CEN/TS 1071-9:2004

SLOVENSKI STANDARD
01-januar-2005
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Advanced technical ceramics - Methods of test for ceramic coatings - Part 9:
Determination of fracture strain
Hochleistungskeramik - Verfahren zur Prüfung keramischer Schichten - Teil 9:
Bestimmung der Bruchdehnung
Céramiques techniques avancées - Méthodes d'essai pour revetements céramiques -
Partie 9: Détermination de la déformation a la rupture
Ta slovenski standard je istoveten z: CEN/TS 1071-9:2004
ICS:
25.220.99 Druge obdelave in prevleke Other treatments and
coatings
81.060.30 Sodobna keramika Advanced ceramics
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

TECHNICAL SPECIFICATION
CEN/TS 1071-9
SPÉCIFICATION TECHNIQUE
TECHNISCHE SPEZIFIKATION
February 2004
ICS 17.040.20; 25.220.99; 81.060.30
English version
Advanced technical ceramics – Methods of test for ceramic
coatings – Part 9: Determination of fracture strain
Céramiques techniques avancées – Méthodes d’essai pour Hochleistungskeramik – Verfahren zur Prüfung
revêtements céramiques – Partie 9: Détermination de la keramischer Schichten – Teil 9: Bestimmung der
contrainte à la rupture Bruchdehnung
This Technical Specification (CEN/TS) was approved by CEN on 28 December 2003 for provisional application.
The period of validity of this CEN/TS is limited initially to three years. After two years the members of CEN will be requested to submit their
comments, particularly on the question whether the CEN/TS can be converted into a European Standard.
CEN members are required to announce the existence of this CEN/TS in the same way as for an EN and to make the CEN/TS available. It
is permissible to keep conflicting national standards in force (in parallel to the CEN/TS) until the final decision about the possible
conversion of the CEN/TS into an EN is reached.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United
Kingdom.
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EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2004 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TS 1071-9:2004 E
worldwide for CEN national Members.

