ISO 14577-6:2025

Metallic materials — Instrumented indentation test for hardness and materials parameters — Part 6: Instrumented indentation test at elevated temperature

This document specifies the instrumented indentation method for testing at elevated temperature for determination of hardness and other materials parameters at temperatures above ambient. Elevated temperature testing is defined in this document to be when the test piece and indenter tip are heated above the ambient conditions of the instrument to a controlled and measured temperature; insulating shielding is used to enclose the hot zone to reduce heating effects so that the majority of the instrumented indentation testing machine is at ambient conditions. This document is restricted to test machines that have been traceably calibrated and pass an indirect verification according to ISO 14577-2 when operating at elevated temperature to ensure that any effects on ambient sensors caused by the presence of a hot zone are accounted for. This document covers instrumented indentation testing at elevated temperatures in air, in inert or reducing gaseous environments, or in vacuum. This document provides a method for instrumented indentation testing at elevated temperature with both the indenter tip and test piece actively heated, and with independent feedback control and temperature measurement of both the indenter tip and test piece. This document provides a method for estimation of the uncertainty of the contact temperature. The uncertainty increases as the thermal conductivity of the test piece decreases. It is left to the user to decide if that uncertainty is fit for their purpose. The test method in this document is not applicable to: — instrumented indentation testing where there is no direct measurement of the temperature of the indenter tip body itself; — instrumented indentation testing where above ambient temperatures are obtained by placing the entire instrument in a hot box to achieve iso-thermal heating of the whole system. These systems typically only achieve limited elevated temperature; — instrumented indentation testing with active heating of the test piece but only passive heating of the indenter, e.g. by proximity to the hot test piece and thermal conduction through the indentation contact, hot gas, or any combination.

Matériaux métalliques — Essai d'indentation instrumenté pour les paramètres de dureté et de matériaux — Partie 6: Essai d'indentation instrumenté à température élevée

General Information

• Status: Published
• Publication Date: 05-Nov-2025
• ICS: 77.040.10 - Mechanical testing of metals
• Technical Committee: ISO/TC 164/SC 3 - Hardness testing
• Drafting Committee: ISO/TC 164/SC 3 - Hardness testing
• Current Stage: 6060 - International Standard published
• Start Date: 06-Nov-2025
• Due Date: 19-Oct-2025
• Completion Date: 06-Nov-2025

Standards Content (Sample)

International
Standard
ISO 14577-6
First edition
Metallic materials — Instrumented
2025-11
indentation test for hardness and
materials parameters —
Part 6:
Instrumented indentation test at
elevated temperature
Matériaux métalliques — Essai d'indentation instrumenté pour
les paramètres de dureté et de matériaux —
Partie 6: Essai d'indentation instrumenté à température élevée
Reference number
© ISO 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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or ISO’s member body in the country of the requester.
ISO copyright office
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 2
3.1 Terms and definitions .2
3.2 Symbols .2
4 Principle . 3
4.1 General .3
4.2 Instrument calibration and verification at elevated temperature .3
4.3 Indenter material selection .3
4.4 Test environment .3
4.5 Indentation creep rate at elevated temperature .3
4.6 Assigning the contact temperature .4
5 Testing machine. 4
5.1 Testing machine capability .4
5.2 Traceable calibration of the contact temperature .5
5.3 Traceable calibration of the test machine at operating temperature .5
5.3.1 Method 1 .5
5.3.2 Method 2 .5
5.4 Indirect validation .5
5.5 Test piece heating . .6
5.6 Test environment .6
5.7 Indenter and frame compliance .6
5.7.1 Indenter geometry .6
5.7.2 Indenter area function and frame compliance .6
5.7.3 Indenter tip material selection .6
5.8 Specific requirements for testing at elevated temperature .7
6 Test pieces . 7
7 Test procedure . 7
8 Results . .10
8.1 Data process and analysis .10
8.2 Indentation hardness at elevated temperature .10
8.2.1 Determination of indentation hardness at elevated temperature, H (T) .10
IT
8.2.2 Designation of indentation hardness at elevated temperature, H (T) .10
IT
8.3 Indentation modulus at elevated temperature .10
8.3.1 Determination of indentation modulus at elevated temperature, E (T).10
IT
8.3.2 Designation of indentation modulus at elevated temperature, E (T).11
IT
9 Uncertainty of results . .11
9.1 Uncertainties for testing at elevated temperature.11
9.2 Error in assigned temperature . 12
9.3 Estimation of uncertainty . 12
10 Test report .13
Annex A (informative) Reactivity of indenter and test piece combinations .15
Annex B (informative) Indenter oxidation onset temperature for various indenter materials .16
Annex C (Normative) Temperature calibration procedure . 17
Bibliography .20

