimeter range, the results suggest that ECT is capable of
identifying corrosion in its early stages. The accuracy of the
method was unaected by coating thicknesses ranging from
approximately 300 to 1000 μm, as well as the presence of
corrosion products. Additionally, multilevel threshold pro-
cessing enhanced defect detectability by eliminating false
positives, which typically arise from thickness variations
indicating that structural damage is primarily located shal-
low beneath the specimen surface. Based on the obtained
reference resistance values RREF (for f = 130–280 kHz),
there is no possibility to distinguish specimens under inves-
tigation. A dierence in coating thickness of 20 μm is too
small to have a signicant impact on the probe resistance
value. Furthermore, the type of initial microstructure (ne,
coarse, or column) does not signicantly alter the ow of
eddy currents.
The results of the measurements presented in Fig. 6 con-
rmed that the increase in stress amplitude has a signi-
cant inuence on changes in probe resistance caused by the
occurrence of damage. This inuence is more signicant
for lower amplitude values (300–400 MPa) than for higher
ones (500–600 MPa). In all cases, the smallest resistance
changes were obtained for ne grain samples. These val-
ues signicantly diered from those obtained for the other
initial microstructures. The dierences in δR values shown
in Figs. 4 and 5 are caused by the formation of dierent
crack and micropore congurations in samples with dier-
ent initial microstructures, using the same stress amplitude.
Each such crack disrupts the ow of eddy currents, causing
a change in the probe resistance value.
Non-destructive methods for detecting cracks in materi-
als with thermal barrier coatings (TBCs) are essential for
ensuring the reliability and longevity of components, partic-
ularly in high-temperature applications like gas turbines and
aero engines. Among these methods, infrared thermography
is highly eective, leveraging thermal imaging to detect
surface and subsurface cracks by observing thermal con-
trasts caused by dierences in heat ow through the mate-
rial [42]. Another advanced technique is ultrasonic testing,
which uses high-frequency sound waves to detect aws;
in TBCs, this method is particularly useful for identifying
delaminations and vertical cracks that may not be visible on
the surface [43]. Additionally, laser shearography, an optical
method, is eective in identifying surface and near-surface
defects by detecting the deformation response of a material
under stress [44]. X-ray computed tomography (CT) scan-
ning oers detailed internal imaging, capable of detecting
ne cracks and porosity within the coating and substrate,
providing a comprehensive view of material integrity [45].
Each of these methods has its strengths and limitations,
often dictated by the specic characteristics of the TBC, the
type of substrate material, and the nature of the cracks; thus,
a combination of techniques is often employed to achieve
the most accurate assessment of crack presence and propa-
gation in materials with thermal barrier coatings. In compar-
ison to these methods, the eddy current method is superior
in its sensitivity to small cracks and its ability to provide
rapid and localized assessments, which makes it particularly
eective for early-stage detection and in situations where
1 3
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Journal of Nondestructive Evaluation (2024) 43:112
5 Conclusion
The conducted research using the eddy current method
has demonstrated its eectiveness in detecting structural
damage due to fatigue by measuring changes in probe
resistance. Signicant dierences in the δR coecient
distinguished damaged specimens from references, dem-
onstrating the method’s sensitivity. Optimal measurement
accuracy was achieved by using a pot core, selecting appro-
priate probe diameters, and operating at frequencies around
165–170 kHz, where the δR coecient was highest. The
sensitivity was more noticeable at lower stress amplitudes
and varied with initial microstructures, although ne grain
samples showed minimal resistance changes. The study
highlights the importance of optimizing inspection param-
eters to improve the reliability of the eddy current method in
detecting material damage.
Acknowledgements The authors would like to express their gratitude
to Mr M. Wyszkowski and Prof. D. Kukla for their kind help during the
experimental part of this work.
Author Contributions G. T.: Conceptualization, Data curation, Formal
analysis, Investigation, Methodology, Project administration, Supervi-
sion, Validation, Visualization, Roles/Writing - original draft, Writing
- review & editing. M. A.-H.: Data curation, Investigation, Validation.
Y. L.: Formal analysis, Methodology. M. K.: Conceptualization, Data
curation, Formal analysis, Investigation, Methodology, Project admin-
istration, Supervision, Validation, Visualization, Roles/Writing - origi-
nal draft, Writing - review & editing.
Data Availability No datasets were generated or analysed during the
current study.
Declarations
Competing Interests The authors declare no competing interests.
Open Access This article is licensed under a Creative Commons
Attribution 4.0 International License, which permits use, sharing,
adaptation, distribution and reproduction in any medium or format,
as long as you give appropriate credit to the original author(s) and the
source, provide a link to the Creative Commons licence, and indicate
if changes were made. The images or other third party material in this
article are included in the article’s Creative Commons licence, unless
indicated otherwise in a credit line to the material. If material is not
included in the article’s Creative Commons licence and your intended
use is not permitted by statutory regulation or exceeds the permitted
use, you will need to obtain permission directly from the copyright
holder. To view a copy of this licence, visit http://creativecommons.
org/licenses/by/4.0/.
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through non-destructive testing. Das et al. [51] reported
frequency scanning eddy current testing (F-SECT) for
condition assessment of multiple layers of coating on gas
turbine blades. It was proven, that such technique can be
used to evaluate the condition of MCrAlY coatings on gas
turbine blades and vanes. It serves as a quality control tool
for inspecting both new and refurbished blades, as well as
optimizing refurbishment intervals. This method is particu-
larly relevant for gas turbine units operating under partial
loading, where refurbishment may not be required based
solely on operating hours. FSECT is anticipated to reduce
unnecessary maintenance and lower the life cycle costs of
coated blades and vanes.
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Journal of Nondestructive Evaluation (2024) 43:112
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