Contents Page
Foreword. 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions. 5
4 Significance and use . 6
5 Principle. 6
6 Apparatus and materials. 6
6.1 Instrumentation. 6
6.2 Specimen preparation . 7
7 Test procedure . 8
7.1 Calibration . 8
7.2 Sample loading. 8
7.3 Strain determination . 8
7.4 Crack detection . 9
7.5 Test parameters . 9
8 Reporting of results. 10
Bibliography . 15
Foreword
This Technical Specification (CEN/TS 1071-9:2004) has been prepared by Technical Committee CEN/TC 184
“Advanced technical ceramics”, the secretariat of which is held by BSI.
EN 1071 Advanced technical ceramics — Methods of test for ceramic coatings consists of 11 parts:
Part 1: Determination of coating thickness by contact probe profilometer
Part 2: Determination of coating thickness by the crater grinding method
Part 3: Determination of adhesion and other mechanical failure modes by a scratch test
Part 4: Determination of chemical composition
Part 5: Determination of porosity
Part 6: Determination of the abrasion resistance of coatings by a micro-abrasion wear test
Part 7: Determination of hardness and Young's modulus by instrumented indentation testing
1)
Part 8: Rockwell indentation test for evaluation of adhesion
Part 9: Determination of fracture strain
1)
Part 10: Determination of coating thickness by cross sectioning
1)
Part 11: Measurement of internal stress with the Stoney formula
Parts 7 to 11 are Technical Specifications.
This Technical Specification includes a bibliography.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to announce this Technical Specification: Austria, Belgium, Cyprus, Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland
and the United Kingdom.
1) In preparation at the time of publication of this Technical Specification.
Introduction
The fracture strain of a coating is a critical factor often determining the performance of a coated product.
Clearly if stressed either directly or due to thermal effects (thermal expansion coefficient mismatch between
the coating and substrate) coating cracking can occur if the critical fracture stress/strain is exceeded, and in
many cases the effectiveness of the coating will be reduced. For example, corrosion resistant coatings loose
their protective character if cracking occurs, and optical coatings become ineffective when cracked. In many
cases cracking is the first stage of a much more serious form of failure in which large areas of the coating can
spall.
The extent to which coated components can withstand external applied loads is an important property in the
application of any coated system, and usually the failure stress is required. For calculation of the stress both
the fracture strain and Young’s modulus of the coating should be known. CEN/TS 1071-7 can be used to
measure the Young’s modulus by depth sensing indentation, but there are other methods involving flexure
and impact excitation that may also be applied [1], [2]
1 Scope
This part of EN 1071 describes a method of measuring the fracture strain of ceramic coatings by means of
uniaxial tension or compression tests coupled with acoustic emission to monitor the onset of cracking of the
coating. Tensile or compressive strains can also be applied by flexure using four-point bending.
Measurements can be made in favourable cases at elevated temperatures as well as at room temperature.
2 Normative references
This Technical Specification incorporates by dated or undated reference, provisions from other publications.
These normative references are cited at the appropriate places in the text, and the publications are listed
hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to
this Technical Specification only when incorporated in it by amendment or revision. For undated references
the latest edition of the publication referred to applies (including amendments).
EN 10002-1, Metallic materials - Tensile testing – Part 1: Method of test at ambient temperature
EN 10002-5, Metallic materials - Tensile testing – Part 5: Method of testing at elevated temperature
ISO 12106, Metallic materials - Fatigue testing - Axial-strain-controlled method
3 Terms and definitions
For the purposes of this Technical Specification, the following terms and definitions apply.
3.1
fracture strain
strain required to create a detectable crack in the coating
NOTE The presence of the crack can be detected using optical or scanning electron microscopy, or indirectly using
acoustic emission signals
3.2
acoustic emission (AE)
generation of acoustic signals; these signals are recorded as hits, counts, energy or amplitude
NOTE See Figure 1 for definition of AE signals.
3.3
AE hit
single acoustic event above a set threshold
3.4
AE energy
area of the waveform of an AE hit
3.5
AE amplitude
peak of the waveform of an AE hit
3.6
AE counts
number of times the AE waveform passes a set threshold within a single hit
3.7
AE threshold
arbitrary AE amplitude at which AE hits are deemed to be significant and above the AE signals generated by
the test equipment
3.8
waveguide
metallic wire connecting (usually by spot welding) the sample to the AE transducer
4 Significance and use
This test procedure covers the measurement of fracture strain in tension or compression in coatings subject to
mechanical stress at ambient or elevated temperature.
The method is applicable to cases where the substrate is sufficiently ductile such that fracture of the coating
occurs before the substrate. In addition, if during plastic deformation of the substrate acoustic signals are
generated, this may interfere with those caused by coating fracture. Where possible it is recommended that a
test be carried out with the uncoated substrate to determine whether such extraneous AE signals occur.
5 Principle
Specimens of appropriate geometry are submitted to a mechanical stress; the subsequent strain is measured
and the onset of coating failure is detected. The test draws upon the expertise of standard tensile and
compressive tests but requires additional care due to the precision required of the measurements. The
applied stress may be tensile or compressive and may be applied directly or in flexure. The test shall be
carried out to satisfy the requirements of accepted standards for mechanical testing of materials under the
selected method of loading.
NOTE 1 Detection of the fracture of coatings can be carried in a number of ways. The most convenient is to use
acoustic emission (AE), which allows continuous monitoring of the specimen. Acoustic signals are produced when a crack
forms. These signals are captured using suitable detectors and the signals generated are then analysed. In many cases
a waveguide is used to carry the signal from the specimen to the detector; this waveguide is normally a metallic material.
Use of two AE detectors can help to eliminate extraneous signals coming from the loading mechanism. Commercially
available AE systems can be used for this work.
NOTE 2 Where AE cannot be used, crack detection is possible by high resolution video systems, which may allow
continuous monitoring. Alternatively, optical or scanning electron microscopy can be used to examine the samples.
Normally this is done post-test, but in situ examination is also possible.
6 Apparatus and materials
6.1 Instrumentation
6.1.1 In simplest terms the equipment required is a mechanism to apply load to the specimen;
extensometry to measure the strain; and apparatus to detect/monitor fracture of the surface layer. Load is
normally applied continuously through servo-electric testing machines; the load capacity of the frame should
be sufficient to allow straining of the specimen to beyond the yield point of the substrate material.
Continuation of the test to complete separation of the specimen is not normally required.
6.1.2 For flexural testing a suitable test jig is required – four-point bending is recommended as this applies
more uniform bending moment over the gauge length. A suitable jig is shown in Figure 2.
6.1.3 Extensometry should be sufficiently precise to measure strain at a resolution of 0,01%.
6.1.4 For tests at high temperatures using the uniaxial test configuration a furnace is required which allows
access for attachment of load frame, extensometry, thermocouples and waveguides to transmit the AE signals
to the AE detector(s). For the four-point bend configuration, an oxidation resistant jig shall be used.
NOTE Deformation of oxide layers formed on a metallic jig will probably contribute to AE signals during the test.
6.1.5 Crack detection in the coating may be performed visually or by monitoring AE. Visual inspection
requires suitable long focal length video facilities with a field of view containing the gauge length. At high
temperatures the availability of a cool path to
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