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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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 164, Mechanical testing of metals, Subcommittee
SC 3, Hardness testing.
A list of all parts in the ISO 14577 series can be found on the ISO website.
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
Hardness has typically been defined as the resistance of a material to permanent penetration by another
harder material. The results obtained when performing Rockwell, Vickers, and Brinell tests are determined
after the test force has been removed. Therefore, the effect of elastic deformation under the indenter has
been ignored.
ISO 14577 (all parts) has been prepared to enable the user to evaluate the indentation of materials by
considering both the force and displacement during plastic and elastic deformation. By monitoring the
complete cycle of increase and removal of the test force, hardness values equivalent to traditional hardness
values can be determined. More significantly, additional properties of the material, such as its indentation
modulus and elasto-plastic hardness, can also be determined. All these values can be calculated without
the requirement to measure the indent optically. Furthermore, by a variety of techniques, the instrumented
indentation test is able to generate hardness and modulus values at different indentation depths within the
indentation cycle.
This document has been prepared to enable the user to obtain hardness and other materials parameters
using instrumented indentation testing at elevated temperature. The elastic and plastic properties of
material components at elevated temperature are critical for determining the performance representative
of in-service condition above ambient temperature. Typical applications include hard coatings, nuclear
materials, welded materials, fuel cell materials, aerospace materials, etc. In-service properties of wear
surfaces, cutting tool, high friction contacts are also significant applications.
This document covers the instrumented indentation testing systems with independent heating of both
the indenter and test piece with feedback control and equipped with temperature sensing. This type of
instrumented indentation testing system is suitable for testing materials of high or low thermal conductivity
in air, in inert or reducing gaseous environment, and also in vacuum, which offers the potential for higher
testing temperature. Active heating of the indenter tip allows independent adjustment of energy flow into the
tip and test piece so that a condition of iso-thermal contact is achieved rather than just thermal equilibrium
with constant (but unknown) thermal gradients. A temperature sensor mounted in an indenter body with
a low heat capacity is sensitive to small heat flows and, therefore, can detect small temperature differences
between test piece and tip.
The method described in this document can achieve low uncertainty in the temperature assigned to the
indentation contact when testing materials with high thermal conductivity (uncertainty increases when
testing low thermal conductivity materials). This is achieved by traceable calibration of the indenter
tip temperature for a reproducible temperature offset between the contact temperature and indenter
temperature sensor reading. A reproducible temperature offset is obtained by using a procedure to
minimise (optimally to zero) the heat flow between the test piece and the indenter. This not only makes
the temperature offset from indenter temperature sensor to indenter tip a reproducible amount, but also
minimises the temperature gradient in the test piece (from the contact to the bulk of the test piece) that
occurs when there is a heat flow through the contact. The minimum detectable heat flow of a system depends
upon the heat capacity of the indenter and the resolution of the indenter temperature sensor. Any amount of
heat flow causes a higher uncertainty in assigned contact temperature that is higher the lower the thermal
conductivity of the test material is.

