CEN/TS 1071-7:2003

SLOVENSKI STANDARD
01-januar-2005
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Advanced technical ceramics - Methods of test for ceramic coatings - Part 7:
Determination of hardness and Young's modulus by instrumented indentation testing
Hochleistungskeramik - Verfahren zur Prüfung keramischer Schichten - Teil 7:
Bestimmung der Härte und des Elastizitätsmoduls durch instrumentierte Eindringprüfung
Céramiques techniques avancées - Méthodes d'essai pour revetements céramiques -
Partie 7: Détermination de la dureté et du module de Young par essai de pénétration
instrumenté
Ta slovenski standard je istoveten z: CEN/TS 1071-7:2003
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 1071-7
SPÉCIFICATION TECHNIQUE
TECHNISCHE SPEZIFIKATION
July 2003
ICS 81.060.30
English version
Advanced technical ceramics - Methods of test for ceramic coatings -
Part 7: Determination of hardness and Young's modulus by
instrumented indentation testing
Hochleistungskeramik – Verfahren zur Prüfung Céramiques techniques avancées – Méthodes d’essai pour
keramischer Schichten – Teil 7: Bestimmung der Härte und revêtements céramiques – Partie 7: Détermination de la
des Elastizitätsmoduls durch instrumentierte dureté et du module de Young par essai de pénétration
Eindringprüfung instrumenté
This Technical Specification (CEN/TS) was approved by CEN on 19 January 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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COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2002 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TS 1071-7:2003 E
worldwide for CEN national Members.

Contents Page
Foreword. 3
Introduction . 4
1 Scope . 4
2 Normative references . 4
3 Terms and definitions. 5
4 Apparatus and materials. 6
5 Preparation of test specimen. 7
5.1 General. 7
5.2 Surface roughness . 7
5.3 Polishing. 7
5.4 Surface cleanliness . 8
6 Test procedure . 8
6.1 Calibration of instrument and indenters . 8
6.2 Test piece. 8
6.3 Test conditions . 8
6.4 Measurement. 9
7 Data analysis and evaluation of results . 9
7.1 Composite properties. 9
7.2 Evaluation of coating hardness and modulus from in-plan indentation data:. 10
8 Test report . 11
Annex A (informative) Instrumented Indentation Testing (IIT) . 16
A.1 Principles of IIT . 16
A.2 Instrument calibration procedures. 17
A.2.1 General. 17
A.2.2 Force and displacement. 17
A.2.3 Instrument frame stiffness and indenter area function . 17
A.3 Determination of the zero point. 22
A.4 Analysis Method . 24
A.4.1 Introduction . 24
A.4.2 Determination of contact depth. 24
Annex B (informative) Indenter cleaning procedure. 29
Bibliography . 30
Foreword
This document (CEN/TS 1071-7:2003) has been prepared by Technical Committee CEN/TC 184 “Advanced
technical ceramics”, the secretariat of which is held by BSI.
This document has been prepared under a mandate given to CEN by the European Commission.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to announce this Technical Specification: Austria, Belgium, Czech Republic, Denmark,
Finland, France, Germany, Greece, Hungary Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway,
Portugal, Slovakia, Spain, Sweden, Switzerland and the United Kingdom.
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
Part 8: Determination of adhesion by the Rockwell indentation test
Part 9: Determination of fracture strain
Part 10: Determination of coating thickness by cross section
Part 11: Determination of internal stress by the Stoney formula
Parts 7 to 11 are Technical Specifications.
This Technical Specification includes informative annexes A and B and a bibliography.
Introduction
The hardness and Young’s modulus of a ceramic coating are critical factors determining the performance of
the coated product. Indeed many coatings are specifically developed to provide wear resistance that is
usually conferred by their high hardness. Measurement of coating hardness is often used as a quality control
check. Young’s modulus becomes important when calculation of the stress in a coating is required in the
design of coated components. For example, the extent to which coated components can withstand external
applied loads is an important property in the application of any coated system.
