ISO 20267:2017

INTERNATIONAL ISO
STANDARD 20267
First edition
2017-05
Thermal spraying — Determination
of interfacial toughness of ceramic
coatings by indentation
Projection thermique — Détermination de la ténacité interfaciale des
revêtements céramiques par indentation
Reference number
ISO 20267:2017(E)
©
ISO 2017

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ISO 20267:2017(E)

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ii © ISO 2017 – All rights reserved

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ISO 20267:2017(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and units . 1
5 Principle . 3
6 Test pieces and sample preparation . 3
6.1 Thicknesses of coating and substrate . 4
6.2 Sample size . 4
6.3 Sample cutting . 4
6.4 Mounting . 4
6.5 Surface polishing . 4
7 Apparatus . 5
8 Procedure and conditions of testing . 5
8.1 Indentation . 5
8.2 Indentation and crack length measurement . 5
9 Evaluation of indentation interfacial toughness . 7
9.1 Analysis. 7
9.2 Test validity . 7
10 Test report . 8
10.1 Items to be reported . 8
10.2 Other items to be reported . 9
Bibliography .10
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ISO 20267:2017(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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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
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This document was prepared by Technical Committee ISO/TC 107, Metallic and other inorganic coatings.
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ISO 20267:2017(E)

Introduction
The interfacial toughness of thermal spray ceramic coatings is required for two reasons:
a) to understand quantitatively degradation of adhesion in service;
b) for life assessment of the coated components.
Adhesion strength of thermal spray coatings is usually measured in accordance with the tensile
method specified by ISO 14916. However, there is a technical limitation in the application of ISO 14916.
It requires preparation of a tensile adhesion test specimen using glue and, as such, coatings with
higher adhesion strength than glue cannot be quantitatively evaluated. By virtue of its simplicity and
practicality, an indentation method is a promising method to evaluate the adhesion of such coatings. In
this method, a Vickers hardness tester is used. An interfacial toughness value is evaluated by measuring
a length of the crack formed after pushing the indenter on the coating interface. The application of the
method specified in this document can reduce uncertainty over the adhesion strength evaluation of
coatings and makes it possible to evaluate the adhesion strength in a simpler way.
-3/2
The results can be expressed either as a stress intensity factor, in MN∙m , or as a fracture surface
-2
energy, in J∙m .
“Interfacial toughness” can have several meanings.
-3/2
a) Interfacial fracture toughness, K , in MN∙m , is a material constant that shows how easily the
Ic
coating may be peeled away from a substrate.
b) Energy release rate (or work done to fracture), G, is an alternative expression for interfacial fracture
2 2
toughness, often obtained by converting K to G [i.e. G = K (1 - ν )/E, where E is Young’s modulus and
-2
ν is Poisson’s ratio]. G has units of J∙m .
For the purposes of developing the test method, the term indentation interfacial toughness, K , is
IFC
defined separately from interfacial fracture toughness, K . The indentation interfacial toughness is
Ic
a value obtained by using Vickers hardness tester, and is calculated from the total length of cracks
induced along the interface by the indentation. Shorter crack lengths indicate that the coating has
higher interfacial toughness or adhesion strength than other samples with longer cracks. There is no
standard method to determine such interfacial toughness for thermal spray ceramic coatings, and
different organizations or groups currently use their own evaluation procedures.
When measurements are carefully performed following the methods defined in this document,
the evaluation of crack length, and thus interfacial toughness, will not require much effort and can
describe the adhesion characteristics of the system (substrate chemistry, pre-preparation/roughness
of substrate surface, coating chemistry and properties). This document recommends good practice to
minimize uncertainty in the measurement procedures.
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INTERNATIONAL STANDARD ISO 20267:2017(E)
Thermal spraying — Determination of interfacial
toughness of ceramic coatings by indentation
1 Scope
This document specifies a method for measuring the interfacial toughness of thermal spray ceramic
coatings at room temperature based on an indentation method. The interfacial toughness is calculated
from the mean length of cracks emanating from the corners of the impression induced by a Vickers
hardness tester, and it is intended for use with ceramic coatings with a single layer or multilayers. The
test procedures proposed in this document are intended for use in an ambient environment.
This document is recommended for thermal spray ceramic coatings such as thermal barrier coatings,
wear resistant coatings and electrical insulating coatings.
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 6507-1, Metallic materials — Vickers hardness test — Part 1: Test method
ISO 6507-2, Metallic materials — Vickers hardness test — Part 2: Verification and calibration of testing
machines
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at http:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Symbols and units
For the purposes of this document, the symbols and units given in Table 1 apply (see also Figures 1 and 2).
Table 1 — Symbols and designations
Symbol Designation Unit
a diagonal half-length of impression parallel to interface m
c mean value of half crack length: (c + c )/2 m
1 2
c , c individual crack lengths at corner of impression (lengths from crack tip to centre of m
1 2
impression, parallel with the macroscopic interface)
−2
E Young’s modulus of ceramic coating GN·m
1
−2
E Young’s
...