ISO 24449:2021

Metallic and other inorganic coatings - Determination of thermal conductivity of thermal barrier coatings at elevated temperature

This document specifies a method for determining the thermal conductivity of ceramic top coat (TC) constituting thermal barrier coating (TBC) subjected to heat treatment, in a direction normal to the coating surface, from room temperature up to 1 000 °C.

Revêtements métalliques et autres revêtements inorganiques — Détermination de la conductivité thermique des revêtements barrières thermiques à température élevée

General Information

• Status: Published
• Publication Date: 26-Oct-2021
• ICS: 25.220.20 - Surface treatment
• Technical Committee: ISO/TC 107 - Metallic and other inorganic coatings
• Drafting Committee: ISO/TC 107/WG 1 - Thermal spraying
• Current Stage: 6060 - International Standard published
• Start Date: 27-Oct-2021
• Due Date: 30-Sep-2022
• Completion Date: 27-Oct-2021

Overview

ISO 24449:2021 specifies a standardized method to determine the thermal conductivity of the ceramic top coat (TC) of thermal barrier coatings (TBCs) in the direction normal to the coating surface, from room temperature up to 1 000 °C. The method uses flash-type thermal diffusivity measurements on heat-treated specimens and calculates TC thermal conductivity from measured thermal diffusivity, specific heat capacity and bulk density using a multi‑layer analytical model.

Key topics and technical requirements

• Scope: Measurement of thermal conductivity for ceramic top coats (TC) in TBC systems (substrate + bond coat + top coat) at elevated temperatures up to 1 000 °C.
• Specimen types and preparation: Uses two specimen types - substrate alone and TBC (substrate+bond coat+TC). Specimens are flat disks or square plates with lateral dimensions in the range given by the standard (typical diameters/side lengths ≈ 10–15 mm). The standard defines thickness ranges (substrate and total TBC) and thickness tolerances and requires controlled polishing and surface treatment.
• Heat treatment: TBC specimens are heat-treated at the maximum specified test temperature for 2–3 hours prior to measurement to stabilize microstructure.
• Measurement principle: Thermal diffusivity is measured by the flash (pulse) method (see ISO 18755), recording temperature‑rise curves on the rear/coating surface with an infrared radiometer following a pulse heating light source. Both substrate and TBC temperature‑rise curves are measured at each test temperature.
• Data and calculations: Thermal diffusivity of the TC is derived using a multi‑layer analytical model (areal heat diffusion time method or theoretical temperature‑rise curve method) combined with separately measured specific heat capacity and bulk density to compute thermal conductivity.
• Specimen surface treatment: Both faces are coated with a thin opaque black layer (e.g., colloidal graphite or sputtered metal + graphite) to ensure high absorption and emissivity. Polishing with abrasive paper P800 or finer is specified for TC surface finish.

Applications and users

• Who uses it: Coating manufacturers, materials testing laboratories, R&D groups, turbine OEMs, quality assurance teams and failure-analysis engineers.
• Practical uses: Characterizing high‑temperature insulating performance of TBCs for gas turbine blades, vanes, combustors and aero‑engine hot‑section components; validating coating process changes; comparing TBC materials and architectures; supporting lifetime and thermal modeling studies.

Related standards

• ISO 18755 - thermal diffusivity by laser/flash method
• ISO 18555 - thermal conductivity of TBCs at room temperature
• ISO 1463 - coating thickness (microscopical)
• ISO 14188 - TBC thermal cycle and shock tests
• EN 821‑3 - specific heat capacity for ceramics

Keywords: ISO 24449:2021, thermal barrier coatings, thermal conductivity measurement, thermal diffusivity, flash method, high‑temperature testing, ceramic top coat, TBC testing.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 24449
First edition
2021-10
Metallic and other inorganic
coatings — Determination of thermal
conductivity of thermal barrier
coatings at elevated temperature
Revêtements métalliques et autres revêtements inorganiques —
Détermination de la conductivité thermique des revêtements
barrières thermiques à température élevée
Reference number
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Apparatus for measuring thermal diffusivity . 3
6 Specimen . 3
6.1 Shape and dimensions . 3
6.2 Specimen preparation . 5
7 Measuring procedure . 5
7.1 Specimen thickness . 5
7.2 Thermal diffusivity . 6
7.2.1 Measurement of temperature-rise curve . 6
7.2.2 Calculation of thermal diffusivity of substrate . 6
7.2.3 Calculation of thermal diffusivity of TC . 6
7.3 Specific heat capacity . 7
7.4 Bulk density . 7
8 Thermal conductivity of TC . 8
9 Report . 8
Bibliography .10
iii
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
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 107, Metallic and other inorganic coatings.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
Thermal barrier coatings are highly advanced material systems, generally applied to surfaces of hot-
section components made of nickel or cobalt-based superalloys, such as combustors, blades, and vanes
of power-generation gas turbines in thermal power plants and aero-engines 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 that 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 an important property of thermal barrier coatings, ISO 18555 only
describes a method for measuring this parameter of thermal barrier coatings at room temperature.
v
INTERNATIONAL STANDARD ISO 24449:2021(E)
Metallic and other inorganic coatings — Determination
of thermal conductivity of thermal barrier coatings at
elevated temperature
1 Scope
This document specifies a method for determining the thermal conductivity of ceramic top coat (TC)
constituting thermal barrier coating (TBC) subjected to heat treatment, in a direction normal to the
coating surface, from room temperature up to 1 000 °C.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. 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 14188, Metallic and other inorganic coatings — Test methods for measuring thermal cycle resistance
and thermal shock resistance for thermal barrier coatings
ISO 18555, Metallic and other inorganic coatings — Determination of thermal conductivity of thermal
barrier coatings
ISO 18755, Fine ceramics (advanced ceramics, advanced technical ceramics) — Determination of thermal
diffusivity of monolithic ceramics by laser flash method
EN 821-3, Advanced technical ceramics – Monolithic ceramics. Thermophysical properties – Part 3:
Determination of specific heat capacity
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 14188, ISO 18555 and the
following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
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 of a heat-resistant
metallic material
Note 1 to entry: See Figure 1.
Key
1 top coat (TC) 3 substrate
2 bond coat (BC) 4 thermal barrier coating
Figure 1 — Diagrammatic view of a section of a TBC
4 Principle
The TBC specimen shall be heat-treated prior to the measurement at elevated temperature in order
to minimize the change of the coating microstructure. Since the heat-treated BC specimen consisting
of the substrate and the BC can be treated as the same as the substrate specimen, the TBC specimen
can be regarded as a two-layer model consisting of the substrate and the TC. Thermal conductivities
of the substrate and TC are determined in accordance with calculation using the thermal diffusivities,
[1]
specific heat capacities, and bulk densities . The fundamental procedures are shown in Figure 2.
The fundamental procedures for de
...