ISO 18555:2016

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 18555
ISO/TC 107
Metallic and other inorganic
Secretariat: KATS
coatings — Determination of thermal
Voting begins
on: 2015­10-16 conductivity of thermal barrier
coatings
Voting terminates
on: 2015-12-16
Revêtements métalliques et autres revêtements inorganiques —
Détermination de la conductivité thermique des revêtements
barrières thermiques
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 18555:2015(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
©
NATIONAL REGULATIONS. ISO 2015

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ISO/FDIS 18555:2015(E)

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ii © ISO 2015 – All rights reserved

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ISO/FDIS 18555:2015(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 4
5 Apparatus for measuring thermal diffusivity . 4
6 Specimen . 5
6.1 Shape and dimensions . 5
6.2 Surface treatment . 7
7 Measuring procedure . 7
7.1 Specimen thickness . 7
7.2 Thermal diffusivity . 7
7.2.1 Measurement of temperature­rise curve . 7
7.2.2 Calculation of thermal diffusivity of substrate . 7
7.2.3 Calculation of thermal diffusivities of BC and TC . 7
7.3 Specific heat capacity .10
7.4 Bulk density .10
8 Thermal conductivities of BC and TC .11
9 Report .11
9.1 Items to be reported .11
9.2 Additional items to be selected for the report .12
Annex A (informative) Areal heat diffusion time method .13
Annex B (informative) Examples of theoretical temperature-rise curves .16
Bibliography .18
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ISO/FDIS 18555:2015(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
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Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
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The committee responsible for this document is ISO/TC 107, Metallic and other inorganic coatings.
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ISO/FDIS 18555:2015(E)

Introduction
Thermal barrier coatings are highly advanced material systems. They are generally applied to surfaces
of hot-section components made of nickel or to cobalt-based superalloys, such as combustors, blades,
vanes of power­generation gas turbines in thermal power plants and aero­engines operated at elevated
temperatures.
The function of these coatings is to protect metallic components for extended periods at elevated
temperatures by employing thermally insulating materials which can sustain an appreciable
temperature difference between load bearing alloys and coating surfaces. These coatings permit the
high-temperature operation by shielding these components, thereby extending their lives.
Although thermal conductivity is one of the most important properties of thermal barrier coatings,
the existing ISO standard (ISO 18755:2005) includes only the method for determining the thermal
diffusivity of monolithic ceramics, regarding the heat conduction in thermal barrier coating.
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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 18555:2015(E)
Metallic and other inorganic coatings — Determination of
thermal conductivity of thermal barrier coatings
1 Scope
This International Standard specifies the method for determining the thermal conductivities of thermal
barrier coatings consisting of metallic bond coats and ceramic top coats, in a direction normal to the
coating surface, at room temperature.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 1463, Metallic and oxide coatings — Measurement of coating thickness — Microscopical method
ISO 18755:2005, Fine ceramics (advanced ceramics, advanced technical ceramics) — Determination of
thermal diffusivity of monolithic ceramics by laser flash method
EN 821­3, Advanced technical ceramics — Monolithic ceramics. Thermophysical properties — Part 3:
Determination of specific heat capacity
ASTM E1269­11, Standard Test Method for Determining Specific Heat Capacity by Differential Scanning
Calorimetry
3 Terms and definitions
For the purpose of this standard, the terms and definitions given in ISO 18755:2005 and the
following apply.
3.1
thermal barrier coating
TBC
two-layer coating consisting of a metallic bond coat (BC) and a ceramic top coat (TC), in order to reduce
heat transfer from outside of the top coat through the coating to the substrate
Note 1 to entry: See Figure 1.
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ISO/FDIS 18555:2015(E)

Key
1 top coat (TC)
2 bond coat (BC)
3 substrate
4 thermal barrier coating (TBC)
Figure 1 — Diagrammatic view of a section of TBC
[SOURCE: ISO 14188:2012, definition 3.1, modified]
3.2
apparent thermal diffusivity
thermal diffusivity of the specimens [substrate with bond coat (BC) and substrate with thermal barrier
coating (TBC)] in a direction normal to the coating surface
3.3
normalized temperature rise
T(t)/ΔT
value which is determined by dividing the difference between the temperature of the specimen rear
surface after the pulse heating and the temperature of the specimen rear surface before the pulse
heating by the difference between the maximum temperature of the specimen rear surface and the
temperature of the specimen rear surface before the pulse heating
Tt() Tt()−T
10
=
ΔT TT−
max 0
where
T (t) is temperature of specimen rear surface after pulse heating by a flash method;
1
t is time;
T is temperature of the specimen rear surface before pulse heating;
0
T is maximum temperature of specimen rear surface.
max
Note 1 to entry: See Figure 2.
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ISO/FDIS 18555:2015(E)

