What Specimens Can Be Tested by Micro Vickers Hardness Tester? Can It Test Coatings?
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A micro Vickers hardness tester is the preferred instrument for surface hardness testing of thin layers, coatings and hardened layers. Many manufacturers and laboratories wonder: Can a micro Vickers hardness tester test coatings?
The short answer: Yes, micro Vickers hardness tester is highly suitable for coating hardness testing, but proper test load selection must be followed to avoid invalid measurement results.
1. Why Micro Vickers Hardness Tester Is Suitable for Coating Detection
Coatings (electroplating, PVD/CVD coating, thermal spray coating, anodizing layer, chemical conversion film) are usually very thin. Conventional Rockwell or standard Vickers hardness testers use large test loads; the indentation will penetrate the coating and sink into the substrate metal, resulting in measured hardness values being a mixture of coating and substrate, rather than the true hardness of the coating itself.
Micro Vickers hardness tester adopts ultra-low test force (HV0.01 ~ HV0.5), produces tiny indentation. When operated correctly, the indentation is limited inside the coating layer, which can reflect the real hardness of surface coatings.
2. General Rule for Load Selection When Testing Coatings
Follow the industry universal rule: The depth of indentation shall not exceed 1/10 of the coating thickness.
If coating thickness ≥ 20μm：HV0.1 ~ HV0.3 is commonly used
If coating thickness 5～20μm：HV0.025 ~ HV0.05 is recommended
If coating thickness ＜5μm：Select HV0.01; fully automatic vision micro Vickers hardness tester is preferred
Important warning: If the test load is too large, the indentation penetrates the coating, the test data will be seriously distorted and cannot be used for acceptance evaluation.
3. Common Types of Coatings Suitable for Micro Vickers Test
Electroplating coatings: chrome plating, nickel plating, zinc plating, copper plating
Vacuum coating: PVD TiN, TiCN, DLC, CVD coating
Thermal spray coatings: sprayed ceramic coating, sprayed metal alloy coating
Surface treatment layers: anodized film, nitrided layer, carburized layer, QPQ layer
Organic hard coating, chemical plating nickel-phosphorus layer
4. Key Preconditions for Valid Coating Hardness Test
Sample preparation: The test surface must be flat, polished, free of scratches, oxide skin and pollution; the cross-section method is often adopted for ultra-thin coatings.
Vertical loading: Ensure the indenter is perpendicular to the coating surface, tilt will cause irregular indentation.
Distance standard: The indentation shall keep enough distance from the edge of sample and adjacent indentations, in accordance with ISO 6507 and GB/T 4340.1.
Avoid excessive load: Do not use HV1.0 or higher load for thin coatings.
5. What Equipment to Choose for Coating Hardness Testing
Manual micro Vickers hardness tester: Suitable for thick coatings above 20μm, low daily testing volume
Semi-automatic / Fully automatic vision micro Vickers hardness tester: Recommended for thin coatings below 20μm. With CCD automatic indentation recognition, it can accurately measure tiny indentations and effectively reduce human error.
FAQ
Q: Can HR-150A Rockwell hardness tester test coating hardness? A: Not recommended. The indenter penetration depth of Rockwell tester is large, almost all thin coatings cannot be measured independently.
Q: Can ordinary Vickers hardness tester (HV1~HV5) test coating? A: Only applicable to extra thick coatings. Most functional coatings are too thin; large loads will penetrate the coating and affect results.
Q: Can coating hardness be measured directly on the workpiece surface? A: Yes, if the coating thickness meets the load matching requirement. For ultra-thin coatings, metallographic cross-section sampling is more reliable.
Foosean micro Vickers hardness tester supports multiple micro loads from HV0.01 to HV0.5, equipped with high-magnification objective lens and optional automatic vision measurement system. It complies with ISO 6507 and GB/T 4340.1 standards, ideal for hardness inspection of various electroplating, vacuum PVD and thermal spray coatings.