It is relatively straightforward to determine the hardness and Young’s modulus of bulk materials using
instrumented indentation, However, when measurements are made normal to a coated surface, depending on
the load applied and the thickness of the coating, the substrate properties can influence the result. The
purpose of this Technical Specification is to provide guidelines for conditions where there is no significant
influence of the substrate, and, where such influence is detected, to provide possible analytical methods to
enable the coating properties to be extracted from the composite measurement. In some cases the coating
property can be determined directly from measurements on a cross-section.
Currently no standards exists to define usage of instrumented indentation testing of bulk materials, so that the
operating principles and calibration of the instruments used is described in annex A. ISO 14577 Parts 1-3 are
being drafted which cover instrumented indentation testing for the entire range from macro through micro- to
nano-indentation experiments for bulk materials. The procedures detailed in Annex A complement those in
the ISO standards, but place more emphasis on the nano/micro range applicable to thin coatings.
1 Scope
1.1 This part of EN 1071 describes a method of measuring hardness and Young’s modulus of ceramic
coatings by means of Instrumented Indentation Testing (IIT) using instruments capable of measuring force
and displacement as a function of time during the indentation process. This class of instruments includes
instruments previously known as “Depth Sensing Indenters, DSI” and “Mechanical Microprobes.”
1.2 The method is limited to the examination of single layers when the indentation is carried out normal to
the test piece surface, but graded and multilayer coatings can also be measured in cross-section if the
thickness of the individual layers or gradations is greater than the spatial resolution of the indentation process.
The latter is dependent upon instrument design and is determined by the displacement sensitivity and the
precision of location of the indents.
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 ISO 17025: General requirements for the competence of testing and calibration laboratories (ISO/IEC
17025:1999).
ASTM D-1474 Indentation Hardness of Organic Coatings.
ASTM B578-87 Microhardness Testing of Electroplated Coatings (reapproved 1993). NR
ISO/DIS 14577-1 Instrumented Indentation Test for Hardness and Materials Parameters - Part 1: Test
Method.
ISO/DIS 14577-2 Instrumented Indentation Test for Hardness and Materials Parameters - Part 2: Verification
and Calibration of Test Machines.
ISO/DIS 14577-3 Instrumented Indentation Test for Hardness and Materials Parameters - Part 3: Calibration
of Reference Blocks.
3 Terms and definitions
For the purposes of this Technical Specification, the following terms and definitions apply.
3.1
hardness, H
resistance to permanent deformation
EXAMPLE resistance to fracture damage is generally conferred by higher toughness and ductility, or lower H.
NOTE 1 With IIT, equation (1) in A.1.1 defines hardness as the maximum force, in Newtons, divided by the projected
contact area (cross-section), in square metres, that the indenter makes with the test piece at maximum force and thus has
the units of Pa. This definition is in accord with that generally agreed and first proposed by Meyer [27], and it should be
observed that the projected contact area is assumed to remain constant during elastic unloading. (see Figures A.1 and
A.2). This is an approximation and refinements to this approach are being developed [1].
NOTE 2 The term Martens Hardness, HM, (previously Universal Hardness) has been recently agreed to describe the
total deformation during indentation and is the maximum force divided by the surface area of the indenter penetrating
beyond the initial surface of the test piece at maximum force. Thus, this definition includes both plastic and elastic
deformation of the test piece. (see Figures A.1 and A.2).
