ISO 14577 — Instrumented Indentation Testing for Hardness

TLDR

ISO 14577-1:2015 is the ISO standard for instrumented indentation testing (nanoindentation) of metallic materials. It is the standard method for measuring coating hardness and elastic modulus on PVD coatings (TiN, TiAlN, DLC) on titanium substrates, where the thin coating and small load require depth-sensing instrumentation rather than optical hardness measurement.

Quick Answer

What does ISO 14577 cover?
ISO 14577 specifies the instrumented-indentation test method for measuring hardness (HV) and elastic modulus (E, in GPa) at sub-millinewton loads. The method uses a diamond indenter (Berkovich or Vickers) and continuously records load and penetration depth during a controlled loading-unloading cycle. For titanium PVD coatings, the method gives hardness values such as TiN 1800–2500 HV 0.05 and TiAlN 2500–3200 HV 0.05.

Scope

ISO 14577 applies to metallic, ceramic, and coated materials where conventional optical hardness measurement is impractical — typically coatings thinner than ~10 µm, microstructural features smaller than the indentation, or phases requiring site-specific hardness. For titanium PVD, it is the workhorse method for coating hardness measurement referenced by AMS 2444 and VDI 3198.

Key test parameters:

• Indenter geometry: Berkovich (three-sided pyramid) or Vickers (four-sided pyramid)
• Maximum load: 1 mN to 30 N (macro range); 0.1–500 mN typical for PVD coatings
• Loading rate: controlled; typically 0.05–10 mN/s
• Hold at peak load: 5–10 s for creep correction
• Depth measurement: continuous, resolution ≈ 0.1 nm

Calculations

The instrumented-indentation hardness (HV or HIT) is calculated as:

HIT = F_max / A_p(h_c)

where:

• HIT = instrumented indentation hardness (MPa or HV)
• F_max = peak load (N)
• A_p = projected contact area at the contact depth h_c (mm²)

The contact depth h_c is determined from the peak load, peak displacement, and the slope of the unloading curve:

h_c = h_max − ε · F_max / S

where S is the contact stiffness (slope of the unloading curve at peak load) and ε is a geometric constant (0.75 for Berkovich, 1.0 for Vickers).

The elastic modulus is calculated from the contact stiffness using:

1/E_r = (1 − ν_i²)/E_i + (1 − ν_s²)/E_s

where E_r is the reduced modulus, E_i and ν_i are the indenter modulus and Poisson’s ratio, and E_s and ν_s are the sample modulus and Poisson’s ratio.

Typical Hardness Values for PVD Coatings on Titanium

The indentation depth must be less than 10 % of the coating thickness for the hardness measurement to reflect the coating alone (the “10 % rule”). For a 2 µm TiN coating, the maximum depth is 0.2 µm; this requires sub-mN loads.

Common Pitfalls

• Indentation too deep. If the indentation depth exceeds 10 % of the coating thickness, the hardness reflects the substrate, not the coating. Use lower loads or thinner coatings.
• Surface roughness. High surface roughness (Ra > 0.1 µm) produces noise in the depth measurement; the sample must be polished to a mirror finish.
• Creep correction. Titanium and titanium alloys exhibit significant indentation creep; without a hold at peak load, the measured hardness is too high. Apply the 5–10 s hold.
• Indenter wear. A worn Berkovich indenter produces inaccurate area function calibration; periodically verify the indenter geometry with a calibration sample.
• Thermal drift. Indentation depth changes of nanometers per second can produce significant error over a long test series; allow the system to thermalize and use drift correction.

Related Standards

• AMS 2444 — Coating, Physical Vapor Deposition of Titanium Nitride. Aerospace process specification for TiN PVD on titanium; ISO 14577 is the coating-hardness test method.
• VDI 3198 — Quality Assurance of PVD and CVD Coatings. European acceptance categories; ISO 14577 complements the VDI 3198 indentation test for hardness quantification.
• ASTM C633 — Adhesion or Cohesion Strength of Thermal Spray Coatings. Tensile-bond test; ISO 14577 gives hardness, C633 gives adhesion.
• ASTM B487 — Microscopical Cross-Section Thickness Measurement. Thickness verification; ISO 14577 verifies hardness consistency.

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.

• Hardness range: 0.1 HV to 30,000 HV (with appropriate load)

Test Procedure

1. Prepare. Mount the sample with a surface perpendicular to the indenter axis; polish to a smooth surface finish (typically Ra < 0.1 µm) for accurate depth measurement.
2. Calibrate. Run a calibration indentation on a reference material (typically fused silica, 9.2 GPa) before each sample series.
3. Load. Apply the indenter at controlled loading rate to the target maximum load.
4. Hold. Hold at peak load for 5–10 s to allow creep dissipation.
5. Unload. Unload at the same rate; record load-depth data continuously.
6. Analyze. Apply the Oliver-Pharr method (or equivalent) to extract hardness and elastic modulus from the unloading curve.