ASTM B487 — Coating Thickness by Microscopical Cross-Section Examination

TLDR

ASTM B487-85(2020) is the ASTM International standard test method for direct measurement of metal and oxide coating thickness by microscopical examination of a metallographic cross section. It is the most precise coating-thickness method for PVD coatings on titanium (TiN, TiAlN, DLC), anodized layers per AMS 2471, and passivation layers per AMS 2700.

Quick Answer

What does ASTM B487 cover?
ASTM B487 specifies the sectioning, mounting, polishing, and microscopic examination procedure for direct measurement of coating thickness on a metallographic cross-section. The method is destructive but gives a direct, calibrated measurement (versus XRF or eddy-current which are indirect) and is the referee method for disputes between producer and user.

Scope

ASTM B487 applies to metallic and oxide coatings on metallic substrates including PVD coatings (TiN, TiAlN, CrN, DLC), anodized layers, electroplated coatings, and chemical-conversion coatings. For titanium PVD, it is the standard thickness-verification method referenced by AMS 2444, AMS 2471, and VDI 3198.

Key test parameters:

• Section orientation: perpendicular to the coating surface (90° cross-section)
• Mounting: epoxy or phenolic resin mount; vacuum impregnation for porous coatings
• Polishing: standard metallographic sequence — SiC papers (120 → 600 grit) followed by diamond or alumina polishing (down to 0.05 µm)
• Etching: optional; may be required to reveal coating/substrate interface

Reporting

The report should include:

• Sample identification and section location
• Coating thickness measurements (individual values + mean ± standard deviation)
• Coating uniformity characterization
• Substrate material and surface preparation
• Magnification and measurement reference (e.g., calibrated reticle or image-analysis system)
• Photomicrographs at the measurement locations

For PVD coatings on titanium, a typical report might be:

TiN PVD on Grade 5 Ti-6Al-4V, AMS 2444
Cross-section B487 measurement @ 1000×
Measurements (µm): 2.8, 3.0, 2.9, 3.1, 2.9
Mean ± SD: 2.94 ± 0.11 µm
Acceptance: 1–5 µm per AMS 2444 — PASS

Common Pitfalls

• Edge rounding during polishing. Insufficient mount hardness or excessive polishing pressure causes the coating edge to round, making thickness measurement artificially low. Use a hard mount (filled epoxy) and minimal final-polish pressure.
• Coating pull-out. Soft or poorly-adhered coatings can pull out of the mount during polishing, leaving a gap. Vacuum impregnation prevents this.
• Inclined section. A non-perpendicular section makes the coating appear thicker than it actually is; verify 90° orientation before mounting.
• Coating damage during cutting. Slow-speed cutting with adequate coolant prevents heat-affected damage to thin (1–5 µm) PVD coatings.
• Single-point measurement. A single thickness measurement does not characterize uniformity; take ≥ 5 measurements across the section and report mean ± standard deviation.

Related Standards

• AMS 2444 — Coating, Physical Vapor Deposition of Titanium Nitride. Aerospace process specification for TiN PVD on titanium; B487 is the coating-thickness test method.
• AMS 2471 — Anodizing of Titanium and Titanium Alloys. Aerospace anodizing standard; B487 is used for anodized-layer thickness measurement.
• ASTM C633 — Adhesion or Cohesion Strength of Thermal Spray Coatings. Companion test method for adhesion; B487 is for thickness.
• VDI 3198 — Quality Assurance of PVD and CVD Coatings. European acceptance categories; B487 verifies thickness consistency.
• ISO 14577 — Instrumented Indentation Testing. Nanoindentation method for coating hardness; complements B487 for mechanical-property characterization.
• AMS 2700 — Passivation of Corrosion-Resistant Steels and Titanium Alloys. Pre-treatment standard for PVD; B487 verifies the passivation / oxide layer thickness.

For an overview of where PVD fits in the broader titanium surface-finish landscape, see the surface finishes hub and the dedicated PVD coating guide.

• Magnification: 500–1000× for PVD coatings (1–5 µm); 100–500× for thicker anodized layers
• Typical accuracy: ±0.1 µm at 1000× magnification

Test Procedure

1. Section. Cut the coated part perpendicular to the coating surface using a slow-speed saw with coolant to avoid coating damage. The cut should expose a clean cross-section through the coating and substrate.
2. Mount. Mount the section in epoxy or phenolic resin; use vacuum impregnation for porous or friable coatings to prevent edge-rounding during polishing.
3. Grind. Progress through SiC papers (120, 240, 400, 600 grit) with water lubrication; rinse between grits to avoid carry-over.
4. Polish. Diamond or alumina polishing (6 µm, 1 µm, 0.25 µm, optional 0.05 µm); final polish is critical for accurate coating-thickness measurement.
5. Etch (optional). Apply a chemical etch (e.g., Kroll’s reagent for titanium substrate) to reveal the coating/substrate interface if it is not visible from metallographic contrast alone.
6. Examine. Measure the coating thickness under calibrated optical microscopy at 500–1000×. Take 5+ measurements along the section to characterize thickness uniformity.