NOTE 3 It is important to use the correct area function. Indentation modulus, E and indentation hardness, H , both
IT IT
require calculation of the cross-sectional (Projected) area, Ap(hc), of the indenter that is in contact with the test-piece whilst
under maximum load. HM uses a calculation of surface area, A (h ), of the indenter but does not attempt to model the
s max
bowing of the surface and makes the simplifying assumption that all of the indenter penetrating below the original surface
is involved. Vickers hardness, HV, measures the projected area of the residual indent and then calculates the surface area
of a perfect Vickers pyramid with the same projected area. This is roughly equivalent in cases of nearly perfectly plastic
materials (e.g. metals) to a function A (h ) and so there can be a scaling factor equivalence between HV and H for certain
s c IT
materials. In practice, the blunt tip of real indenters means that, as indentation depths are reduced, there is a divergence -
HV becomes infinite and H measures the mean pressure of indentation but ceases to be a measure of plasticity as the
IT
pressure drops below the plastic yield stress.
3.2
stiffness, S
contact stiffness - resistance to elastic deformation, slope of the unloading curve at maximum force (see
Figure A.1)
3.3
contact depth, h
c
depth of the indenter in contact with the test piece at maximum force
NOTE This is commonly approximated by the tangent depth adjusted for indenter geometry hc = hmax - (hmax - hr)
where is 1 for a flat indenter, 0.73 for a conical and 0.75 for paraboloid (see Figure A.1)
3.4
projected contact area, A
c
projected area (cross-sectional area) of the indenter at the contact depth
3.5
indenter area function
mathematical relationship or “look-up” table giving the projected area of an indenter as a function of distance
from the tip
3.6
depth intercept of tangent to unloading curve, h
r
extrapolation of the tangent to the elastic unloading curve at maximum force to zero load (see Figure A.1)
3.7
residual penetration depth, h
p
depth of the residual indentation (see Figures A.1 and A.2)
3.8
frame stiffness, S
f
stiffness of the instrument frame (see clause A.3.3.2)
4 Apparatus and materials
Instrumented indentation allows the direct measurement of hardness and Young’s modulus from indentation
experiments where the indentation process is continuously monitored with respect to force and displacement.
The experiments can be performed under force or displacement control. A schematic diagram of typical
equipment is shown in Figure 1. The principles of these instruments are described in detail in annex A, clause
A.1.
A variety of instrumented indentation instrument types is commercially available which have a maximum force
ranging between about 100 mN and 1000 mN; most of these can operate in either displacement or load
control modes. Also many laboratory built instruments are in operation. For instruments complying with this
Technical Specification it shall be possible to traceably measure force and displacement continuously during
the loading and unloading cycle. It is also necessary to be able to determine the point of contact with the test
piece surface.
Calibration procedures for instrumented indentation instruments are described in annex A, clause A.2.
While it is not a requirement, it is useful for an optical microscope to be incorporated in the instrument to allow
selective positioning of the indents.
NOTE Instrumented indentation apparatus equipped with AFM to assess the indent shape allows the determination
of possible pile-up or sink-in of the surface around the indent. These surface effects result in an increase (pile-up) or
decrease (sink-in) of the contact area and hence may influence the measured results. Pile-up generally occurs for fully
work hardened materials. Pile-up of soft, ductile materials is more important for thinner coatings due to the constraint of
the stresses in the coating zone of plastic deformation. It has been reported that the piled up material results in an
effective increase of the contact area for the determination of hardness, while the effect is less pronounced (about 50 %)
for the determination of Young’s modulus, since the piled up material behaves less rigidly [1,2].
5 Preparation of test specimen
5.1 General
For reasons given below, provided the surface roughness criteria in 5.2 can be satisfied the best surface
preparation is to do nothing other than to remove contaminants such as dust, fingerprints and preservative oils
etc., as described in 5.3.
5.2 Surface roughness
The final surface finish shall be as smooth as available experience and facilities permit. Recommended R
a
value shall be 5 % of the maximum penetration depth achieved whenever possible.
NOTE 1 Indentation into rough surfaces will lead to increased scatter in the results with decreasing indentation depth.
Clearly when the roughness value, R , approaches the same value as the indentation depth the contact area will vary
a
greatly from indent to indent depending on its position relative to peaks and valleys at the surface.
