GB/T 6462-2005/ISO 1463:2003
Metallic and Oxide Coatings – Measurement of Coating Thickness – Microscopical Method
Equivalent to ISO 1463:2003 (IDT)
Issued: 2005-06-23 | Implemented: 2005-12-01
Issued by: General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China
Standardization Administration of China
Foreword
This standard is identically adopted from ISO 1463:2003 “Metallic and oxide coatings – Measurement of coating thickness – Microscopical method” (English version).
This standard is an equivalent translation of ISO 1463:2003. For ease of use, the following editorial modifications have been made:
- a) Replace “this international standard” with “this standard”;
- b) Replace “that country” with “country”;
- c) Replace comma “,” as decimal separator with decimal point “.”;
- d) Delete the foreword of the international standard.
This standard replaces GB/T 6462-1986 “Microscopical method for measuring cross-sectional thickness of metallic and oxide coatings”. Main changes compared to GB/T 6462-1986:
- Standard title changed to “Metallic and oxide coatings – Measurement of coating thickness – Microscopical method”;
- Scope of application added (Chapter 1);
- Normative references added (Chapter 2);
- Definition of local thickness added (Chapter 3);
- Appendix B added.
1 Scope
This standard specifies a method for measuring the local thickness of metallic coatings, oxide film layers, and enamel or glass porcelain coatings using an optical microscope to examine cross-sections.
Warning: The use of this standard may involve hazardous materials, operations, and equipment. This standard does not address any health hazards or safety issues during use. Before using this standard, users are responsible for establishing appropriate health and safety regulations based on national or local requirements and taking corresponding measures.
2 Normative References
The following documents contain provisions that, through reference in this standard, constitute provisions of this standard. For dated references, subsequent amendments (excluding corrigenda) or revisions do not apply. However, parties are encouraged to investigate whether the latest versions of these documents can be used.
- GB/T 12334 – Metallic and other non-organic coatings – Notes on the measurement of thickness (idt ISO 2064)
3 Terms and Definitions
The terms and definitions from GB/T 12334 and the following apply to this standard:
3.1 Local thickness – The average value of a specified number of thickness measurements made within a reference area.
4 Principle
A test piece is cut from the component to be tested, mounted, and the cross-section is ground, polished, and etched using appropriate techniques. The thickness of the coating cross-section is measured using a calibrated scale.
Note: Experienced metallographers are familiar with these techniques. For inexperienced operators, guidance is provided in Chapter 5 and Appendix A.
5 Factors Affecting Measurement Uncertainty
5.1 Surface roughness – If the coating or substrate surface is rough, one or both interface lines in contact with the coating cross-section will be irregular, preventing precise measurement.
5.2 Cross-section tilt – If the cross-section is not perpendicular to the coating plane, the measured thickness will be greater than the true thickness. For example: a 1° deviation from perpendicularity produces a 1.5% error.
5.3 Coating deformation – Excessive temperature and pressure during mounting and cross-section preparation can cause harmful deformation in soft or low-melting-point coatings.
5.4 Coating edge chamfering – If the cross-section edge is chamfered, microscope measurement will not give the true thickness.
5.5 Additional plating – During cross-section preparation, an additional coating is often applied to protect the coating edge and avoid measurement errors.
5.6 Etching – Proper etching produces a fine, clear black line at the interface between two metals; excessive etching will blur the interface line or widen it, causing measurement errors.
5.7 Smearing – Improper polishing or additional plating of soft metal can cause one metal to smear over another, blurring the interface between coating and substrate.
5.8 Magnification – For any given coating thickness, measurement error generally increases with decreasing magnification. The microscope field of view should be 1.5 to 3 times the coating thickness.
5.9 Stage micrometer calibration – Errors in stage micrometer calibration will reflect in specimen measurements.
5.10 Micrometer eyepiece calibration – Linear micrometer eyepieces provide the most satisfactory thickness measurement method. The eyepiece should be calibrated by the operator performing the measurements.
5.11 Alignment – Backlash during micrometer eyepiece movement can also cause measurement errors.
5.12 Magnification uniformity – Non-uniform magnification across the field of view introduces errors.
5.13 Lens quality – Unclear images produce measurement uncertainty; high-quality lenses must be used.
5.14 Eyepiece orientation – Ensure the eyepiece reticle is perpendicular to the coating cross-section interface line during alignment.
5.15 Tube length – Changes in tube length cause magnification changes; avoid tube length changes between calibration and measurement.
6 Cross-Section Preparation
Preparation, mounting, grinding, polishing, and etching of specimens require:
- a) Cross-section perpendicular to the coating;
- b) Cross-section surface flat, with the entire image width in focus at the magnification used for measurement;
- c) Deformed material from cutting and cross-section preparation must be removed;
- d) The interface line on the coating cross-section must be clearly determinable by visual contrast or by a fine, easily distinguishable line.
7 Measurement
7.1 Proper attention should be paid to the various factors listed in Chapter 5 and Appendix A.
7.2 Calibrate the microscope and its measuring device using a verified or calibrated stage micrometer.
7.3 When measuring the width of the coating cross-section image, take at least five measurements along the length of the microsection.