v
International Standard ISO 14577-6:2025(en)
Metallic materials — Instrumented indentation test for
hardness and materials parameters —
Part 6:
Instrumented indentation test at elevated temperature
1 Scope
This document specifies the instrumented indentation method for testing at elevated temperature for
determination of hardness and other materials parameters at temperatures above ambient. Elevated
temperature testing is defined in this document to be when the test piece and indenter tip are heated above
the ambient conditions of the instrument to a controlled and measured temperature; insulating shielding is
used to enclose the hot zone to reduce heating effects so that the majority of the instrumented indentation
testing machine is at ambient conditions.
This document is restricted to test machines that have been traceably calibrated and pass an indirect
verification according to ISO 14577-2 when operating at elevated temperature to ensure that any effects on
ambient sensors caused by the presence of a hot zone are accounted for. This document covers instrumented
indentation testing at elevated temperatures in air, in inert or reducing gaseous environments, or in vacuum.
This document provides a method for instrumented indentation testing at elevated temperature with both
the indenter tip and test piece actively heated, and with independent feedback control and temperature
measurement of both the indenter tip and test piece.
This document provides a method for estimation of the uncertainty of the contact temperature. The
uncertainty increases as the thermal conductivity of the test piece decreases. It is left to the user to decide if
that uncertainty is fit for their purpose.
The test method in this document is not applicable to:
— instrumented indentation testing where there is no direct measurement of the temperature of the
indenter tip body itself;
— instrumented indentation testing where above ambient temperatures are obtained by placing the entire
instrument in a hot box to achieve iso-thermal heating of the whole system. These systems typically only
achieve limited elevated temperature;
— instrumented indentation testing with active heating of the test piece but only passive heating of the
indenter, e.g. by proximity to the hot test piece and thermal conduction through the indentation contact,
hot gas, or any combination.
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 14577-1, Metallic materials — Instrumented indentation test for hardness and materials parameters —
Part 1: Test Method
ISO 14577-2, Metallic materials — Instrumented indentation test for hardness and materials parameters —
Part 2: Verification and calibration of testing machines

ISO 14577-3, Metallic materials — Instrumented indentation test for hardness and materials parameters —
Part 3: Calibration of reference blocks
ISO 14577-4, Metallic materials — Instrumented indentation test for hardness and materials parameters —
Part 4: Test method for metallic and non-metallic coatings
ISO 14577-5, Metallic materials — Instrumented indentation test for hardness and materials parameters —
Part 5: Linear elastic dynamic instrumented indentation testing (DIIT)
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 14577-1, ISO 14577-2, ISO 14577-3,
ISO 14577-4, ISO 14577-5 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/
3.2 Symbols
Table 1 — Symbols and designations
Symbols Designations Unit
Projected area of contact under load of the indenter at distance h from the tip
c 2
A (T) mm
p
at elevated temperature
a Equivalent contact radius mm
C
Heat capacity of the indenter assembly J/K
p
C (T) Total measured compliance of the contact at elevated temperature nm/mN
T
C (T) Instrument compliance at elevated temperature nm/mN
f
Compliance of the contact at elevated temperature after correction for machine
C (T) nm/mN
S
compliance
E(T) Young’s modulus at elevated temperature GPa
E (T) Reduced modulus of the contact at elevated temperature GPa
r
E (T) Modulus of the indenter at elevated temperature GPa
i
E (T) Indentation modulus at elevated temperature GPa
IT
E*(T) Plane strain indentation modulus at elevated temperature GPa
F (T) Maximum applied force at test temperature N
max
h Depth of the contact of the indenter with the test piece at F (T) mm
c max
H (T) Indentation hardness at elevated temperature GPa
IT
k Thermal conductivity of the test piece W/(m·k)