NOTE 2 It has been shown that for a Berkovich indenter when the angle that the surface presents to the axis of
o
indentation is greater than 7 significant errors result [3].
NOTE 3 While R has been recommended as a practical and easily understood roughness parameter, it should be
a
borne in mind that this is an average and thus single peaks and valleys may be greater than this as defined by the Rz
value, although the likelihood of encountering the maximum peak, for example, on the surface is small. Modelling to
investigate the roughness of the coating surface has concluded that there are two limiting situations for any Ra value.
When the ‘wavelength’ of the roughness (in the plane of the coating surface) is much greater than the indenter tip radius,
the force-penetration response is determined by the local coating surface curvature, but when the wavelength is much less
than the tip radius, asperity contact occurs and the effect is similar to having an additional lower modulus coating on the
surface.
NOTE 4 In cases where coatings are used in the as-received condition, nevertheless, random defects occur such as
nodular growths or scratches and where an optical system is included in the IIT instrument, it is recommended that “flat”
areas away from these defects are selected for measurement.
5.3 Polishing
Grinding and polishing shall be carried out such that any stress induced by the previous stage is removed by
the subsequent stage and the final stage shall be with a grade of polishing medium appropriate to the
displacement scale being used in the test.
NOTE 1 It should be appreciated that mechanical polishing of surfaces may result in a change of the residual stress
state of the surface and consequently the measured hardness. For ceramics this is less of a concern than for metals
although surface damage may occur.
NOTE 2 Many ceramic coatings replicate the surface finish of the substrate. If it is acceptable to do so, surface
preparation problems can be reduced by ensuring that the substrate has an appropriate surface finish, thus eliminating the
need to prepare the surface of the coating. In some cases, however, changing the substrate surface roughness may
affect other coating properties therefore care should be taken when using this approach.
NOTE 3 During the deposition of coatings it is common for there to be relatively large residual stresses arising from
thermal expansion coefficient mismatch between the coating and the substrate and / or stress induced by the coating
growth process. Thus, a stress free surface would not normally be expected. Furthermore, stress gradients in coatings
are not uncommon, so that removal of excessive material during a remedial surface preparation stage may result in a
significant departure from the original surface state.
NOTE 4 Polishing reduces the coating thickness and so the effects of the substrate will be enhanced when indenting
in-plan. The data analysis requires an accurate knowledge of the coating thickness indented and so polishing may require
re-measurement of coating thickness. This again emphasises the need to carry out minimum preparation.
5.4 Surface cleanliness
Generally, provided the surface is free from obvious surface films, no special cleaning procedures are
required. If cleaning is required the surface shall be wiped with a lintless tissue soaked in solvent to remove
trapped dust particles and the surface shall be rinsed in a solvent which will remove contaminants picked up
during exposure to the working environment, but which is chemically inert to the coating.
6 Test procedure
6.1 Calibration of instrument and indenters
6.1.1 The instrument shall be calibrated according to the procedures set out in annex A and all systems
required for the test shall be operating correctly.
6.1.2 If not established in previous tests, the area function for the indenter to be used shall be measured -
see clause A.2.3.3.
6.1.3 In all cases a reference material shall be introduced and initial indentation experiments shall be made
with this material to ensure calibrations are valid and that no damage or contamination has occurred to the
indenter tip. If the results of these initial indentations indicate the presence of contamination or damage then
the indenter should be cleaned using the procedure recommended in annex B before further trial indents are
made. If after cleaning, indentation into the reference material still indicates the presence of contamination or
damage then inspection with an optical microscope at a magnification of 400x is recommended. Detection of
submicroscopic damage or contamination is possible using scanned probe microscopy of indents or the
indenter. Where damage is detected the indenter shall be replaced and appropriate calibration procedures
implemented before the instrument is used.
6.2 Test piece
The test piece shall be mounted using the same methods as employed for determination of the instrument
frame stiffness, and shall be such that the test surface is normal to the axis of the indenter.
