ISO 4821:2022

INTERNATIONAL ISO
STANDARD 4821
First edition
2022-05
Plain bearings — Dynamic adhesion
test method for DLC coated parts
under lubricated condition
Paliers lisses - Méthode d'essai d'adhérence dynamique sur des
composants revêtus de DLC dans des conditions de lubrification
Reference number
ISO 4821:2022(E)
© ISO 2022

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ISO 4821:2022(E)
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© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
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ISO 4821:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Specimens. 2
4.1 General . 2
4.2 Ball specimen . 2
4.3 Disk specimen . 2
5 Apparatus . 2
5.1 Testing equipment . 2
5.2 Specification of ball-on-disk equipment . 2
5.3 Sample of disk holder . 3
5.4 Sample of ball holder . 3
5.5 Oil bath and equipment for controlling oil temperature . 4
5.6 AE sensor and its holder. 5
5.7 AE sensor amplifier . 6
5.8 Universal counter for AE events . 6
6 Testing procedure . 6
6.1 Pre-treatment of specimen before test . 6
6.2 Set up of adhesion test . 6
6.3 Lubricant . 6
6.4 Testing conditions for adhesion test . 6
6.5 Measurement of AE events . 7
6.6 Number of test repeats . 8
7 Recommendation. 8
7.1 Measurement of friction force . 8
7.2 Observation of disk after the test . 8
7.3 Observation of balls after the test . 8
8 Test report . 9
Annex A (informative) Example of stages for adhesion strength tests of coatings applied
to engine parts .10
Annex B (informative) Example of the dynamic adhesion test result relationship between
the cam/follower tester and ball-on-disk tester .11
Bibliography .13
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ISO 4821:2022(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
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 documents 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).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
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on the ISO list of patent declarations received (see www.iso.org/patents).
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www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 123, Plain bearings, Subcommittee SC 7,
Special types of plain bearings.
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.
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ISO 4821:2022(E)
Introduction
Reducing the mechanical loss in engines is one of the effective ways to improve the fuel efficiency of
automobiles. To reduce the friction coefficient between engine parts, diamond-like carbon (DLC)
coatings can be applied for plain bearings as well as other sliding parts such as valve lifters and piston
rings.
Since DLC hard coatings have high internal stress due to its coating process under high temperature
and the difference of the coefficient of thermal expansion between DLC and engine parts, the quality
control of the adhesion strength between coatings and base materials of specific parts after the coating
process is very important. As there is no appropriate official test, automobile manufacturers or part
suppliers must validate the adhesion strength by using a specially designed test facility using actual
engine parts. In order to further spread the DLC coatings to mechanical parts of engines in the future, a
test method can be used to easily evaluate the adhesion strength of the coatings.
The purpose of this document is to provide a test method for evaluating adhesion strength of DLC
coatings. The test method specified in this document is a test apparatus equipped with a simple ball-
on-disk that has a correlation with conventional engine evaluation results and a relatively inexpensive
acoustic emission measurement machine without using actual parts.
The positioning of this test method in the process of parts evaluation performed by automobile
manufacturers or part suppliers is shown in Annex A. The correlation between results obtained by the
test method specified in this document and results obtained by the test method using conventional
engine parts is described in Annex B.
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INTERNATIONAL STANDARD ISO 4821:2022(E)
Plain bearings — Dynamic adhesion test method for DLC
coated parts under lubricated condition
1 Scope
This document specifies a procedure to measure the adhesion strength of diamond-like carbon (DLC)
coatings specified in ISO 20523 by detecting acoustic emission signals using ball-on-disk method under
the lubricated condition. DLC is normally coated on metal or ceramic.
The test results are not applicable when the DLC coated parts operate in an unlubricated environment.
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 683-17, Heat-treated steels, alloy steels and free-cutting steels — Part 17: Ball and roller bearing steels
ISO 1101, Geometrical product specifications (GPS) — Geometrical tolerancing — Tolerances of form,
orientation, location and run-out
ISO 21920-2, Geometrical product specifications (GPS) — Surface texture: Profile— Part 2: Terms,
definitions and surface texture parameters
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
ball-on-disk method
test method in which the sliding contact between fixed balls and rotating disk specimen
3.2
acoustic emission
AE
physical vibration caused by sudden movement within a material subjected to physical stress, often
symptomatic of a defect
3.3
adhesion strength
load of diamond-like carbon (DLC) coating delamination detected by sharp signal increment of acoustic
emission (3.2)
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ISO 4821:2022(E)
4 Specimens
4.1 General
Ball and disk specimens having the dimensions described later are prepared. To load equally on each
ball, three balls shall be applied. In the ball-on-disk test, a bearing ball is fixed and used. The disk can
be used as a substrate for a DLC film for testing. All appropriate details regarding the ball and disk
specimens shall be provided, such as their dimensions, surface finish, material type, composition,
microstructure, and processing.
4.2 Ball specimen
The ball specimen shall be 9,525 mm in diameter, made of 100Cr6 material as specified in ISO 683-17,
and is recommended to be the equivalent to G28 or more as specified in ISO 3290-1. The hardness of the
ball is HRC 62-67.
4.3 Disk specimen
The thickness of the disk specimen is 2,5 mm or more. The thickness of the DLC film is 0,1 μm to 10 μm.
In order to set the sliding radius of the ball to 9 mm, the diameter of the test specimen is 28 mm or
more. If the disk has a hole inside, the acceptable inner diameter is 12 mm or less. The surface of the
disk shall be flat and parallel within 0,02 mm as specified in ISO 1101. The roughness of the test surface
shall be less than 0,02 μm Ra as defined in ISO 21920-2. The hardness of the substrate is recommended
to be HRC 60 or more, or 700 HV or more.
5 Apparatus
5.1 Testing equipment
Adhesion strength test using ball-on-disk testing equipment shall consist of the following:
a) the disk holder, for securing a disk specimen;
b) the ball holder, for fixing ball specimens;
c) the equipment, for driving the disk while pressing the ball against the disk with stepwise load;
d) the equipment, for measuring the friction force;
e) the oil bath maintaining lubrication and its temperature;
f) the oil heater, for controlling the oil temperature;
g) the acoustic emission (AE) sensor, for detecting delamination of DLC coating;
h) the AE sensor holder, for detecting AE by way of ball specimens;
i) the equip
...