Q Minimum detectable heat flow between test piece and indenter tip W
min
T Temperature of the test °C
Temperature at the contact point (this is the temperature assigned to the test
T °C
c
results)
T Temperature at the displacement measuring device °C
d
T Temperature at the force measuring device °C
f
T Temperature sensor reading for control of test piece heater °C
sh
TTaabbllee 11 ((ccoonnttiinnueuedd))
Symbols Designations Unit
Temperature sensor reading at the position of the temperature sensor in the
T °C
ih
indenter body
T Temperature sensor reading of the test piece surface °C
ss
T Temperature of the indenter at the tip °C
tip
ΔT The resolution of the indenter temperature sensor °C
ih
t Integration period when the indenter and the test piece is in contact s
i
v (T) Poisson’s ratio of the indenter at elevated temperature ‒
i
v (T) Poisson’s ratio of the test piece at elevated temperature ‒
s
4 Principle
4.1 General
Instrumented indentation tests conforming to ISO 14577-1, ISO 14577-4, or ISO 14577-5 are performed into
a test piece heated to elevated temperature (i.e. significantly higher than ambient temperature) in a hot zone
that is thermally insulated from the rest of the testing machine. The purpose of this method is to obtain
the hardness and other material properties as defined in ISO 14577-1, ISO 14577-4, or ISO 14577-5 but at a
measured temperature above the ambient conditions.
4.2 Instrument calibration and verification at elevated temperature
Although the majority of the testing machine is at ambient temperature, there are small heat leaks from the
hot zone into the instrumentation or the instrument environment, which can shift the calibrations away
from those obtained at room temperature. Therefore, the test machine shall be traceably calibrated and
pass an indirect verification in accordance with ISO 14577-2 whilst operating at the required elevated test
temperature.
4.3 Indenter material selection
The indenter material shall be carefully selected so that the indenter tip does not change during the test in
a way that prevents the intended sample property measurements during the test. The indenter tip shall not
deviate in shape or mechanical properties from its calibrated values and shall not chemically react with, or
bond to, the test piece. In all cases, the elastic modulus and Poisson’s ratio of the indenter tip (as a function
of temperature) shall be used for analysis of the indentation response and the values used shall be recorded
in the test report.
4.4 Test environment
The test environment shall be carefully selected and controlled so that it shall not degrade nor chemically
alter (e.g. oxidise) the test piece surface in a way that prevents the intended sample property measurements
during the test, so that the results returned will be from the material intended for testing and not the
properties of the degraded material or oxide instead. As temperature increases, the reactivity of tip and test
piece to oxygen increases. Therefore, the time taken to achieve thermal equilibrium and perform the tests
should be minimised.
4.5 Indentation creep rate at elevated temperature
ISO 14577-1 places a maximum limit on the allowable indentation creep rate for a given indentation cycle.
At elevated temperature, the indentation creep rate is typically higher than at room temperature. Suitable
choice of force-displacement-time cycle shall be made to meet the requirements of ISO 14577-1 and should
be optimised to minimise uncertainty in the measurement of the indentation stiffness and thermal drift.
This is dealt with in more detail in the relevant sections of this document.

4.6 Assigning the contact temperature
A temperature shall be assigned to the measured indentation response to obtain a valid temperature
dependent property measurement. The temperature assigned shall be the iso-thermal contact temperature
measured by traceably calibrated temperature sensing of a low heat capacity indenter body. Iso-thermal
contact is achieved and verified by detecting, then minimising, absolute heat flow between tip and test piece
when making and breaking indentation contact (a detailed procedure is given in 7.1).
NOTE 1 Iso-thermal contact is a special case of thermal equilibrium. A contact is in thermal equilibrium whenever its
temperature gradient is constant. This state occurs when heat flow through the contact is constant. Iso-thermal contact
is the specific state of thermal equilibrium where the heat flow between tip and test piece is both constant and zero.
NOTE 2 The heat flow into the indenter tip due to radiation from the hot test piece is a strong function of the tip to
test piece distance. This causes a change in indenter temperature as the indenter approaches contact.
NOTE 3 Instrumented indentation testing measures the indentation response of a very small volume of a test piece,
at the contact position, where it is not possible to place a temperature sensor of equivalent size and heat capacity. The
temperature offset between a thermocouple mounted elsewhere on a test piece and the actual indentation contact
position changes with: contact position, test piece size and thickness, and test piece thermal emissivity and thermal
conductivity. In contrast, the indenter construction, heat capacity, thermal conductivity, and temperature sensor to
contact distance, remains the same for every indent it performs.
5 Testing machine
5.1 Testing machine capability
The testing machine shall have the capability of applying predetermined test forces or displacements. It shall
have the capability of measuring and reporting applied force, indentation displacement and time throughout
the testing cycle and making measurements within the required scope of ISO 14577-1, ISO 14577-4 or
ISO 14577-5.
The testing machine shall have the capability to heat the indenter tip and the test piece independently of
each other using independent temperature sensors for feedback control. The indenter tip heater shall be
capable of both constant temperature and constant power feedback control. The testing machine shall have
temperature sensors for the indenter tip and the test piece, which shall both have a resolution of 0,1 °C or
better. The resolution of the indenter tip heater power controller shall be 5 mW or better. For measurements
of low thermal conductivity materials, a better resolution for both test piece and indenter temperature
sensors is strongly recommended to reduce the maximum deviation of heat flow from zero and therefore
the uncertainty in assigned temperature.
The indenter temperature sensor shall measure the temperature of the indenter body at a fixed or
reproducible position in the heated indenter assembly, which consists of those parts in good thermal contact
with the indenter. The heated indenter assembly shall have a low total heat capacity (i.e. including the heater,
if contact heating is used, the indenter, the indenter mounting body and any indenter shaft in good thermal
contact). The combination of indenter assembly heat capacity and temperature sensor resolution determines