NOTE 1 The surface of the test piece should be flat. A useful guideline is that the R value should be less than 5 % of
a
the maximum displacement.
NOTE 2 Generally surface preparation of the test piece should be kept to a minimum, and if possible, the test piece
should be used in the as-received state if surface flatness is consistent with the criteria given in 5.2 above.
6.3 Test conditions
6.3.1 Indenter geometry, maximum force and/or displacement and load displacement cycle (with suitable
hold periods) shall be selected by the operator to be appropriate to the coating to be measured and the
operating parameters of the instrument used.
6.3.2 Indentation cycles shall be selected and where multiple indentations are planned, each indent shall be
separated from the next by at least 5 diameters of the neighbouring indent. In the case of indentation into a
cross-section of the coating, the indent shall be placed such that it is more than three times the largest indent
dimension from the coating-substrate and the coating-mountant interfaces.
NOTE It must be borne in mind that coatings can display a high degree of anisotropy, and thus the orientation of the
indenter within the plane and the direction of indentation (plan or cross-section) can significantly alter the measured value
of hardness and or modulus.
6.3.3 The specific test parameters include:
a) rate of force increase
b) rate of force decrease
c) maximum force
d) maximum displacement
e) hold times referenced to the force displacement cycle
f) indenter geometry and indenter area function
g) instrument frame compliance (stiffness)
h) distance between indents
6.3.4 The coating/substrate specific parameters include:
a) substrate hardness, Young’s modulus and Poisson’s ratio
b) coating thickness
c) surface roughness
d) adhesion of the coating to the substrate
e) coefficient of friction between coating and indenter
NOTE 1 Hardness and Young’s modulus values may be affected by adhesion [4-8].
NOTE 2 Modelling suggests that friction between the coating and the indenter has a negligible effect [1].
6.3.5 All the parameters given in 6.3.3 and 6.3.4 shall be kept constant if a direct comparison is to be made
between two or more test pieces.
NOTE Variations in test piece parameters other than hardness or modulus can affect measurement of these
quantities. It is possible that if the indentation depth is a sufficiently small fraction of the coating thickness, (e.g. < 10 % for
hardness or < 3 % - 5 % for modulus measurement) it may not be necessary to keep it constant for a direct comparison.
The exact limits depend on the ratio of properties of coating and substrate. It is recommended that methods for
normalising results to determine coating properties from coatings of different thickness be used if coating thickness is
unknown or varies.
6.4 Measurement
6.4.1 Introduce the prepared sample and position it so that testing can be undertaken at the desired
location.
6.4.2 Carry out the predetermined number of indentation cycles using the appropriate conditions.
6.4.3 Calculate the hardness and modulus of the test coating using the procedure described in 7 below.
7 Data analysis and evaluation of results
7.1 Composite properties
The hardness and indentation modulus of the test piece can be calculated using equations (1), (2) and (3)
of annex A, clause A.1. However, before this can be done using the data obtained during the indentation
experiments it is necessary to determine the values of A (projected contact area between the indenter
c
and the test piece at maximum force) and S (the sample stiffness). Clause A.4 describes the
determination of these parameters.
The properties thus calculated are composite properties for the coating/substrate combination. For
indentation into a cross-section these properties can be considered to be those of the coating, provided
that the recommendations in 6.3.2 have been followed. In the case of in-plan indentations, 7.2 provides
guidelines for extracting the hardness and indentation modulus of the coating from the composite
properties calculated.
