Vickers Hardness Testing: Principle, Applications, and Limitations

Vickers Hardness Testing: Principle, Applications, and Limitations

The Vickers hardness test presses a four-sided diamond pyramid into a material with a defined force, leaving an indentation on its surface. The unit is HV.

• Diamond indenter design: a four-sided pyramid with an included angle of 136° between opposite faces.
• Applied forces: 30 N, 50 N, 100 N, 150 N, 300 N, and others, depending on the application.

Indenter design:

• A square-based diamond pyramid with a 136° angle ensures geometric similarity at every load.
• This angle minimizes elastic deformation and standardizes results across materials of different hardness.

Calculation formula:

Vickers hardness is F/S: force F divided by the indentation surface area S. The area S is calculated from the mean lengths of the two indentation diagonals, d1 and d2.

• HV: Vickers hardness value (kgf/mm² or N/mm²).
• F: Applied force (kgf or N).
• d: Mean length of the two indentation diagonals (mm).
• Results can be compared across different loads because the method is independent of scale.

Vickers hardness is calculated as F/S: divide the test force F by the indentation area S. The area is based on the mean diagonal length d of the indentation made by the diamond pyramid.

Load ranges:

• Microhardness (1–1,000 gf): For thin coatings or small parts.
• Macrohardness (1–120 kgf): For bulk materials.

Test Procedure

Sample preparation:

• Polish the sample surface (Ra ≤ 0.5 µm) to ensure accuracy.
• Rough surfaces or coatings can distort the results.

Making the indentation:

• Apply the force for 10–15 seconds (per ISO 6507).
• The diamond indenter creates permanent plastic deformation.

Optical analysis:

• Measure the diagonals (d₁ and d₂) with a microscope or an automated system.
• Modern systems achieve ±0.5% accuracy using high-resolution images.

Advantages

1. Versatility:
   • Tests metals, ceramics, polymers, and composites (8–3,000 HV).
   • No need to change the indenter for different materials.
   • Measures the hardness of plated layers.
   • Measures very small parts that other methods cannot handle.
2. High accuracy:
   • Repeatable results, even with brittle materials such as glass.
   • Less sensitive to surface roughness than the Rockwell method.
3. Microhardness testing:
   • Evaluates thin coatings (such as PVD) or heat-affected zones in welds.
4. Minimal damage to the sample:
   • The small indentation allows the sample to be reused.
   • Provides accurate, reliable measurements across a wide range.

Limitations

1. Time-consuming:
   • One test cycle (preparation and measurement) takes 30–60 seconds.
2. High cost:
   • Diamond indenters and optical systems are expensive.
   • Manual testing requires skilled technicians.
   • Vickers hardness testers are expensive.
   • Additional sample-cutting and polishing equipment may be needed.
3. Surface sensitivity:
   • For multilayer materials, control thickness to avoid substrate effects.

Applications by Industry

Comparison with Other Methods

Advances and Trends

1. Automation:
   • AI systems (for example, the 3SMRTM algorithm) automatically measure diagonals, reduce errors, and reach 1.57-pixel accuracy.
   • Portable testers with touchscreens support on-site inspection.
2. Market:
   • The market is expected to grow 6.6% annually from 2024 to 2031, mainly in Asia-Pacific (48% market share).
   • Automotive and electronics account for 40% of sales.
3. Sustainability:
   • Eco-friendly materials, such as biodegradable polymers, require precise hardness testing.

FeaturedVickers hardness testersmodels

AFFRI hardness testers – Italy

AFFRI has led hardness tester research and manufacturing for more than 65 years.

The company’s highest-end Vickers and Knoop tester offers flexible features and test loads to meet user requirements.

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