the minimum detectable heat flow ( Q ) between test piece and tip for a defined integration period ( t )
min i
using Formula (1):
ΔTC×
ih p

Q = (1)
min
t
i
where C is the heat capacity of the indenter assembly and ΔT is the indenter temperature sensor
p ih
resolution. The integration period should be at least 60 s.
NOTE Heat flow causes the tip temperature to deviate from the iso-thermal calibrated value and generates
a temperature gradient in the test piece that changes the temperature of the small volume of material close to the
indentation contact that is generating the indentation response.

5.2 Traceable calibration of the contact temperature
The instrument shall be able to measure and assign a calibrated temperature to the indentation contact. The
temperature measuring device and the temperature offset between it and the indentation contact shall be
traceably calibrated over the entire operating temperature range (see Annex C).
If non-contact methods of temperature measurement of the test piece are to be used, the spatial resolution,
targeting accuracy to ensure a reproducible measurement position, and temperature accuracy and precision,
should be carefully considered when selecting the appropriate temperature measuring device.
5.3 Traceable calibration of the test machine at operating temperature
All instruments shall be traceably calibrated for force, displacement and instrument compliance in
accordance with ISO 14577-2 or ISO 14577-5 over the whole range of the hot zone temperatures.
Direct calibrations of the test force and displacement may be carried out using either Method 1 or Method 2.
5.3.1 Method 1
Force and displacement direct calibrations shall be carried out in accordance with ISO 14577-2 by placing the
calibration sensors outside of the hot zone in a manner that allows the direct calibration of the instrument
force and displacement whilst the hot zone is operating.
NOTE This method currently provides the lowest uncertainty calibrations. However, it can be difficult to realize
when the hot zone is enclosed and thermally insulated from the rest of the instrument.
5.3.2 Method 2
The test machine shall be directly calibrated for force and displacement at room temperature in accordance
with ISO 14577-2 or ISO 14577-5 without the hot zone operating. The temperature of the instrument force
and displacement measuring devices shall be measured as a function of the hot zone temperature over the
whole temperature operating range whilst the hot zone is operating. If there is a change in the temperature
of the measuring devices with the temperature of the hot zone, direct calibrations of force and displacement
1)
shall be carried out in accordance with ISO 14577-2:— , 4.1.1 as a function of temperature of the force and
displacement measuring devices.
NOTE The change in temperature of force and displacement measuring devices can cause different effect than a
change of global instrument temperature.
5.4 Indirect validation
ISO 14577-2 requires indirect validation of the testing machine using a reference material after direct
calibration. This shall be performed over the hot zone temperature range using a reference material certified
for elastic modulus and Poisson’s ratio vs. temperature. If a certified reference material is not available, then
a reference material whose dependence of elastic modulus on temperature is well known shall be used and
its unique ID and elastic modulus vs. temperature relationship shall be reported.
The verification of the machine compliance shall be carried out in accordance with ISO 14577-2 at ambient
temperature. For test at elevated temperature, additional verification and calibration shall be carried out
at the testing temperature using suitable reference materials, following the same procedure described in
ISO 14577-2:— Annex D. Young’s modulus and Poisson’s ratio values of reference materials at the testing
temperature of both the reference materials and the indenter materials shall be used. The reference
test pieces shall be mounted the same way as the test pieces, in order to have a mechanically equivalent
compliance.
1) Under preparation. Stage at the time of publication: ISO/DIS 14577-2:2025.