7.2 Evaluation of coating hardness and modulus from in-plan indentation data:
7.2.1 Test parameters for ductile and brittle coatings need to be considered separately. However, in both
cases, measurement of coating thickness, t , is highly recommended for reproducible measurement of coating
c
properties. In both cases a set of trial indentations shall be performed (e.g. at two widely spaced forces) and
analysed to enable estimates of force vs. indentation depth, h , and the radius of the contact area, a, to be
c
determined. For indenters of different geometries (e.g. Berkovich, Vickers, spherical, cone, etc.), a is
approximated by the radius of a circle having the same area as that in contact with the indenter,
A
c
a
This value clearly has exact equivalence for a spherical or conical indenter but becomes increasingly less
physically meaningful as the axial symmetry of the indenter reduces, i.e. Cone = Sphere > Berkovich >
Vickers > Knoop. For in-plan indentation, elastic deformation of the substrate will always occur for all
coatings, even though this could be negligibly small for a thick compliant coating on a stiff substrate. Thus the
measured modulus will be the composite modulus of the coating and substrate and the value obtained will be
a function of indentation depth. For hardness measurement it is recommended to use as small (i.e. as sharp)
a radius indenter as possible and determine experimentally the onset of substrate plastic deformation and the
substrate hardness. Then carry out indentation experiments such that the critical displacement is not
exceeded.
NOTE 1 Empirical guidelines are given in BS 5411 Pt 6 for hardness measurement of electroplated coatings on steels,
where it is recommended that the indentation depth does not exceed one tenth the thickness of the coating, while for paint
films (ASTM D-1474) penetration of up to one third the coating thickness may be allowed. These approximations can be
unsatisfactory in many cases.
NOTE 2 It is relatively easy to measure the hardness of ductile coatings or the elastic modulus of brittle coatings. It is
more difficult to determine the hardness of brittle or hard coatings or the elastic modulus of ductile coatings.
NOTE 3 There is a compromise between: a) using a sufficiently high load (e.g.close to but not exceeding the limit
corresponding to the onset of plastic deformation of the substrate) in order to obtain the maximum of force-depth data
thereby improving the precision of the measurement; and b) indenting at a low enough displacement such that the plastic
zone of the indentation does not interact with the substrate/coating interface – thus minimising the influence of the
substrate on the measurement.
NOTE 4 Care should be taken when using the above approaches for multilayer or graded coatings.
NOTE 5 Where t is not measured nominal values of t may be used.
c c
7.2.2 For modulus measurement of ductile coatings a maximum hold period shall be used that is sufficiently
long to eliminate creep effects.
NOTE 1 Apparent rate sensitivity is often dominated by creep. A combination of a long hold at maximum load and a
high removal rate of the test force is the best strategy for minimising the effect of creep on the measurement of contact
compliance and subsequent calculation of modulus. The coating modulus may be obtained by taking a series of
measurements at different indentation depths and extrapolating a linear fit to indentation elastic modulus vs. a / t to zero.
c
This method provides a first approximation in the regime a / tc < 1.5. Indentation load or displacement and indenter
geometry shall be chosen such that data shall be obtained in the region where a/t < 1.5 (see Figure 2).
c
NOTE 2 The same parameter, a/t , can be used for the hardness results. However, since hardness is only defined for
c
pointed indenters, the non-dimensional parameter hc /tc (ratio of contact depth to coating thickness) can also be used and
gives a more sensitive measure of normalised coating thickness (since h << a). For indentation hardness measurement
c
of ductile coatings, a linear extrapolation to zero of a hc/tc plot gives a first approximation to the coating hardness, provided
the substrate hardness is not exceeded. The potential limit of the h /t is a function of the hardness ratio of the coating
c c
and substrate. For example, Au coating on Ni the hardness ratio is ~ 2.5 and hc/tc is < 1 and for an Al coating on optical
glass (BK7) with harness ratio of ~ 8 h /t is ~ 5.
c c
7.2.3 The indentation load or displacement and the indenter geometry shall be chosen such that data is
obtained in the region a/t < 2 (see Figure 3).
c
NOTE 1 For coating modulus measurement of hard coatings extrapolation of a linear fit to indentation elastic modulus
vs. a/t to zero gives a first approximation in the range a/t < 2. However, in general, a non-linear relationship appears to
c c
apply and can be reproduced by FEA analysis. The exact nature of this non-linear relation is not known and so a linear fit
over the restricted range indicated is a reasonable first approximation but is not applicable over a range wider than this.
