Case Study: Determination of Hardness and Modulus of Thin Films and Coatings by Nanoindentation :-“INDICOAT ”Contract No. SMT4- -CT98-2249

Dr Nigel M. Jennett10th November 2011

This presentation was written by N.M. Jennett of the National Physical Laboratory. It is published with the permission of the Controll er of HMSO and the Queen’s Printer for Scotland.

Crown Copyright covers this work - any reproduction requires written consent.This may be obtained from the author: nigel.jennett @npl.co.uk

Outline

� INDICOAT - a brief background� The problem being solved� The solutions found

� Standardisation activity resulting from the project� Systematic review of standards - general� Systematic review of standards - specific example� Future plans for further standardisation

INDICOAT background

� A 1992 report identified Surface Engineering and coatings as a growing market worth many billion Euro, that desperately needed measurement methods for quality control and product development.

� EC Dedicated call for pre-normative research to support mandates in both CEN/TC262/SC1/WG1 and CEN/TC184/WG5 for the drafting of ENV for the measurement of thin film and coating mechanical properties by instrumented indentation.

� The overall objective of INDICOAT was to provide the research basis for the drafting of a robust standard (including measurement and analysis protocols) to fulfil these mandates.

EC contract SMT4-CT98-2249 ‘INDICOAT’“Determination of Hardness and Modulus of Thin Films and Coatings by Nanoindentation.” (1998-2001)

Traditional Hardness – a quick and easy QA tool

F

d

HV = const x F/d2

Limited by optical resolution

0.73

loading unloading

samplesample

loading unloading

samplesample

loadingloading unloading

samplesample

loading unloading

samplesample

loading unloading

Instrumented indentation

StageLOAD FRAME

Coil

Magnet

0.73

Area

ForceH IT =

Cf

Frame

Compliance

SC CAE

11* ×∝

Contact

Area

Elasticity is a “far-field” effect:“Substrate effect”

Indenter

εt=σ (1/Ecoat + 1/Esubst) + εp

Indenter

Indenter

kCOAT

kSUBST

Aluminium

Plasticwork

Alumina

Elasticwork

Plasticwork

Typical material responses

Data courtesy of VAMAS TWA22 Project 1 (1997)

VAMAS TWA22: Experimental information for scope of INDICOAT

� Typical load / unload curves - Berkovich indenterAlumina coating - effect of thickness0.1 micron 0.3 micron 1.0 micron

3.0 micron 5.0 micron

INDICOAT results:

The minimum requirements for obtaining valid data are:� Calibration of:

ForceDisplacement(Time etc.)Indenter Area FunctionInstrument Frame Compliance

� Avoid or correct for:Thermal driftIndentation creepSurface zero point error

� Traceability to National Standards (S.I.)(calibration methods developed)

� Validation through Certified Reference Materials(Need identified for CRM development)

Coating Property Measurement

After Jennett and Bushby

Proc MRS Symp 695 (2002) pp73-78

To measure Indentation Modulus of

Coating

Choose suitable indenter

Perform test indentations

(two depths)

Perform indentations over the range zero to

a/t c < 2 (hard or brittle) a/t c < 1.5 (ductile)

Purely elastic

response? No

No

Extrapolate Linear Fit

to find coating E IT * at a/tc = 0

Yes

Yes

Coating creeps?

Yes

No

Hold at F max until creep rate reduced

Quality Assurance Check Inspect indentations for cracking and pileup

using Optics/SEM/AFM

Input or estimate Poisson ratio to

calculate coating E IT

No

Coating fractures?

No Yes

Yes

Increase indenter radius

or opening angle Are

forces below fracture limit

Possible?

Change indenter? Increase radius?

Change indenter? INDICOAT protocol (ISO 14577 pt4) provides flowcharts / Decision trees for:• System calibration and setup.• Indenter selection• Indentation cycle parameters.• Data Acquisition.• Drift corrections• Analysis method.• Result calculation.

