Metal Coating Hardness Test Method

Metal coatings mainly include electrodeposition layer, self-catalytic coating, spray coating (including explosion spray coating and plasma spray coating) and aluminum anodized coating layer.

Generally, the coating is relatively thin, and its hardness is often different from that of the substrate. The hardness of the coating is closely related to the performance of the material. Therefore, accurate determination of the hardness of the coating is closely related to the rational use of materials and the improvement of the coating process.

Testing method

The hardness test of the coating is usually carried out by microscopic and small load Vickers hardness test methods. In addition to the Vickers indenter, the Knoop indenter should sometimes be used.

The test force should be carefully selected because the coating is generally thin. If the test force is too large, the hardness value will be affected by the hardness of the substrate material; if the test force is too small, it is easy to introduce large errors, which will affect the accuracy of the test.

To obtain the most accurate hardness value of the coating, the maximum test force corresponding to the thickness of the coating should be used.

Speed ​​of applying test force

If the speed can be selected and adjusted, the speed of the indenter descent should be controlled at 15~70μm/S.

Test force dwell time

Under normal circumstances, the test force dwell time should be controlled within 10~15s. For particularly soft coatings such as lead and tin, the holding time can be appropriately extended, but the actual holding time must be stated in the test report.

Avoid vibration

Because the coating is thin and the test force is small, the influence of vibration is a serious source of error. In order to reduce the influence of vibration, the specimen can be mounted on a rigid support table.

Surface treatment of the specimen

The hardness of the coating can be measured on the surface or on the cross section, which should be determined according to the thickness of the coating and the surface condition. Whether it is carried out on the surface or on the cross section, the test surface should be chemically, electrolytically or mechanically polished.

In particular, mechanical polishing should minimize local heating or work hardening, otherwise the hardness value will change.

Radius of curvature

If the Vickers hardness must be measured on the surface of a specimen with a large curvature, the influence of the curvature should be corrected.

Brittle materials

It is recommended to use a Knoop indenter to test brittle materials. If the Vickers method must be used, the detection force should be reduced.

Motorized Loading Brinell Rockwell and Vickers Hardness Tester HBRVD-187.5

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