NOTE 2 The hardness of hard or brittle coatings can only be determined with a sharp (small tip radius) indenter that
causes yielding within the coating. In general, this will only occur when hc / tc < 0.5. It is recommended that an elastic
stress analysis of the coating/substrate system be undertaken using the approximation of a spherical indenter of a radius
equivalent to the tip radius of the pointed indenter. This will determine whether the coating or the substrate will yield first
during indentation and if it is possible to determine the coating hardness at all. It is recommended that hardness values for
the substrate be obtained for comparison, by testing if necessary. Delamination or fracture of the coating can be
recognised by the hardness values obtained clustering at the substrate value, even at low hc / tc. It should be noted,
sharper indenters may cause fracture at lower loads than more blunt indenters.
7.2.4 The indentation load or displacement and indenter geometry shall be chosen such that a plateau in
the H (indentation hardness) vs h /t (or ~ a/t ) is observed (see Figure 4). The H value of his plateau is a
IT c c c IT
minimum estimate of the coating hardness. If indentation of a thicker coating yields the same value, then this
is a strong indicator that this is the value for the coating.
NOTE 1 The extent of substrate plastic deformation will depend upon a number of factors including the relative
difference in hardness and modulus between the coating and the substrate, adhesion, the coating thickness, the indenter
radius of curvature (‘sharpness’) and the maximum force. Premature yielding of the substrate may be a particular problem
in the case of hard and stiff coatings on softer substrates. However, if the film modulus is much less than the substrate
modulus, premature yielding of the substrate may also be caused e.g. SiO on W.
NOTE 2 Different procedures have been published which suggest methods that may be used to determine the onset of
substrate plastic deformation by the evaluation of the loading branch of the indentation hysteresis curve, but none has yet
been validated by the international community. These involve a method proposed by Rother and co-workers [9] in which
the differential of the load with respect to displacement is plotted versus displacement, and the point of inflection is taken
to be the depth at which plastic deformation of the substrate occurs. Hainsworth and co-workers [10] propose that
departure from a linear relationship of force versus the square of displacement is also an indication of the onset of plastic
deformation of the substrate. However, there is no guarantee that the yield or deviation detected is that of the substrate.
Also, there is always a slight deviation from the linear relationship especially for depths below 0.5 μm where the tip
rounding has an influence.
NOTE 3 Both analytical and numerical models have been proposed for indentation of coating systems. Analytical
models are usually only applicable to elastic deformation. As with the experimental approach, none of these have yet
been validated by the international community. References [11-22] list some of the approaches being developed. For
multilayer coatings or coatings with a gradation in properties modelling is clearly much more difficult, and no generally
accepted models are available. If wholly elastic measurements are possible, for instance using spherical indenters with a
large enough radius, an exact calculation of the coating modulus from the measured composite value is possible [23-26].
8 Test report
The test report shall be in accordance with EN ISO 17025 and shall contain the following information:
f) name and address of the testing establishment;
g) date of the test, unique identification of the report and of each page, customer name and address;
h) reference to this Technical Specification, i.e. CEN/TS 1071-7;
i) manufacturer and type of instrument;
j) description of the test material (material type, manufacturing code, batch number, date of receipt, and any
other relevant information);
k) test piece condition (dimensions, coating thickness, coating type and number of layers, if known, test
piece preparation procedure and surface roughness in R values and substrate composition, hardness
a
and Young's modulus);
l) procedures adopted for calibration of force, displacement, instrument frame stiffness and indenter area
function, including the choice of reference material used for calibration and checking instrument
repeatability;
m) loading/unloading cycle selected, including hold periods and stating whether a correction for thermal drift
was applied and, if so, the method used;
n) distance between indents;
o) method used to determine surface contact (zero point);
p) method chosen for the analysis of data to determine the contact depth and any models used to calculate
coating properties;
q) the test data (hardness and modulus), together with an uncertainty statement at the 95 % confidence limit
which includes measurement and calibration errors (see ISO GUM). Hardness and modulus values shall
be expressed as H and E respectively and reported in GPa;
c c
r) any other relevant comments, noting, for example, where different procedures to those recommended
have been used.
