ISO 21874:2019

PVD multi-layer hard coatings - Composition, structure and properties

This document specifies the evaluation standard of the composition, structure and properties of multi-layer hard coatings by common physical vapor deposition (PVD), indicating a vacuum deposition method that produces a material source by evaporation, sputtering or related non-chemical ways.

Revêtements durs multicouches déposés par PVD — Composition, structure et propriétés

General Information

• Status: Published
• Publication Date: 29-Oct-2019
• ICS: 25.220.40 - Metallic coatings
• Technical Committee: ISO/TC 107/SC 9 - Physical vapor deposition coatings
• Drafting Committee: ISO/TC 107/SC 9 - Physical vapor deposition coatings
• Current Stage: 9093 - International Standard confirmed
• Start Date: 01-Jul-2025
• Completion Date: 13-Dec-2025

Overview

ISO 21874:2019 - PVD multi-layer hard coatings - Composition, structure and properties - defines standardized methods to evaluate the composition, microstructure, surface quality, thickness and mechanical/tribological properties of multi-layer hard coatings produced by physical vapor deposition (PVD). It is intended primarily for coating development and laboratory evaluation of PVD multi-layer systems (e.g., transition metal nitrides and carbides), rather than routine production QA.

Key topics and requirements

• Scope & sample preparation
  • Applies to PVD (evaporation, sputtering, arc, etc.) deposited multi-layer hard coatings.
  • Samples should be polished to mirror finish (roughness Rpk < 0.05 μm) and ultrasonically cleaned before coating and testing.
• Chemical composition analysis
  • Recommended techniques: EDS, EPMA, XPS, AES, SIMS, XRF, GDOES. Choice depends on element (B, C, N, O, metals), depth (surface vs cross-section) and destructiveness.
• Layer structure and microstructure
  • Use SEM, TEM, SIMS to characterise columnar, equiaxed or amorphous structures, multi-layer stacks, nano-layered (modulation period Λ) and superlattice coatings. Annex A provides TEM specimen guidance.
• Surface quality / deficiency rate
  • Quantify droplets, pinholes and shallow craters by SEM image analysis. Deficiency rate = (defect area / observed area). Polished coatings with ≤10% deficiency are acceptable; production-level tests recommend lower limits (example: <3% for nano-indentation-ready surfaces).
• Thickness measurement
  • Use ball crater-grinding (ISO 26423) for thickness; SEM/TEM cross-section preferred for precise layer-by-layer measurements. ISO 9220 referenced for SEM specimen prep on metallic substrates.
• Mechanical and tribological properties
  • Hardness: nano-indentation (ISO 14577-1) to avoid substrate influence (typical indentation depths ~50–200 nm); microhardness (Vickers ISO 6507-1, Knoop ISO 4545-1) requires indentation depth < 1/10 of coating thickness (Knoop better for >2 μm; Vickers for >4 μm).
  • Friction & wear: ball-on-disc style tribology testing referenced (ISO 20808).

Applications and users

• Coating developers and R&D labs validating new PVD multi-layer recipes
• Materials scientists and TEM/SEM analysts characterizing microstructure
• Tribology and wear test laboratories assessing friction/wear performance
• Tool and component manufacturers (cutting tools, forming dies, wear parts) seeking performance benchmarking
• Quality engineers adopting standard evaluation methods during process transfer and qualification

Related standards

• ISO 14577-1 (instrumented indentation)
• ISO 4545-1 (Knoop microhardness)
• ISO 6507-1 (Vickers microhardness)
• ISO 9220 (SEM thickness measurement)
• ISO 26423 (crater-grinding thickness)
• ISO 20808 (ball-on-disc friction/wear)

Keywords: ISO 21874:2019, PVD multi-layer hard coatings, physical vapor deposition, composition structure properties, nano-indentation, microhardness, SEM, TEM, SIMS, EDS, GDOES, surface deficiency rate, thickness measurement.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 21874
First edition
2019-10
PVD multi-layer hard coatings —
Composition, structure and properties
Revêtements durs multicouches déposés par PVD — Composition,
structure et propriétés
Reference number
©
ISO 2019
© ISO 2019
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ii © ISO 2019 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Samples for composition, structure and properties evaluation . 1
5 Testing of composition, structure and properties . 1
5.1 Testing of chemical composition . 1
5.2 Testing of layer structure . 2
5.3 Testing of surface deficiency . 3
5.4 Testing of thickness . 4
5.5 Testing of properties . 4
5.5.1 Hardness . 4
5.5.2 Friction and wear . 6
Annex A (informative) Sample preparation and operation of transmission electron microscopy .7
Annex B (informative) Example of a surface deficiency rate calculation . 9
Foreword
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This document was prepared by Technical Committee ISO/TC 107, Metallic and other inorganic coatings,
SC 9, Physical vapor deposition coatings.
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iv © ISO 2019 – All rights reserved