5.5 Test piece heating
The testing machine shall have the capability of creating a local hot zone with feedback control to heat the
test piece to a constant temperature significantly above the ambient temperature and maintain a constant
test piece temperature for the duration of the measurements. The hot zone shall be enclosed and insulated
from the rest of the instrument.
5.6 Test environment
The environment of the indentation contact shall be maintained such that there is no significant physical or
chemical degradation of the test piece surface or the indenter tip at the test temperatures. Requirements for
test environment and indenter tip choice depend strongly on test temperature and material type of the test
piece. At some temperatures, the testing machine may be operated in air. At high temperatures, typically
the most important requirement is to reduce the partial pressure of oxygen in the contact zone. This may be
achieved by the use of vacuum or suitable high purity gas purging.
-4 -6
NOTE A rule of thumb is that a partial pressure of 10 Pa (10 mbar) of oxygen results in a monolayer of oxygen
hitting a surface approximately every 2 seconds. Arrival rate scales with partial pressure. Typical bottled “pure” gases
can also have significant oxygen or water partial pressures. For example, 99,999 9 % (6 N) gas has an “other gases”
-4 -4 -1
partial pressure of 10 % of the gas pressure, i.e. 10 Pa per 100 Pa, which is 10 Pa at atmospheric pressure.
5.7 Indenter and frame compliance
The indenter tip shall be of a material that does not degrade by physical or chemical reaction with the test
piece at the test temperature. Non-diamond indenters shall be used where necessary for chemical inertness;
however, they are less rigid (lower E ), see Annex A and have a lower thermal conductivity.
i
The indenter area function shall be verified after each series of high temperature measurements using a
reference material (see 7.3). This verification may be performed at room temperature.
5.7.1 Indenter geometry
The indenter geometry shall conform to ISO 14577-2 (for further information on diamond indenters, see
2)
ISO 14577-2:— , Annex D). The indenter shall be fitted with a thermal break to thermally isolate it from the
rest of the testing machine (in particular the displacement/force sensors/actuators).
5.7.2 Indenter area function and frame compliance
The testing machine shall have the capability of utilizing the appropriate indenter area function and frame
compliance correction. The indenter area function and frame compliance used for the indentation test shall
be calibrated in accordance with ISO 14577-2 at ambient temperature. For tests at elevated temperature,
the indenter area function shall be validated, and the frame compliance shall be determined at the testing
temperature by following the same procedure described in ISO 14577-2:— , Annex B, using E(T) and ν (T)
i
values corresponding to the testing temperature or the range of testing temperatures to be used.
NOTE 1 Use of an iterative method and multiple reference materials permits the simultaneous measurement
of indenter area function and machine compliance correction (see Reference [1]); this is particularly useful for
instrumented indentation test at elevated temperature as the direct measurement method for determination of
indenter area function at temperature is a challenge in practice.
NOTE 2 It is assumed that the area function is constant with temperature, and that the indenter geometry will not
change as a function of temperature.
5.7.3 Indenter tip material selection
The indenter tip material shall be harder and have a higher elastic modulus than the test piece material at
the test temperature. The elastic modulus and Poisson’s ratio for the tip shall be known for the temperature
of test and used in calculating the measurement result.
2) Under preparation. Stage at the time of publication: ISO/DIS 14577-2:2025.

The chemical reaction between indenter and test piece at elevated temperature shall be carefully considered
to avoid any potential indenter damage. Indenters shall be checked for changes in area function before and
after a series of indentations at elevated temperature by performing a limited indirect validation on a single
certified reference material. The limited indirect verification shall be carried out at a minimum of two test
depths relevant to the elevated temperature tests being performed. The limited indirect verification may
be performed at ambient temperature or elevated temperature on a certified reference material that has no
chemical reactivities with the indenter and is calibrated as a function of temperature.
Diamond indenters react with oxygen and with carbide forming test pieces and shall not be used at
temperatures above 400 °C in air, see Reference [2]. To reduce the oxidation of the indenter, the experiments
should be done in vacuum or inert/reducing gas atmosphere.
NOTE 1 An overview of indenter and test piece materials classes and their reactivities at elevated temperature is
given in Annex A.
NOTE 2 Ellingham diagrams can be used to look up the Gibbs free energy of formation for equilibrium reactions.
NOTE 3 Gas purges do not exclude O completely – there will be oxidising elements present at some level in all cases.
5.8 Specific requirements for testing at elevated temperature
The indentation contact shall be in iso-thermal equilibrium (indenter tip and test piece contact point have the
same temperature) at a calibrated temperature. When these conditions are met, there is no heat flow upon
contact between the indenter tip and test piece. This ensures that there are no thermal gradients within the
indentation volume of the test piece and that the temperature offset between indenter temperature sensor
and the contact is the same as during its calibration. The sensitivity of the instrument to heat flow is a key
parameter for comparing results. The following shall be estimated and reported:
— the heat capacity of the indenter assembly;
— the resolution of the indenter temperature sensor;