a) Flash method b) Temperature-rise curve under ideal conditions
Key
1 pulse heating X time (s)
2 specimen Y normalized temperature rise T(t) / ΔT
3 substrate A areal heat diffusion time (s)
4 TBC
5 front surface
6 rear surface
7 infrared radiometer
Figure 2 — Flash method and temperature-rise curve under ideal conditions
3.4
temperature-rise curve
curve which shows the variation in the normalized temperature rise of the specimen rear surface with
time
Note 1 to entry: See the thick solid line in Figure 2b.
3.5
half rise-time
t
1/2
time required for the normalized temperature rise to reach 0,5 in the temperature­rise curve
Note 1 to entry: See Figure 2b.
3.6
areal heat diffusion time
A
area with time-dimension which is bordered by the horizontal line at the height of the maximum
temperature-rise and by the temperature-rise curve
Note 1 to entry: See Figure 2b.
3.7
heat diffusion time
τ
0
time period beginning with pulse heating of the specimen front surface until time at which the specimen
temperature becomes uniform
2
d
τ =
0
α
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ISO/FDIS 18555:2015(E)

where
τ is heat diffusion time (s);
0
d is thickness of specimen (m);
2
α is thermal diffusivity (m /s).
Note 1 to entry: See Figure 2b.
4 Principle
Thermal conductivities of the substrate, BC, and TC are determined according to calculations using
the thermal diffusivities, specific heat capacities and bulk densities. The fundamental procedures are
shown in Figure 3.
The fundamental procedures for determining the thermal diffusivities of the substrate, BC, and TC
consist of the measurement of temperature-rise curves of three types of specimens (substrate, substrate
with BC, and substrate with TBC) by a flash method, and of calculations. The thermal diffusivities of the
BC and TC are obtained by applying a multi-layer analytical model to the temperature-rise curves.
The specific heat capacities and bulk densities of the substrate, BC, and TC are measured separately.
Figure 3 — Fundamental procedures for determining thermal conductivity
5 Apparatus for measuring thermal diffusivity
An example of the apparatus for measuring the thermal diffusivity is schematically shown in Figure 4.
The apparatus consists of the following.
5.1 Pulse heating light source.
5.2 Data recorder.
5.3 Measurement circuit.
5.4 Infrared radiometer.
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ISO/FDIS 18555:2015(E)

5.5 Specimen holder.
5.6 Chamber.
5.7 Thermocouple.
5.8 Temperature indicator.
The apparatus shall be specified according to ISO 18755:2005 and should be calibrated using reference
data and reference materials in reference to Annex E in ISO 18755:2005.
Key
1 pulse heating light source 7 temperature signal of specimen rear surface
2 data recorder 8 specimen
3 measurement circuit 9 specimen holder
4 infrared radiometer 10 chamber
5 trigger signal 11 thermocouple
6 amplification of signal 12 temperature indicator
Figure 4 — Typical apparatus for measuring the thermal diffusivity according to a flash method
6 Specimen
6.1 Shape and dimensions
The shape and dimensions of the specimen shall be as follows.
a) The three types of specimens (the substrate, BC and TBC specimens) shall be used.
b) The specimen shape shall be a flat disk (Figure 5) or flat square plate (Figure 6). The diameter or
−3 −3
side length of the specimen shall be from 10 × 10 m to 15 × 10 m.
c) The thicknesses of the substrate, BC and TC are given in Table 1.
d) The substrate thickness shall be the same for the three types of specimens.
−3
e) The thickness tolerance of substrate shall be ± 0,01 × 10 m.
f) The thickness of BC shall be the same for the BC and TBC specimens.
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ISO/FDIS 18555:2015(E)

g) The difference between maximum and minimum thickness shall be ≤ 0,01 d for the TBC specimen.
h) The coating surface should be polished mechanically in order to smooth the coating surface for the
BC and TBC specimens.
i) The selections of the shape, the dimension and the thickness shall be decided according to the
agreement between parties involved in the transaction.
j) For measurement of the specific heat capacities of BC and TC, the coatings stripped off the
substrates shall be used as the specimen.
a) Substrate specimen b) BC specimen c) TBC specimen
Key
1 substrate
2 bond coat
3 top coat
D diameter
d thickness of substrate
S
d
thickness of bond coat
BC
d thickness of top coat
TC
Figure 5 — Shape of flat disk specimens
a) Substrate specimen b) BC specimen c) TBC specimen
Key
1 substrate
2 bond coat
3 top coat
l side length
d thickness of substrate
S
d thickness of bond coat
BC
d thickness of top co
...