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Scratch testing procedures for the testing of adhesive and cohesive strength of hard coatings, described in the European standard prEN 1071-3, require the measurement of �critical load� values associated with characteristic failure events occurring when a stylus is drawn across the coating with a normal load applied. The CRM BCR-692 has been produced and certified for verification and monitoring of the proper functioning of scratch test instruments. The reference samples are (30x30x5) mm steel coupons with a diamond-like carbon coating (DLC) applied by plasmaassisted chemical vapour deposition. Certification of critical load values was carried out by nine laboratories using three different types of scratch testing instruments and specially prepared Rockwell C diamond styli. A study of heterogeneity and stability was made and the sensitivity of critical load to stylus tip radius was also investigated.

Certified values were assigned for three critical loads Lc1, Lc2, Lc3 (corresponding to three particular failure events) with uncertainties arising from the evaluation of the material properties. In addition, machine �verification ranges� (wider than the certified ranges), to be used for verification of scratch test instruments were assigned, including additional components of uncertainty related to stylus variability and machine type. The verification ranges can be used to verify any scratch test instrument compliant with, and calibrated according to, prEN 1071-3.

Additional information

Authors: INGELBRECHT C, European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, Geel (BE);JENNETT N, European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, Geel (BE);JACOBS R, National Physical Laboratory, Teddington (GB);MENEVE J, National Physical Laboratory, Teddington (GB)
Bibliographic Reference: EUR 20986 EN (2004), 17 pp. Free of charge
Availability: Available from European Commission, JRC Knowledge Management Unit, Ispra (IT) Tel: +39 033278 9893 Fax: +39 033278 5409 E-mail: or Bruxelles (BE) Tel: +32 2 295 76 24 Fax: +32 2 299 63 2
ISBN: ISBN: 92-894-6870-X
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