8 Measurement Uncertainty
The microscope and its accessories, the methods of use and calibration, and the cross-section preparation methods should all be selected so that the measurement uncertainty is within the larger of 1 μm or 10% of the true thickness. This method can achieve an absolute measurement uncertainty of 0.8 μm; when the thickness is greater than 25 μm, a reasonable measurement uncertainty should be 5% or less.
Under good conditions, with careful specimen preparation and appropriate instruments, this method can achieve a measurement uncertainty of 0.4 μm.
9 Test Report
The test report should include:
- a) The number of this standard, i.e., GB/T 6462-2005;
- b) Characteristics of the test specimen;
- c) Description of measurement results:
- 1) Location of the cross-section on the test specimen;
- 2) Thickness at each measurement point, in micrometers (or millimeters if greater than 1 mm);
- 3) Local thickness, i.e., the arithmetic mean of thickness measurements.
- d) Any deviations from the designated process;
- e) Any abnormal features observed during testing;
- f) Date of testing.
Appendix A (Informative) – Guidelines on Cross-Section Preparation and Measurement
A.1 Introduction – Specimen preparation and coating thickness measurement largely depend on individual skill, and applicable techniques are diverse. Specifying a single technique is unreasonable, and including all applicable techniques is impractical. The techniques described in this appendix serve as guidelines for inexperienced metallographers.
A.2 Mounting – To prevent edge chamfering of the coating cross-section, support the outer surface of the coating so that no gap remains between the coating and the support. A metal with hardness similar to the coating is often plated on the specimen as an additional coating, with a thickness of at least 10 μm.
A.3 Grinding and Polishing – Maintaining the mounted cross-section perpendicular to the coating is critical. Plastic mounting with metal shims at the outer edge, periodic rotation of grinding direction (90°), and minimizing grinding time and pressure all help maintain cross-section perpendicularity.
A.4 Etching – Etching is usually appropriate to enhance contrast between metal layers, remove smearing traces, and reveal a clear fine line at the coating interface.
A.5 Measurement – Measuring instruments generally use linear micrometers or micrometer eyepieces, with the latter having lower accuracy.
Appendix B (Informative) – Measurement of Cross-Section Tilt and Serrated Structure Coatings
B.1 Cross-section tilt – If the specimen orientation deviates from the perpendicular plane (see Figure B.1), the measurement value will be higher.
Coating thickness d can be calculated by formula (B.1):
d = d’ × cos α
Where: d = coating thickness when α=0; α = deviation angle of cross-section from perpendicular to coating surface (in degrees); d’ = measured coating thickness when α≠0.
B.2 Measurement of serrated structure coatings – This method can be used to measure the local thickness of serrated structure coatings, such as boron nitride coatings produced by thermochemical processes.
B.3 Empirical values of measurement standard deviation using light microscopes – Under repeatable conditions, the standard deviation (σ) is 0.3 μm. Under comparative conditions, the standard deviation is 0.8 μm.
Appendix C (Informative) – Typical Etchants Used at Room Temperature
| No. | Etchant | Application |
|---|---|---|
| 1 | Nitric acid (ρ=1.42 g/mL): 5 mL; Ethanol (95% vol): 95 mL | For nickel and chromium coatings on steel; etches steel. Warning: This mixture is unstable and may explode, especially when heated. |
| 2 | Ferric chloride hexahydrate (10 g); Hydrochloric acid (ρ=1.16 g/mL): 2 mL; Ethanol (95% vol): 98 mL | For gold, lead, silver, nickel and copper coatings on steel, copper and copper alloys; etches steel, copper and copper alloys. |
| 3 | Nitric acid (ρ=1.42 g/mL): 50 mL; Glacial acetic acid (ρ=1.16 g/mL): 50 mL | For single layer thickness measurement of multi-layer nickel coatings on steel and copper. |
| 4 | Ammonium persulfate: 10 g; Ammonium hydroxide (ρ=0.88 g/mL): 2 mL; Distilled water: 93 mL | For tin and tin alloy coatings on copper and copper alloys; etches copper and copper alloys. |
| 5 | Nitric acid (ρ=1.42 g/mL): 5 mL; Hydrofluoric acid (ρ=1.14 g/mL): 2 mL; Distilled water: 93 mL | For nickel and copper coatings on aluminum and aluminum alloys; etches aluminum and aluminum alloys. |
| 6 | Chromic anhydride: 20 g; Sodium sulfate: 1.5 g; Distilled water: 100 mL | For nickel and copper coatings on zinc alloys; also suitable for zinc and cadmium coatings on steel. |
| 7 | Hydrofluoric acid (ρ=1.14 g/mL): 2 mL; Distilled water: 98 mL | For anodized aluminum alloys; etches aluminum and aluminum alloys. |
References
- BARGHOORN, H., Vergleichende Untersuchungen von Schichtdicke-Messverfahren, Metalloberflache, 1955, 7, pp. 8-11.
- Ray, G. P., Thickness testing of electroplated and related coatings, Electrochemical Publications Ltd., Asahi House, 10 Church Road, Port Erin, U. K., 1993, ISBN 0 901150 27 4.
Original Standard Document
GB/T 6462-2005/ISO 1463:2003 – Metallic and Oxide Coatings – Measurement of Coating Thickness – Microscopical Method (Chinese National Standard)