Key
1) Current source
2) Digitize
3) Displacement defecting electronics
4) Table control 100 nm/step
5) Micro computer
6) X-Y table
7) Force
8) Coil
Figure 1 — Schematic representation of a typical load displacement instrument - some instruments
operate in the horizontal plane
0 0.5 1 1.5 2 2.5 3
a/t
c
Figure 2 — Indentation reduced elastic modulus vs. normalised coating thickness Au on Ni, selected
data for spherical, Berkovich and Vickers geometries [1]
E*  /GPa
IT
0 1 2 34 5 6 7 8
a/t
c
Figure 3 — Indentation elastic modulus vs. normalised coating thickness DLC on Steel selected data
plotted with values calculated from FEA simulation. Solid line is a non-linear fit to the FEA data [1]
tc = 2510nm
tc = 1470nm
tc = 460nm
0.2 0.6 1 1.4
0 0.4 0.8 1.2
h /t
c c
Figure 4 — Indentation hardness vs. normalised coating thickness DLC on Steel, selected data
showing the effect of substrate yield for the thinnest coating. Data from Berkovich and Vickers
indenter geometries [1].
E*  /GPa
IT
E*  /GPa
IT
Annex A
(informative)
Instrumented Indentation Testing (IIT)
A.1 Principles of IIT
A.1.1 This experimental method has two major advantages over conventional macro-hardness and micro-
hardness test methods. Firstly, subjective estimation of the indent size normally needed for hardness
measurement is eliminated from the test, and, secondly, from the same indentation experiment, analysis of
the unloading curve (and input of an estimate for Poisson ratio) allows calculation of indentation modulus
which, for isotropic homogenous materials, approaches Young’s modulus.
Hardness, H, is defined as:
P
max
H                                         (1)
A
c
where F is the maximum force and A is the projected contact area between the indenter and the test piece
max c
at maximum force.
A.1.2 A is determined from the load displacement curve and knowledge of the area function of the indenter
c
- see clause A.2.3.3.
A.1.3 The area function of the indenter cannot be assumed to be that of the theoretical shape, since all
pointed indenters will have some degree of rounding at the tip and spherically-ended indenters (spherical and
conical) are unlikely to have a uniform radius. The determination of the exact area function for a given
indenter is particularly important at small (< 6000 nm) indentation depths if the induced errors are to be kept
below 1 %.
A.1.4 The reduced indentation modulus, E , is defined as:
r
S
E                                 (2)
r
A
c
where
2 2
1 1 - 1 - IT i
=  +    (3)
Er E IT Ei
and S is the contact stiffness between the indenter and test piece, that is the derivative of the initial unloading
curve after correction for frame stiffness at maximum force (dP/dh), and E and  refer to the Young’s modulus
and Poisson’s ratio of the materials, respectively, where subscripts IT and i indicate properties of the test
piece and indenter.
NOTE 1 Compliance is the reciprocal of stiffness.
NOTE 2 For diamond, the usual material used for indenters; accepted values of Ei and i are 1140 GPa and 0.07,
respectively, [28].
A.1.5 Figure A.1 is a typical load / displacement curve showing the parameters to be derived for the
determination of H and E. All values needed for calculation of hardness and Young’s modulus can be derived
directly from the load / displacement curve except the contact area. A full description is given in clause A.4.
A.1.6 Indentation experiments may be performed with a variety of differently shaped indenters which are
chosen to optimise the plastic an
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