ISO 21465:2025

International
Standard
ISO 21465
First edition
Test method for CMAS corrosion
2025-03
of thermal/environmental
barrier coatings under dynamic
thermal cycling
Méthode d'essai de la corrosion par les CMAS des systèmes
barrières thermiques/environnementales dans le cadre d'un
cyclage thermique dynamique
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Test methods . 3
5.1 CMAS corrosion under dynamic thermal cycling without thermal gradient .3
5.1.1 CMAS composition .3
5.1.2 CMAS coating .3
5.1.3 Test method .3
5.1.4 Detection of the accurate temperature .3
5.1.5 Determination of failed samples .3
5.1.6 Apparatus .4
5.2 CMAS corrosion under dynamic thermal cycling with thermal gradient.4
5.2.1 CMAS suspension and CMAS precursor solution .4
5.2.2 CMAS concentrations .4
5.2.3 CMAS injection rate .4
5.2.4 Test method .4
5.2.5 Heating temperature and time .5
5.2.6 Determination of failed samples .5
5.2.7 Equipment design .5
6 Test report . 6
Annex A (informative) CMAS corrosion under dynamic thermal cycling without thermal
gradient. 7
Bibliography . 8

iii
Foreword
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iv
Introduction
This document provides the test method for calcia–magnesia–aluminosilicate (CMAS) corrosion of thermal/
environmental barrier coatings (T/EBCs) under dynamic thermal cycling. The CMAS corrosion behaviour
affects the performance and service life of the T/EBCs. The multi-layer structure of the T/EBC is deposited on
Ni-superalloys/SiC-based ceramic substrates using different methods such as atmospheric plasma spraying
(APS), plasma spray-physical vapour deposition (PS-PVD), electron beam physical vapour deposition (EB-
PVD), high-velocity oxygen fuel (HVOF). Therefore, the deposition methods and thickness of T/EBCs should
meet the requirements of service conditions.
CMAS can be in the form of airborne sand, runway debris or volcanic ash in aircraft engines and ambient dust
or fly ash in power generation engines. Gas turbine engines are attacked by the CMAS when the aerospace
spacecraft or aircraft flies above desert and volcanic areas. The diffusion, reaction and viscosity of the molten
CMAS can cause serious corrosion of T/EBC, resulting in the T/EBC's spallation and failure. Consequently,
the operation lifetime of the gas turbine is reduced. Therefore, the behaviour of CMAS corrosion of T/EBCs
is an important assessment index of T/EBCs performance. A unified international test standard is required
to evaluate CMAS corrosion of thermal/environmental barrier coatings (T/EBCs) under dynamic thermal
cycling. This document aims to formulate a standardized and unified test method, including the process and
the failure determination criteria, for the performance of T/EBCs.

v
International Standard ISO 21465:2025(en)
Test method for CMAS corrosion of thermal/environmental
barrier coatings under dynamic thermal cycling
1 Scope
This document specifies requirements for the test method of the CMAS corrosion of thermal/environmental
barrier coatings under dynamic thermal cycling, including the process and the determination of failure after
corrosion.
The document does not apply to such coatings on plastics to be used for aerospace, electronics and other
engineering fields.
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 13123, Metallic and other inorganic coatings — Test method of cyclic heating for thermal-barrier coatings
under temperature gradient
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
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13123, ISO 14188, and 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/environmental barrier coating
T/EBC
protective coating on the superalloy or SiC-based substrate to reduce the heat transfer from the outside
topcoat layer through the coating to the substrate
Note 1 to entry: T/EBC inhibits the oxidation of the substrate, increases the operation temperature and improves
the service life of the substrate when exposed to harsh environments, such as air, water vapour and molten calcia-
magnesia-aluminosilicate (3.2) conditions. Generally, a bond coat layer is placed between the T/EBC and substrate to
mitigate the coefficient of thermal expansion incompatibilities. Figure 1 shows the schematic diagram of the T/EBC on
the substrate. The T/EBC is sprayed on the bond coat layer using APS, PS-PVD, EB-PVD, HVOF, etc.

Key
1 thermal/environmental barrier coating (T/EBC)
2 thermally grown oxide (TGO)
3 bond coat (BC)
4 substrate
Figure 1 — Diagrammatic representation of a section of T/EBC
3.2
calcia–magnesia–aluminosilicate
CMAS
mixture consisting of CaO, MgO, Al O and SiO
2 3 2
Note 1 to entry: CMAS can be in the form of airborne sand, runway debris or volcanic ash in aircraft engines and
ambient dust or fly ash in power generation engines.
3.3
dynamic thermal cycling
system comprising the heating, holding and cooling process
3.4
ratio of spalling area
proportion of the total spalling area relative to the effective area of the thermal/environmental barrier
coating (T/EBC) (3.1), which is used to determine the failure of the T/EBC
4 Principle
The CMAS powder is coated on the surface of the T/EBCs, or a CMAS suspension is injected into a suitable
flame and spread on the surface of the T/EBCs. One dynamic thermal cycle comprises the heating, holding
and cooling processes. After cooling to room temperature using compressed air, the ratio of spalling areas is
calculated to determine the failure of T/EBCs due to CMAS corrosion.

5 Test methods
5.1 CMAS corrosion under dynamic thermal cycling without thermal gradient
5.1.1 CMAS composition
The basic constituents of CMAS powder are CaO, MgO, Al O and SiO . The composition of CMAS is uncertain
2 3 2
and depends on different geographical locations. The compositions for the test shall be 22CaO-19MgO-7Al O -
2 3
45SiO or 33CaO–9MgO–13AlO –45SiO ; however, the CMAS composition can also be adjusted through
2 1.5 2
simulation, considering the natural variations in CMAS compositions
...