Instrumented indententation: TiN on Steel

Intercept A = 456 GPa

Intercept B = 449 GPa

Intercept C = 464 GPa

0

100

200

300

400

500

600

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

Radius of contact area / coating thickness

Inde

ntat

ion

mod

ulus

(E

*)

Specimen ASpecimen BSpecimen C

(ISO 14577-4 (INDICOAT) test procedure)

t = 0.95 µmt = 2.28 µmt = 2.66 µm

Nanoindentation of 250 nm Nb film(INDICOAT method)

y = 39.86x + 100.85

80

100

120

140

160

180

200

-5.00E-01 0.00E+00 5.00E-01 1.00E+00 1.50E+00 2.00E+00

contact radius/thickness

EIT

* [G

Pa]

ISO_valid dataLinear (ISO_valid data)

± 2* std error (U95)

Standardisation of outputs

� Project calibration methods and other know-how injected into:ISO/TC 164/SC 3 for drafting of standard for the basic indentation

method. (ISO 14577 : 2002 parts 1 - 3) � Draft ENV delivered and submitted as WI-152 to CEN TC184 WG5

(notified to CEN TC 262 SC1). This progressed through the normalcomment and revision stages to become CEN/TS 1071-7

� Draft ENV (WI152) adopted as a NWI by ISO/TC 164/SC 3 in July 2003 and following the ISO process (WD - CD - DIS - FDIS) “parallel voted”to become EN ISO 14577 part 4 : 2007

Note:Dissemination to CEN and ISO was achieved by investing significant effort

in direct presentation of INDICOAT output to the relevant standards committees and willingness to follow through by being co-opted ( > 2 meetings per year). (Initially interested committees: CEN TC 184 WG5, CEN TC 262 SC1, ISO/TC 164/SC 3, ISO/TC107).

Systematic Review - Why?

Periodic reviews allow a standard to be fixed for a period yet accumulate changes that can be incorporated at regular review points (every 3y to 5y).� Standardisation involves an evolutionary development of

consensus. � Things change + better methods develop.� Users’ comments/misunderstandings are collected and filtered

back.New developments can be standardised as separate additional parts (e.g.

ISO14577 part 4). Improved methods can then be incorporated during systematic review.

Vienna convention requires withdrawal of equivalent EN standards upon publication of EN ISO standards. When there is a disconnect in the parallel voting system (I.e. no formal CEN - ISO liaison in place) this can be done by systematic review.

Systematic Review - example

INDICOAT (1998-2001)This is developing a test method for coatings with no standard test method existing for bulk materials. This is developed by default (using previous EC project outputs).

[1998] ISO/TC 164/SC 3 start NWI on instrumented indentation based on a German DIN standard for “Universal Hardness.” INDICOAT coordinator co-opted to develop comprehensive standard. Becomes ISO14577:2002 parts 1-Method; 2-Calibration; 3-Reference blocks.

[2001] CEN TC 184 WG5 WI 151 …becomes CEN/TS 1071-7 (~2003)

[2003] ISO/TC 164/SC 3 start NWI based on CEN/TS 1071-7 becomes ISO14577 part 4 :2007

[~2005] ISO14577:2002 first systematic review decides to wait for part 4.

[2007] CEN TC 184 WG5 withdrawal of CEN/TS 1071-7

[2008] ISO/TC 164/SC 3 In the next review decided to revise ISO14577 parts 1-3 in line with part 4. Still in process! Improved contact mechanics equations proposed by INDICOAT but not adopted in 2002now proven necessary and may be adopted (a decade later).

Future Standardisation

� Certified Reference Materials now available (use can now be madenormative).

� VAMAS TWA22 “Mechanical Properties of thin films and coatings”ISO14577 part 4 intercomparisons (proj 4: superhard coatings; Proj. 5: soft metal coatings) - will feed results into next systematic review.

� Methods to obtaining stress-strain curves by indentation currently ISO/TR29381 is in systematic review (could be retainedand/or an NWI initiated for ISO standardisation)

� Framework Prog. Article 169 European Metrology Research:� Measurement of mechanical properties of viscous materials

NWI for ISO14577 Part 5 planned. (Liaison with ISO/TC 61/SC2)� Creep and indentation at elevated temperatures

possible NWI for elevated/high temperature indentation section as part 6 or incorporated in Parts 1 - 4 (@next review?)

� Nanoimpact testing looking for incorporation in existing NWI for LEEB (rebound) hardness testing or ISO14577.

Comments

� Start with the end (standardisation) in mind� Include deliverables that are ISO/CEN friendly� Be prepared to get involved (early)

� build consensus � provide technical support to the process

� Have a long term strategy. � Current projects have to fund standardisation of

previous projects’ output.� Strategic alliances with standards committee

members� Systematic review - is both threat and opportunity

Acknowledgements

� The voluntary input of members of VAMAS TWA22 is gratefully acknowledged

� Work presented here was carried out with funding by the European Union

� Funding was also received from the National Physical Laboratory through the UK Government National Measurement Office.

� Thank you for your attention.