Case Study: Determination of Hardness and Modulus of Thin Films and Coatings by Nanoindentation:- INDICOAT Contract No.

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1 Case Study: Determination of Hardness and Modulus of Thin Films and Coatings by Nanoindentation:- INDICOAT Contract No. SMT4--CT Dr Nigel M. Jennett 10 th November 2011 This presentation was written by N.M. Jennett of the National Physical Laboratory. It is published with the permission of the Controller 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

2 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

3 INDICOAT background EC contract SMT4-CT INDICOAT Determination of Hardness and Modulus of Thin Films and Coatings by Nanoindentation. ( ) 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.

4 Traditional Hardness a quick and easy QA tool F d HV = const x F/d 2 Limited by optical resolution

5 Instrumented indentation Magnet Coil loading sample unloading sample C f Contact Area H IT = Stage LOAD FRAME Force Area Frame Compliance 1 1 E* A C C S 0.73

6 Elasticity is a far-field effect: Substrate effect ε t =σ (1/E coat + 1/E subst ) + ε p Indenter Indenter k COAT Indenter k SUBST

7 Typical material responses Aluminium Alumina Plastic work Plastic work Elastic work Data courtesy of VAMAS TWA22 Project 1 (1997)

8 VAMAS TWA22: Experimental information for scope of INDICOAT Typical load / unload curves - Berkovich indenter Alumina coating - effect of thickness 0.1 micron 0.3 micron 1.0 micron 3.0 micron 5.0 micron

9 INDICOAT results: The minimum requirements for obtaining valid data are: Calibration of: Force Displacement (Time etc.) Indenter Area Function Instrument Frame Compliance Avoid or correct for: Thermal drift Indentation creep Surface zero point error Traceability to National Standards (S.I.) (calibration methods developed) Validation through Certified Reference Materials (Need identified for CRM development)

10 Coating Property Measurement To measure Indentation Modulus of Coating Perform test indentations (two depths) Coating fractures? No Choose suitable indenter No Coating creeps? Yes Hold at F max until creep rate reduced Yes Change indenter? Increase radius? No Change indenter? Increase indenter radius or opening angle No No Perform indentations over the range zero to a/t c < 2 (hard or brittle) a/t c < 1.5 (ductile) Extrapolate Linear Fit to find coating E IT * at a/tc = 0 Yes Are forces below fracture limit Possible? Purely elastic response? Yes Quality Assurance Check Inspect indentations for cracking and pileup using Optics/SEM/AFM Yes Input or estimate Poisson ratio to calculate coating E IT INDICOAT protocol (ISO pt4) provides flowcharts / Decision trees for: System calibration and setup. Indenter selection Indentation cycle parameters. Data Acquisition. Drift corrections Analysis method. Result calculation. After Jennett and Bushby Proc MRS Symp 695 (2002) pp73-78

11 Instrumented indententation: TiN on Steel 600 (ISO (INDICOAT) test procedure) 500 Indentation modulus (E*) Intercept A = 456 GPa Intercept B = 449 GPa Intercept C = 464 GPa t = 0.95 µm t = 2.28 µm t = 2.66 µm Specimen A Specimen B Specimen C Radius of contact area / coating thickness

12 Nanoindentation of 250 nm Nb film (INDICOAT method) E IT * [GPa] 140 y = 39.86x ± 2* std error (U95) -5.00E E E E E E+00 contact radius/thickness ISO_valid data Linear (ISO_valid data)

13 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 : 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 normal comment and revision stages to become CEN/TS 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 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).

14 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.

15 Systematic Review - example INDICOAT ( ) 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 (~2003) [2003] ISO/TC 164/SC 3 start NWI based on CEN/TS 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 [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 2002 now proven necessary and may be adopted (a decade later).

16 Future Standardisation Certified Reference Materials now available (use can now be made normative). 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 retained and/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.

17 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

18 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.

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