Introduction
Multi-layer hard coatings by physical vapor deposition (PVD), which possess high coating-substrate
adhesion, high hardness and good wear resistance, are widely applied on tools and machine parts to
improve their service life. Based on the chemical compositions, the mainstream PVD multi-layer hard
coatings in the market involve transition metal nitrides and carbides, such as Ti/TiN, TiN/CrN, CrN/
AlCrN, TiC/TiCN and CrAlN/AlCrTiSiN. To date, there has been no standard to qualify the composition,
structure and properties of these multi-layer hard coatings, which has limited their further
development.
This document defines the measurement and evaluation of the composition, microstructure, surface
quality, thickness, hardness and tribological properties (such as friction and wear performance) of
multi-layer hard coatings. The methods are for the purpose of coating development. Where standards
for quality assurance in production exist, they are referred to in this document.
INTERNATIONAL STANDARD ISO 21874:2019(E)
PVD multi-layer hard coatings — Composition, structure
and properties
1 Scope
This document specifies the evaluation standard of the composition, structure and properties of
multi-layer hard coatings by common physical vapor deposition (PVD), indicating a vacuum deposition
method that produces a material source by evaporation, sputtering or related non-chemical ways.
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 4545-1, Metallic materials — Knoop hardness test — Part 1: Test method
ISO 6507-1, Metallic materials — Vickers hardness test — Part 1: Test method
ISO 9220, Metallic coatings — Measurement of coating thickness — Scanning electron microscope method
ISO 14577-1, Metallic materials — Instrumented indentation test for hardness and materials parameters
— Part 1: Test method
ISO 20808, Fine ceramics (advanced ceramics, advanced technical ceramics) — Determination of friction
and wear characteristics of monolithic ceramics by ball-on-disc method
ISO 26423, Fine ceramics (advanced ceramics, advanced technical ceramics) — Determination of coating
thickness by crater-grinding method
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
4 Samples for composition, structure and properties evaluation
Samples for the composition, structure and properties evaluation should be coated in the same batch
as the products requiring the composition, structure and properties evaluation. The samples should be
polished to a mirror finish (R < 0,05 μm) before being coated and cleaned using ultrasonic agitation,
pk
which immerses them in the correct solution to remove hydrocarbons and other surface contaminants.
5 Testing of composition, structure and properties
5.1 Testing of chemical composition
The chemical composition of PVD multi-layer hard coatings is decided by many factors, including
the composition of the evaporator source, the energy density of incident atoms/ions, the deposition
pressure and the bias voltage. Various elements in the evaporator source can segregate during
deposition, which results in different contents in the coatings. Testing methods that can be used to
characterize the chemical compositions of PVD multi-layer hard coatings are energy dispersive
spectrometer (EDS), electron probe micro analysis (EPMA), X-ray photoelectron spectrometer (XPS),
auger electron spectrometer (AES), secondary ion mass spectrometry (SIMS), X-ray fluorescence (XRF)
and glow discharge optical emission spectroscopy (GDOES). The details are shown in Table 1.
Table 1 — Testing methods of chemical compositions of PVD multi-layer hard coatings
Surface area Cross-sectional area
Testing
Maps and line scans
B, C, N and O B, C, N and O
method
Metal elements Metal elements
elements elements
Recommend-
Recommended Recommended Recommended
ed (monolayer
EDS (excluding Li and (excluding B and (excluding B and Recommended
thickness more
Be) C) C)
than 100 nm)
EPMA Recommended Recommended Recommended Recommended Recommended
Recommended Recommended Recommended
XPS Recommended Recommended
(only by etching) (only by etching) (destructive)
Preferably Preferably
AES Recommended Recommended Recommended
recommended recommended
Preferably Preferably Preferably Preferably Recommended
SIMS
recommended recommended recommended recommended (destructive)
XRF Recommended — — — —
Preferably rec- Preferably rec-
Preferably Preferably Recommended
GDOES ommended (only ommended (only
recommended recommended (destructive)
by etching) by etching)
5.2 Testing of layer structure
Different structures of PVD hard coatings observed by electron microscope, including columnar crystal,
equiaxed crystal and amorphous, lead to different grain or crystallite types, boundary energy and
texture, which influence their hardness, internal stress, toughness and adhesion. Therefore, structure
testing is essential for coating evaluation.
PVD multi-layer hard coatings can be defined in two classes. The first class comprises several different
layers consecutively, including the adhesive layer, transition layer, hard core layer and/or surface
adaptive layer for lubrication, hydrophobicity, electroconductivity, etc, as shown in Figure 1 a). The
other class comprises two kinds of layers, in which every two adjacent layers constitute a unit and the
thickness is called the "modulation period" (Λ = λ + λ ; λ and λ are the thickness of the A layer and
A B A B
B layer, respectively). It is called "nano-layered coating" when Λ is less than 100 nm or "super-lattice
coating", as shown in Figure 1 b).
Methods such as SIMS, scanning electron microscope (SEM) and transmission electron microscope
(TEM) are able to detect and confirm the layer structure of coatings. Detailed information about
analysing the layer structure by TEM is given in Annex A.
2 © ISO 2019 – All rights reserved

a)  Several d
...