— an estimation of Q the minimum detectable heat flow through the indentation contact. (See Formula 1)
min
6 Test pieces
6.1 The test piece shall be prepared in accordance with ISO 14577-1 and ISO 14577-4.
6.2 The test piece shall remain in the solid state at the temperature of measurement.
6.3 The onset temperature for oxidation of the test piece shall be considered, see Annex B. Precautions shall
be taken to limit the surface degradation of the test piece at elevated temperature, for example, enclosure
with reducing atmosphere or vacuum to minimise the surface oxidation. This is particularly important for
testing in the nano range. It is recommended to use a test piece with low thickness and low heat capacity
to reduce the time needed to achieve thermal equilibrium. The test piece shall be firmly supported with a
known instrument compliance at each test temperature. The use of high temperature cement is permitted
where it can be demonstrated that there is no significant additional uncertainty in the C (T) of the system
f
due to a variation in the thickness and composition of the cement used and that the frame compliance for the
system has been determined using the same mounting method and verified using 14577-2.
7 Test procedure
7.1 Measurement of the contact temperature shall be obtained by using the indenter itself as the
temperature sensor. The indenter tip temperature sensor calibration is determined by indenting into a
calibrated thermocouple mounted in a high thermal conductivity calibration sample as described in Annex C.
The procedure for achieving iso-thermal contact and assigning a contact temperature to an indentation for

instruments with active heating and temperature sensing of the indenter tip is given below and presented as
a flow chart in Figure 1.
Figure 1 — Flow chart to achieve an iso-thermal contact.
7.1.1 Approach the test piece until the indenter is close but a safe distance from contact.
7.1.2 Heat the test piece and the tip to the nominal test temperature, T, required by selecting a suitable
temperature set point (under PID feedback control) determined in accordance with the calibration of the
tip and test piece temperature sensors (See Annex C for calibration procedures). A stabilization period is
recommended before conducting indentation experiments, with the tip close but at a safe distance from the
test piece so that thermal expansion or drift do not cause unwanted contact, to allow the indentation system
to reach a stable thermal state that matches the state of the machine during elevated temperature calibration.
This is particularly important to consider if there has been a large change in test piece temperature and,
therefore, a significant change in heat input to the hot zone (and, therefore, heat flow from the hot zone into
the rest of the instrument).
7.1.3 Bring the indenter tip into close proximity with the sample surface (within a few micrometres) in
order to begin tuning the temperature of tip and sample to the desired test temperature.
NOTE Radiative heat exchange between the test piece, tip and the lower temperature environment means that,
the equilibrium temperatures of the tip and test piece depend on their separation. Typically, the radiative heat input
to the tip increases as the tip approaches the test piece. This increases the indenter tip temperature. This temperature
change occurs even after waiting a long time for thermal equilibrium and is significant when moving large distances
to contact (e.g. 100 µm).
7.1.4 Switch the indenter tip heater control to constant power feedback. Adjust the test piece heater
temperature or the tip heater power level to target the same temperature of tip and test piece surface when

in contact (allowing for the increase in tip temperature when moving to contact). Move the indenter to
approach the test piece slowly to allow the tip temperature to respond to the radiative heat flow changes
before coming into contact with the test piece. Contact the test piece and indent to a representative
indentation area with the contact radius preferably equal or larger than 1 micrometre and hold for at least
60 seconds, monitoring the temperature reading on the indenter temperature sensor, T . When the
ih
representative contact radius is smaller than 1 micrometre, longer integration time should be used to obtain

an acceptable Q , see Formula (1).
min
7.1.5 If the indenter temperature, T , changes as a result of contact, this indicates a flow of heat energy
ih
and a lack of iso-t
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